Post on 08-Apr-2015
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A thesis Submitted for the degree
Doctor of Philosophy
by
Anthony Blazevich, BSc (Hons)
School of Exercise Science and Sport Management
Southern Cross University, Lismore, Australia
2000.
EFFECT OF MOVEMENT PATTERN AND
VELOCITY OF STRENGTH TRAINING
EXERCISES ON TRAINING ADAPTATIONS
DURING CONCURRENT RESISTANCE AND
SPRINT/JUMP TRAINING
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DECLARATION
The work presented in this thesis is the original work of the author except where
acknowledged in the text. I hereby declare that I have not submitted this material
either in whole or in part for a degree at this or any other institution.
____________________ _________________
Anthony Blazevich.
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ACKNOWLEDGMENTS
I’d first of all like to acknowledge my supervisors Dr. Robert Newton and Assoc.
Prof. Roger Bronks who gave me the freedom to pursue my research interests
while keeping a firm watch over me. Their belief in my ability has given me the
confidence to complete my this thesis.
Assoc. Prof. Greg Wilson who brought me to Southern Cross University and
ensured that I remembered exactly what I was wanted to research and was not
only my first PhD supervisor, but also helped me through many tough times.
My fellow postgraduates, Nick Gill, Anthony Giorgi, Tony Shield, Adam
Bryant, Nathan Deans and Phil Smith who all at some point or another helped
me with my research and put up with my whingeing.
The School of Exercise Science and Sport Management for providing me with
the opportunity to develop my knowledge in the Sport Science field, and for
providing the funding for my research. Also, the American Society of
Biomechanics whose Student Grant-in-Aid progam jointly funded my research.
Mr. Terry Woods for having faith in my teaching and researching ability and
allowing me to teach while completing the final stages of my Thesis.
My parents, Ron and Yvonne, and my brother Michael for letting me know that
it wasn’t just OK, but obligatory for me to fulfil my ambition to become the best
sports scientist I could be even though I’d have to live as a student for many
years.
To all of the subjects, and my friends in Lismore, who so graciously gave their
time and effort to help me. Many of my subjects offered their time and support for
little personal reward, I will never forget that.
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To my genuine support staff Carol Hayllar, Sharee Mulcahy, Carol Hartmann,
Tiffeny Byrnes, Rob Baglin and Mark Fisher. They not only provided support
essential for me to complete my work, but to kept me sane when I was bordering
on insanity.
A final mention must also be made to two people who have been there for me
through both the tough times and the good, who provided inspiration and support
when I needed it, who counselled me when I was down, and were unselfishly
happy for me when I achieved. First, Nick Gill who was there from the beginning
to not only help me be the scientist I am today, but the person I am as well. No
one has accompanied me through more of a metamorphosis than him. And
second, Jen Goward for her care and constant belief in my ability, and also for
putting up with my constant mood swings.
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PUBLICATIONS/PRESENTATIONS FROM THESIS
Blazevich, A.J. & Gill, N. (2001). Reliability and validity of two isometric squattests. Journal of Strength and Conditioning Research. In Press.
Conference Presentations
Blazevich, A.J.*, Newton, R.U. & Bronks, R. (2000). Podium Presentation -Movement specificity of muscle architectural changes after concurrent sprint/jumpand resistance training. The 2nd International Conference on Weightlifting andStrength Training, Ipoh Malaysia, 2000.
Blazevich, A.J.*, Bronks, R. & Newton, R.J. (2000). Movement specificity ofmuscle architectural changes after concurrent sprint/jump and resistancetraining.2000 Pre-Olympic Congress, Brisbane Australia, 2000.
Blazevich, A.J.*, Newton, R.U., Sharman, M., Bronks, R. & Gill, N. (2000).Specificity of Strength training exercises to the vertical jump and 20 m sprint tests.Australian and New Zealand Society of Biomechanics Conference, Gold CoastAustralia, 2000.
Blazevich, A.J.*, Newton, R.U., Bronks, R. & Gill, N. (1999). Influence ofmovement pattern of resistance training on athletic performance during concurrentresistance and task training. IOC World Congress in Sports Science, SydneyAustralia, 1999.
Blazevich, A.J.*, Newton, R.U., Sharman, M., Bronks, R. & Gill, N. (1999).Specificity of strength training exercises to the sprint run and vertical jump tests.IOC World Congress in Sports Science, Sydney Australia, 1999.
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TABLE OF CONTENTS
DDEECCLLAARRAATTIIOONN ......................................................................................................................................IIII
AACCKKNNOOWWLLEEDDGGMMEENNTTSS ..........................................................................................................................IIIIII
PPUUBBLLIICCAATTIIOONNSS//PPRREESSEENNTTAATTIIOONNSS FFRROOMM TTHHEESSIISS ..................................................................................... VV
CONFERENCE PRESENTATIONS........................................................................................................ V
TTAABBLLEE OOFF CCOONNTTEENNTTSS............................................................................................................................. II
LLIISSTT OOFF FFIIGGUURREESS .................................................................................................................................VVII
LLIISSTT OOFF TTAABBLLEESS...................................................................................................................................IIXX
LLIISSTT OOFF AABBBBRREEVVIIAATTIIOONNSS .....................................................................................................................XXII
ABSTRACTS....................................................................................................................................... XIII
STUDY ONE: A COMPARISON OF MOVEMENT PATTERNS OF THE VERTICAL JUMP, BROAD JUMP AND
ACCELERATION PHASE OF THE SPRINT RUN TO THE SQUAT LIFT AND FORWARD HACK SQUAT
EXERCISES. ....................................................................................................................................XIV
STUDY TWO: RELIABILITY AND VALIDITY OF TWO ISOMETRIC SQUAT AND FORWARD HACK SQUAT
TESTS .............................................................................................................................................XVI
STUDY THREE: RELIABILITY OF UNILATERAL AND BILATERAL FORWARD HACK SQUAT TESTS XVII
STUDY FOUR: PERFORMANCE RELATIONSHIPS BETWEEN VERTICAL JUMP, SPRINT RUNNING AND
STRENGTH TRAINING EXERCISES: IMPLICATIONS FOR MOVEMENT SPECIFICITY ........................ XVIII
STUDY FIVE: NEUROMUSCULAR AND PERFORMANCE ADAPTATIONS TO SHORT-TERM CONCURRENT
RESISTANCE AND SPRINT/JUMP TRAINING. .....................................................................................XIX
11..11 IINNTTRROODDUUCCTTIIOONN .............................................................................................................................. 22
11..22 PPUURRPPOOSSEE ........................................................................................................................................ 55
11..33 SSIIGGNNIIFFIICCAANNCCEE OOFF SSTTUUDDYY................................................................................................................ 66
11..44 OOVVEERRVVIIEEWW OOFF SSTTUUDDIIEESS .................................................................................................................. 77
1.4.1 STUDY ONE ............................................................................................................................ 7
1.4.2 STUDY TWO............................................................................................................................ 7
1.4.3 STUDY THREE......................................................................................................................... 8
1.4.4 STUDY FOUR........................................................................................................................... 8
1.4.5 STUDY FIVE ............................................................................................................................ 8
11..55 LLIIMMIITTAATTIIOONNSS ............................................................................................................................... 1100
11..66 DDEELLIIMMIITTAATTIIOONNSS ............................................................................................................................ 1111
CHAPTER 2: LITERATURE REVIEW.............................................................................................. 12
2.1 INTRODUCTION ....................................................................................................................... 13
2.2 EFFECT OF RESISTANCE TRAINING MOVEMENT PATTERN ON TASK PERFORMANCE ............. 14
2.2.1 Body position ................................................................................................................................... 14
2.2.2 Joint angles and muscle lengths ......................................................................................................... 16
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2.2.3 Unilateral versus bilateral specificity ................................................................................................. 23
2.2.4 Type of contraction ........................................................................................................................... 25
2.2.5 Type of pre-contraction ..................................................................................................................... 26
2.2.6 Summary .......................................................................................................................................... 27
2.3 EFFECT OF RESISTANCE TRAINING MOVEMENT VELOCITY ON TASK PERFORMANCE ........... 28
2.3.1 Isokinetic, velocity-specific training studies ....................................................................................... 28
2.3.2 Isokinetic training effects on task performance................................................................................... 30
2.3.3 Free-weight, isotonic training studies................................................................................................. 30
2.3.4 Mechanisms contributing to velocity-specific strength changes........................................................... 32
2.3.5 Summary .......................................................................................................................................... 47
2.4 BENEFITS OF RESISTANCE TRAINING TO HIGH-SPEED TASK PERFORMANCE ......................... 48
2.4.1 Strength and mass of muscle and connective tissue ............................................................................ 48
2.4.2 Consequences of Resistance Training for High-speed Task Performance ............................................ 50
2.4.3 Summary .......................................................................................................................................... 51
2.5 IMPLICATIONS OF THE LITERATURE REVIEW ......................................................................... 52
CCHHAAPPTTEERR 33:: SSTTUUDDYY OONNEE............................................................................................................. 5544
AA CCOOMMPPAARRIISSOONN OOFF MMOOVVEEMMEENNTT PPAATTTTEERRNNSS OOFF TTHHEE VVEERRTTIICCAALL JJUUMMPP,, BBRROOAADD JJUUMMPP AANNDD
AACCCCEELLEERRAATTIIOONN PPHHAASSEE OOFF TTHHEE SSPPRRIINNTT RRUUNN TTOO TTHHEE SSQQUUAATT LLIIFFTT AANNDD FFOORRWWAARRDD HHAACCKK SSQQUUAATT
EEXXEERRCCIISSEESS........................................................................................................................................... 5555
3.1 INTRODUCTION ................................................................................................................. 55
3.2 METHODS............................................................................................................................ 57
3.2.1 Subjects............................................................................................................................................ 57
3.2.2 Overview.......................................................................................................................................... 58
3.2.3 Videography ..................................................................................................................................... 58
3.2.4 Description of movement tasks.......................................................................................................... 60
3.2.5 Analysis of video data....................................................................................................................... 65
3.2.6 Statistical Analysis............................................................................................................................ 69
3.3 RESULTS............................................................................................................................... 70
3.3.1 General Movement Descriptions........................................................................................................ 70
3.3.2 Comparisons of Task Movement Patterns .......................................................................................... 74
3.4 DISCUSSION ........................................................................................................................ 83
CHAPTER 4: STUDY TWO.................................................................................................................. 87
RREELLIIAABBIILLIITTYY AANNDD VVAALLIIDDIITTYY OOFF IISSOOMMEETTRRIICC SSQQUUAATT AANNDD FFOORRWWAARRDD HHAACCKK SSQQUUAATT TTEESSTTSS .................. 8888
4.1 INTRODUCTION ................................................................................................................. 88
4.2 METHODS............................................................................................................................ 90
4.2.1 Subjects............................................................................................................................................ 90
4.2.2 Testing ............................................................................................................................................. 90
4.2.3 Data analysis..................................................................................................................................... 93
4.3 RESULTS .............................................................................................................................. 93
4.3.1 Reliability of ISQ and IFHS .............................................................................................................. 93
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4.3.2 Validity of isometric measures .......................................................................................................... 94
4.4 DISCUSSION ........................................................................................................................ 96
4.4.1 Reliability and validity ...................................................................................................................... 96
4.4.2 Movement specificity ........................................................................................................................ 98
4.4.3 Practical applications ........................................................................................................................ 98
4.4.4 Future research ................................................................................................................................. 99
4.4.5 Conclusion...................................................................................................................................... 100
CHAPTER 5: STUDY THREE............................................................................................................ 101
RELIABILITY OF UNILATERAL AND BILATERAL FORWARD HACK SQUAT TESTS......................... 102
5.1 INTRODUCTION ............................................................................................................... 102
5.2 METHODS.......................................................................................................................... 103
5.2.1 Subjects.......................................................................................................................................... 103
5.2.2 Protocol .......................................................................................................................................... 104
5.2.3 Determination of testing loads ......................................................................................................... 104
5.2.4 Test contractions............................................................................................................................. 105
5.2.5 Data analysis................................................................................................................................... 105
5.3 RESULTS ............................................................................................................................ 106
5.4 DISCUSSION ...................................................................................................................... 107
CHAPTER 6: STUDY FOUR ......................................................................................................... 109
PPEERRFFOORRMMAANNCCEE RREELLAATTIIOONNSSHHIIPPSS BBEETTWWEEEENN VVEERRTTIICCAALL JJUUMMPP,, SSRRIINNTT RRUUNNNNIINNGG AANNDD SSTTRREENNGGTTHH
TTRRAAIINNIINNGG EEXXEERRCCIISSEESS:: IIMMPPLLIICCAATTIIOONNSS FFOORR MMOOVVEEMMEENNTT SSPPEECCIIFFIICCIITTYY ............................................... 111100
6.1 INTRODUCTION ............................................................................................................... 110
6.2 METHODS.......................................................................................................................... 112
6.2.1 Subjects.......................................................................................................................................... 112
6.2.2 Procedure ....................................................................................................................................... 112
6.2.3 Data Analysis ................................................................................................................................. 118
6.3 RESULTS ............................................................................................................................ 119
6.4 DISCUSSION ...................................................................................................................... 122
CHAPTER 7 – STUDY FIVE .............................................................................................................. 126
NNEEUURROOMMUUSSCCUULLAARR AANNDD PPEERRFFOORRMMAANNCCEE AADDAAPPTTAATTIIOONNSS TTOO SSHHOORRTT--TTEERRMM CCOONNCCUURRRREENNTT RREESSIISSTTAANNCCEE
AANNDD SSPPRRIINNTT//JJUUMMPP TTRRAAIINNIINNGG ............................................................................................................ 112277
7.1 INTRODUCTION ............................................................................................................... 127
7.1.1 Muscle Architecture........................................................................................................................ 128
7.1.2 Longitudinal Research..................................................................................................................... 129
7.2 METHODS.......................................................................................................................... 130
7.2.1 Subjects.......................................................................................................................................... 130
7.2.2 Protocol .......................................................................................................................................... 131
7.2.3 Testing ........................................................................................................................................... 133
7.2.4 Training.......................................................................................................................................... 142
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7.2.5 Data analysis................................................................................................................................... 146
7.3 RESULTS ............................................................................................................................ 148
7.3.1 Performance Changes with Training ................................................................................................ 148
7.3.2 Isokinetic Knee Extension Torque ................................................................................................... 149
7.3.3 Muscle Size and Architecture .......................................................................................................... 150
7.3.4 Electromyographic Changes............................................................................................................ 157
7.5 DISCUSSION ...................................................................................................................... 162
7.5.1 Performance Changes with Training ................................................................................................ 162
7.5.2 Body Position-specific Strength Changes......................................................................................... 164
7.5.3 Joint Angle-specific Strength Changes............................................................................................. 164
7.5.3 Laterality-specific Strength Changes................................................................................................ 166
7.5.4 Velocity-specific Isokinetic Torque Changes ................................................................................... 167
7.5.5 Changes in Muscle Architecture ...................................................................................................... 168
7.5.6 Muscle Recruitment Pattern Changes with Training ......................................................................... 173
7.5.7 Practical Implications...................................................................................................................... 176
CHAPTER 8: THEORY ON EARLY ADAPTATIONS TO RESISTANCE TRAINING ................ 179
8.1 DOCUMENTATION OF THEORY .............................................................................................. 180
8.1.1 Are strength changes related to muscle activation? ........................................................................... 180
8.1.2 How does muscle strength increase with resistance training? ............................................................ 182
8.1.3 How would muscle architecture affect strength?............................................................................... 183
8.1.4 Is there a neural explanation for angle-specific strength changes? ..................................................... 184
8.1.6 How does muscle strength increase in a velocity-specific manner?.................................................... 189
8.1.7 What about conflicts in architecture and fibre type?.......................................................................... 189
8.1.8 Conclusion...................................................................................................................................... 191
8.2 ‘PERIPHERAL ADAPTATIONS’ EXAMPLE OF STRENGTH CHANGES AFTER RESISTANCE EXERCISE.
..................................................................................................................................................... 191
8.2.1 What adaptations are likely in the first week of training? .................................................................. 192
8.2.2 What about muscle activation? ........................................................................................................ 196
8.2.3 What about general strength increases?............................................................................................ 197
8.2.4 Long-term adaptations?................................................................................................................... 198
8.3 SUMMARY ............................................................................................................................. 198
CHAPTER 9: THESIS SUMMARY................................................................................................... 200
9.2 FUTURE RESEARCH ............................................................................................................... 205
REFERENCES..................................................................................................................................... 206
AAPPPPEENNDDIIXX AA...................................................................................................................................... 224499
ETHICS APPLICATION.................................................................................................................. 249
BIOMECHANICAL AND CROSS-SECTIONAL ANALYSIS OF FOUR RESISTANCE TRAINING EXERCISES
..................................................................................................................................................... 249
AAPPPPEENNDDIIXX BB...................................................................................................................................... 225577
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ETHICS APPLICATION.................................................................................................................. 257
INFLUENCE OF MOVEMENT PATTERN OF RESISTANCE TRAINING EXERCISES ON VERTICAL JUMP
AND SPRINT RUNNING PERFORMANCE DURING CONCURRENT RESISTANCE AND TASK TRAINING ... 257
AAPPPPEENNDDIIXX CC...................................................................................................................................... 227700
STATEMENT OF INFORMED CONSENT .......................................................................................... 270
RELIABILITY AND VALIDITY OF ISOMETRIC SQUAT AND FORWARD HACK SQUAT TESTS .............. 270
AAPPPPEENNDDIIXX DD...................................................................................................................................... 227744
TRAINING PROGRAMS ................................................................................................................. 274
EXAMPLE RESISTANCE TRAINING PROGRAMS FOR SQ (SQUAT) AND FHS (FORWARD HACK SQUAT)
GROUPS......................................................................................................................................... 274
AAPPPPEENNDDIIXX FF ...................................................................................................................................... 227777
RELIABILITY STUDY .................................................................................................................... 277
A COMPARISON OF DIGITAL CURVIMETER AND MATHEMATICAL ESTIMATES OF FASCICLE LENGTH
IN CONTRACTING MUSCLE. ........................................................................................................... 277
AAPPPPEENNDDIIXX GG ..................................................................................................................................... 229966
FORWARD HACK SQUAT DATA COLLECTION SCHEMATIC............................................................ 296
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LIST OF FIGURES
Figure 3.1a. The forward hack squat (FHS) exercise was performed in
a semi-prone position by first lowering a sled until the internal knee
angle was approximately 100o................................................................... 64
Figure 3.1b. After lowing the sled it was then moved back to the
starting position in preparation for the next repetition................................ 64
Figure 3.2. The single-leg forward hack squat was performed as per the
double-leg version except that the ‘free’ leg was extended behind the
body in the descending phase and then flexed in the ascending phase.... 65
Figure 3.3. A bar extension was placed on the weighted bar.................. 67
Figure 3.4. Movement pattern of the squat lift exercise........................... 71
Figure 3.5. Movement pattern of the forward hack squat (FHS)
exercise...................................................................................................... 71
Figure 3.6. Movement pattern of the vertical jump................................... 73
Figure 3.7. Movement pattern of the broad jump..................................... 73
Figure 3.8. Comparison of the jump-squat (JSQ) and squat lifts with
60% (SQ + 60%) and 140% (SQ + 140%) of bodyweight across the
shoulders................................................................................................... 75
Figure 3.9. Comparison of single-leg forward hack squat (FHS 1L) and
forward hack squats with 60% (FHS + 60%) and 100% (FHS + BW) of
bodyweight added to the sled.................................................................... 75
Figure 3.10. Comparison of the vertical jumps with arms across the
chest (VJ ac) and with arm swing (VJ wa)................................................. 77
Figure 3.11. Comparison of single-leg broad jump (BJ 1L), broad jump
with arms across the chest (BJ ac) and broad jump with arm swing (BJ
wa)............................................................................................................. 77
Figure 3.12. Comparison of the vertical jump with arms across chest
(VJ ac) and jump-squat (JSQ)................................................................... 79
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Figure 3.13. Comparison of forward hack squat with a load equal to
bodyweight added to the sled (FHS + BW) and broad jump with arms
across the chest (BJ ac)............................................................................ 79
Figure 3.14. Comparison of vertical jumps with arm swing (VJ wa) and
vertical jumps with arms across chest (VJ ac)........................................... 80
Figure 3.15. Comparison of the jump-squat (JSQ) and vertical jump
with arms across chest (VJ ac).................................................................. 81
Figure 3.16. Comparison of joint angle changes for the forward hack
squat (FHS) and acceleration phase of a sprint run (adapted from
Jacobs & Ingen Schenau, 1992)................................................................ 82
Figure 4.1. Subject position for both the isometric squat and forward
hack squat tests......................................................................................... 89
Figure 4.2. Scatterplots of isometric versus 1-RM test performance....... 96
Figure 6.1. Body position for VJ showing cable (to position transducer)
and belt...................................................................................................... 114
Figure 6.2. Position for isometric squat test............................................. 115
Figure 6.3. Position for the isometric forward hack squat (IFHS)............ 117
Figure 6.4. Scatterplots of isometric force produced during a squat
(Squat force isom.) and force during a squat with a load of 60% of
maximum isometric load (Squat force 60%) against VJ height....... 120
Figure 6.5. Scatterplots of isometric force produced during a forward
hack squat (FHS isom.) and force during a FHS with a load of
40% of maximum isometric load (FHS force 40%) against 20 m
sprint time........................................................................................ 122
Figure 7.1. Overview of training and testing............................................. 132
Figure 7.2. The muscle-tendon juntion of rectus femoris was
determined by moving the scanning head (ultrasound) distally along the
thigh........................................................................................................... 136
Figure 7.3. Muscle thickness, pennation and fascicle length estimates
were made at two sites of the rectus femoris and vastus lateralis muscle
using ultrasound......................................................................................... 137
Figure 7.4. Single-leg forward hack squat................................................ 142
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Figure 7.5. Change in muscle thickness for all muscle sites.................... 152
Figure 7.6. Change in muscle pennation for all muscle sites................... 154
Figure 7.7. Change in fascicle length for all muscle sites........................ 176
Figure 7.8. Change (±95% CI) in normalised EMG for five thigh
muscles during the acceleration phase of a sprint run............................... 159
Figure 7.9. Change (±95% CI) in normalised EMG for five thigh
muscles during the performance of a vertical jump................................... 161
Figure 8.1. Hypothesised time course of muscular (A) and neural (B)
changes with resistance exercise.............................................................. 199
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LIST OF TABLES
Table 2.1. Myosin Heavy Chain isoforms in human skeletal muscle........ 42
Table 2.2. Contractile protein isoforms (not including MHC) in human
skeletal muscle......................................................................................... 43
Table 3.1. Landmark names and marker positions for reflective
markers..................................................................................................... 59
Table 3.2. Camera settings during data acquisition................................ 60
Table 3.3. Description of vertical jump techniques.................................. 61
Table 3.4. Description of broad jump techniques.................................... 62
Table 3.5. Body segment definitions....................................................... 66
Table 3.6. Joint angle definitions............................................................. 66
Table 4.1. Reliability statistics for ISQ and IFHS..................................... 94
Table 4.2. Pearson’s correlations for test performances......................... 95
Table 5.1. Mean (±SD) force produced during each trial......................... 106
Table 5.2. Reliability statistics for force produced during dynamic
forward hack squat trials........................................................................... 107
Table 6.1. Mean performance (±SD) for those variables selected for
analysis..................................................................................................... 119
Table 6.2. Significant correlation coefficients (p<0.01) for performance
data........................................................................................................... 120
Table 6.3. Results of factor analysis........................................................ 121
Table 7.1. Details of electrode placements on the five thigh muscles..... 140
Table 7.2. Pre-training, post-training and change scores for sprint, VJ,
FHS and SQ tests..................................................................................... 148
Table 7.3. Reliability statistics for angle of peak torque.......................... 149
Table 7.4. Angle of peak torque (0o = full extension) pre- and post-
training...................................................................................................... 150
Table 7.5. Mean (±SD) pre- and post-test muscle thickness and
change in thickness.................................................................................. 151
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Table 7.6. Mean (±SD) pre- and post-test muscle pennation and
change in pennation.................................................................................. 153
Table 7.7. Mean (±SD) pre- and post-test estimated fascicle length and
change in fascicle length........................................................................... 155
Table 7.8. Results of correlation analysis on pennation and estimated
fascicle length changes after training........................................................ 157
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LIST OF ABBREVIATIONS
Abbreviation Description
1-RM One repetition maximum
A/D Analog to digital conversion
APT Angle of peak torque (isokinetic)
BF Biceps femoris
BJ Broad jump
BJ 1L Broad jump with one leg (unilateral BJ)
BJ ac Broad jump with arms crossed over the chest
BJ wa Broad jump with arm swing
BW Body weight
C7 7th Cervical vertebra
CI Confidence interval (95%)
EMG Electromyography
ES Effect size statistic
FHS Forward hack squat exercise, or a group of subjects who
performed forward hack squat training
FHS 1L Forward hack squat with one leg (unilateral FHS)
FL Fascicle length
FM Fictional muscle
GL Gluteus maximus
HF Hip flexor (superficial to psoas major muscle)
ICC Intra-class correlation coefficient
IFHS Isometric forward hack squat
ISQ Isometric squat
JSQ Jump squat
MU Motor unit
RF Rectus femoris
RF d Distal rectus femoris
RF p Proximal rectus femoris
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RT Resistance training
SD Standard deviation
SEE Standard error of the estimate (measure of error in regression)
SJ Sprint/jump group, a group of subjects who performed sprint and
jump training but no resistance training
SQ Free-weight barbell squat lift, or a group of subjects who
performed squat training
T Thickness of a muscle
TMJ Temporomandibular joint
VJ Vertical jump (countermovement)
VJ 1L Vertical jump with one leg (unilateral VJ)
VJ ac Vertical jump with arms crossed over the chest
VJ wa Vertical jump with arm swing
VL Vastus lateralis
VL d Distal vastus lateralis
VL p Proximal vastus lateralis
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AABBSSTTRRAACCTTSS
xiv
STUDY ONE: A COMPARISON OF MOVEMENT PATTERNS OF THE
VERTICAL JUMP, BROAD JUMP AND ACCELERATION PHASE OF THE
SPRINT RUN TO THE SQUAT LIFT AND FORWARD HACK SQUAT
EXERCISES.
The first purpose of this study was to describe and compare the movement
patterns of athletic subjects performing vertical jump (VJ), standing broad jump
(BJ), squat lift (SQ) and jump-squat (JSQ) tasks. The term ‘movement pattern’
will be used to describe the timing and magnitude of joint angle changes (with
reference to angular velocities and accelerations), body position and laterality of a
movement. A second purpose was to compare the movement patterns of a new
exercise, named the forward hack squat (FHS), and the acceleration phase of a
sprint run. Eight athletic, weight-trained male subjects (age [±SD] = 25.1 ± 2.5
yrs, height = 1.81 ± 0.09 m, weight = 96.3 ± 10.0 kg) performed a standard warm-
up including five minutes of stationary cycling at a self-selected workload and
three to five trials each of a VJ, BJ, SQ with a load of 60% of bodyweight and FHS
with no load added to the sled (the FHS is described later). After reflective
markers were placed on joint centres of the head, trunk and limbs, subjects
performed three maximal trials of single- and double-leg vertical and standing
broad jumps with their arms in different positions, squat lifts and jump-squats with
different loads, and single- and double-leg FHS with different loads. The
movements were recorded by a high-speed video system (200 Hz) and data sets
relating to joint movement (joint angular displacement, velocity and acceleration)
were calculated after digitising joint markers using Peak Motus software (Peak
Performance Technologies, USA).
For all exercises studied, the timing of joint angle changes was the same during
the descending phase with hip, knee and ankle joints flexing (dorsiflexion at the
ankle) simultaneously. However, joint extension during the ascending phase was
different between the tasks. Joint extension occurred sequentially for the VJ, BJ
and JSQ exercises with hip extension preceding both knee and ankle
xv
(plantarflexion) extension. For the slower squat lifts (SQ) joint extensions
occurred simultaneously. The FHS was performed differently to these however in
that hip and knee extension occurred simultaneously with ankle plantarflexion
delayed. The use of an arm swing during VJ and BJ exercises caused the hip
angle to become smaller (more closed) at the end of the transition phase possibly
allowing greater use of the larger hamstring, gluteal and erector muscles. VJ’s
performed without arm swing exhibited the same joint changes as the JSQ
exercise but there were differences in hip joint range of motion between the two
exercises when the arms used.
From these results it was concluded that the joint angle changes of subjects
performing the VJ without arm swing were similar to that of the JSQ. The two
tasks are also performed bilaterally and in a vertical body position, thus their
movement patterns can be considered comparable. However the movement
patterns of the BJ and FHS were dissimilar with the timing of joint angle changes
being different. Joint angle changes for the FHS were then compared to
published data for the acceleration phase of sprint running (Jacobs & Ingen
Schenau, 1992). There was good agreement in the timing and magnitude of joint
angle changes for these two tasks. Given both exercises are performed with the
body in a semi-prone position and the FHS can be performed unilaterally, the
movement patterns of these two exercises could also be considered comparable.
xvi
STUDY TWO: RELIABILITY AND VALIDITY OF TWO ISOMETRIC SQUAT
AND FORWARD HACK SQUAT TESTS
Given the results of Study One, the FHS and SQ exercises were chosen for use in
training and testing in this thesis. However, performing 1-RM tests for the
purposes of assessing performance or designating training loads can be a long
process. It would therefore be ideal to use simpler isometric tests for these
purposes. The aim of this study was first to examine the reliability of isometric
squat (ISQ) and isometric forward hack squat (IFHS) tests to determine if
repeated measures on the same subjects yielded reliable results, and second to
examine the relationship between isometric and dynamic measures of strength to
assess validity. Fourteen male subjects (age range = 19 – 26 yrs) performed
maximal ISQ and IFHS tests on two occasions and 1-RM SQ and FHS tests on
one occasion. The two tests were found to be highly reliable (ICCISQ = 0.97 and
ICCIFHS = 1.00). There was a strong relationship between average ISQ and 1-RM
squat performance, and between IFHS and 1-RM FHS performance (rSQ = 0.77,
rFHS = 0.76; p<0.01) but a weak relationship between squat and FHS test
performances (r<0.55). There was also no difference between observed 1-RM
values and those predicted by our regression equations. Errors in predicting 1-
RM performance were in the order of 8.5% (SEE = 13.8 kg) and 7.3% (SEE =
19.4 kg) for ISQ and IFHS respectively. Correlations between isometric and 1-RM
tests were not of sufficient size to indicate high validity of the isometric tests.
Together the results of the present study suggest that ISQ and IFHS tests could
detect small differences in multi-joint isometric strength between subjects, or
performance changes over time, and that the scores in the isometric tests are well
related to 1-RM performance. However, there was a small error when predicting
1-RM performance from isometric performance so these tests probably cannot
discriminate between small changes in dynamic strength. The weak relationship
between squat and FHS test performance can be attributed to differences in the
movement patterns of the tests.
xvii
STUDY THREE: RELIABILITY OF UNILATERAL AND BILATERAL
FORWARD HACK SQUAT TESTS
The purpose of this study was to examine the reliability of complex, dynamic
unilateral and bilateral FHS tests and determine whether the loads lifted during the
tests affected their reliability. Eleven active, male subjects (age = 20.5 ± 1.1 yrs)
performed two maximal repetitions of a FHS at each of two loads (loads equal to
40% and 70% of maximal isometric force were added to the sled of the machine)
in both uni- and bilateral conditions. Reliability of both uni- and bilateral tasks was
high (ICC = 0.90 and 0.95 respectively) when the heavier load was lifted (70% of
isometric maximum). However, when the load was lighter (40% of isometric
maximum) reliability was low (ICC = 0.70 and 0.64 for unilateral and bilateral trials
respectively). Thus, while the laterality of movement did not affect task reliability,
the load lifted did. The most likely explanation for this result is that the greater
load promotes greater kinaesthetic feedback from muscle spindles, golgi tendon
organs and pacinian corpuscles to the spinocerebellum. In addition, subjects
displayed a bilateral deficit; a phenomenon that has been shown in past research.
This result indicates that the uni- and bilateral tests were measuring different
entities. Thus, testing should be performed according to the type of strength that
must be measured (unilateral or bilateral).
xviii
STUDY FOUR: PERFORMANCE RELATIONSHIPS BETWEEN VERTICAL
JUMP, SPRINT RUNNING AND STRENGTH TRAINING EXERCISES:
IMPLICATIONS FOR MOVEMENT SPECIFICITY
The results from Study One suggested that two pairs of tasks, 1) JSQ and VJ
(with arms crossed over the chest), and 2) FHS and acceleration phase of a sprint
run, were comparable in their movement patterns. The purpose of this study was
to investigate the relationship between subjects’ performances in tests of these
exercises to determine whether movement pattern alone determined performance
similarities between tasks. Thirty-one active subjects including 23 men and eight
women who volunteered from the University population (age range = 18 - 26 yrs)
performed sprint run (20 m), VJ, SQ and FHS tests. Relationships between
subjects’ performances were investigated by both correlation and components
analysis.
Subjects who performed well in the SQ and JSQ tests did not necessarily perform
well in the VJ tests relative to other subjects. However, the FHS and sprint tests,
and the ISQ and VJ tests, were significantly correlated (r = 0.51 – 0.73; p<0.01).
The components (from factor analysis) associated with the VJ and SQ tests, and
the FHS and sprint tests, were different; components could be described by the
force-velocity characteristics of the test exercises. The FHS and sprint tests were
however more similar based on the components under which they were placed.
The FHS may therefore be considered functionally similar to the acceleration
phase of a sprint run when tested under the conditions presented here.
Furthermore, as subjects who performed well in the ISQ also performed well in the
VJ, the two tasks must have some functional similarity. The ISQ requires high
muscle forces over small ranges of motion for optimum performance while high
forces at the eccentric/concentric (downward/upward) transition point in the VJ is
also important. Therefore, the movement pattern and ‘neuromuscular intent’ of
the exercises, but not necessarily their velocity, may have contributed to their
movement specificity. The results have implications for our understanding of
movement specificity.
xix
STUDY FIVE: NEUROMUSCULAR AND PERFORMANCE ADAPTATIONS
TO SHORT-TERM CONCURRENT RESISTANCE AND SPRINT/JUMP
TRAINING.
Given that, for most athletes, resistance training forms only part of a total training
program, it is important that adaptations to resistance training (RT) are described
when task training is performed concurrently. The purpose of this study was first
to determine whether changes in VJ and sprint running test performances after a
period of concurrent resistance- and sprint/jump training were related to the
movement pattern of RT exercises in well-trained subjects. From the results of
studies one and two, and given the known specificity of adaptations to resistance
training, one might expect that subjects who perform JSQ training would improve
their VJ, while subjects who perform FHS training would improve their sprint, more
than other subjects. A second purpose was to examine changes in the
neuromuscular system when the RT was performed concurrently with VJ and
sprint/jump training.
30 active individuals volunteered from the University population (Age range = 18 –
26 yrs). Of the 30 subjects, 23 (eight women & 15 men) completed the study with
approximately equal numbers of subjects in each of three training groups
(described below). Subjects participated in four weeks of resistance- and
sprint/jump training (familiarisation) prior to a second five-week (specific) training
phase.
Following the four-week familiarisation phase, subjects were divided into three
Familiarisation(4 weeks)
Pre-test Specific training (5 weeks)Four groups: SQ, FHS & SJ
Post-test
Overview of training and testing. A familiarisation phase preceded the five-week‘specific’ training phase. Testing was performed before and after the specific trainingphase.
xx
training groups with male and female subjects distributed equally among the
groups. These groups were labelled squat (SQ), forward hack squat (FHS) and
sprint/jump (SJ) based on their training. All groups performed at least two
sprint/jump sessions per week with SQ and FHS groups also performing two
weight training sessions and SJ two additional sprint/jump sessions each week.
Before and after the five-week specific training phase, subjects performed 20 m
sprint, VJ, SQ, FHS and isokinetic leg extension tests. In addition to these
performance tests, muscle thickness, pennation and fascicle length were
measured at two regions of both the vastus lateralis (VL) and rectus femoris (RF)
muscles and EMG was recorded from leg musculature during performance of VJ
and sprint tasks.
After training, subjects significantly increased their 10 m sprint (p<0.05), single-
and double-leg isometric FHS force (p<0.01), force during a double-leg FHS at
40% of isometric maximum, and force during a squat at 30% of isometric
maximum (p<0.05). However, there were no significant differences between the
training groups. This suggests that the five-weeks of training was sufficient to
cause performance changes, but that the training did not result in inter-group
differences. There was also no difference in isokinetic knee extension torque at
either 30o.s-1 or 180o.s-1 but there was a trend toward SQ subjects producing their
torque at a more closed knee angle compared to FHS (ES = 0.71) and SJ (ES =
0.90) subjects. Thus there was a trend toward angle-specific torque changes with
the angle of peak torque decreasing for SQ subjects but increasing for FHS
subjects.
Muscle architectural changes were different between the training groups. In
general, subjects who performed resistance training (SQ and FHS) showed
greater pennation and shorter fascicle lengths (used as an estimate of fibre
length) in VL, while the opposite was true for SJ subjects. For RF, pennation
increased at the distal region in FHS and SQ subjects (p<0.05), but there were no
changes at the proximal region and no significant changes in fascicle length in any
group. Thus for the uni-articular VL architectural adaptations occurred in line with
xxi
those hypothesised. The lack of change in RF might be related to its biarticular
action, muscle length changes are not as great in many multi-joint movements so
the stimulus for adaptation would have been small (Jacobs et al., 1993). There
were significant increases in muscle thickness of both VL and RF although these
changes were not significantly different between the groups. Therefore the
different training regimes performed by the subjects did not differently affect their
muscle thickness.
Changes in normalised EMG during the acceleration phase of running were
inconsistent between subjects. SQ and FHS subjects (results were pooled for
these subjects to increase statistical power) exhibited greater gluteus maximus
activation during the recovery part of the stride and greater biceps femoris, vastus
lateralis and rectus femoris activity immediately prior to foot-ground contact. Such
changes may not be conducive to efficient running. There were few changes for
SJ subjects. For VJ, decreased activity of rectus femoris in the descending phase
and increased gluteus maximus in the transition phase in SQ and FHS subjects
were hypothesised to aid jump efficiency and power. Again there were few
changes in the EMG of SJ subjects. Thus RT appeared to influence EMG and
therefore possibly inter-muscular coordination, particularly in SQ and FHS
subjects. There were however no significant changes in muscle co-contraction
during the sprint or changes in muscle onset times (i.e. time at which muscle
activity significantly increased) during the VJ.
The results of this study suggest that VJ, sprint and strength changes to short-
term concurrent training are not as specific to training as when RT is performed
alone. There were no significant differences in changes in strength, VJ and sprint
performance, and few changes in isokinetic test variables between the groups.
There were however significant changes in muscle architecture that appeared
related to the training performed by subjects. Furthermore, although the EMG
recordings do not provide conclusive evidence that inter-muscular coordination
changed with training, some changes were seen. It appears that, at least in the
short term, similar gains in strength and speed can be attained by different training
xxii
regimes. However there were significant muscular, and evidence for neural,
adaptations to the training. Thus, perhaps in the long-term, the movement pattern
of training exercises and the proportion of low-velocity strength training in a
regime might affect athletic performance and this should be followed up in future
training studies.
1
CCHHAAPPTTEERR 11:: DDeevveellooppmmeenntt ooff
tthhee PPrroobblleemm
2
1.1 INTRODUCTION
Resistance training (RT) is an important component of training for athletes who
require speed, power or strength to successfully compete in their sport. For
example, many sprint runners perform resistance exercises concurrently with their
running training to improve their speed and maximal power. However, which
resistance training exercises elicit optimum improvements in task performance is
yet to be determined (the term ‘task’ refers to the movement which is the focus for
improvement, for example a sporting movement such as running or jumping).
Evidence suggests that adaptations to training are movement-specific, thus some
authors predict that RT exercises best improve movements when they are similar
to the training exercise (Abernethy et al., 1994; Lindh, 1979; Rutherford et al.,
1986; Thépaut-Mathieu et al., 1988).
Movement specificity encompasses both movement pattern- and velocity-specific
adaptations to training. That is, an exercise may mimic or replicate the ranges of
motion, body positions and types of contraction of a movement (i.e. movement
pattern) and/or mimic the velocity of a movement. Thus, movement-specific
adaptations refer to the neuromuscular and performance adaptations to an
exercise of a specific movement pattern and velocity.
With respect to movement pattern specificity, it has been shown that adaptations
to RT depend on several ‘factors’. These include the body position adopted
(Raasch & Morehouse, 1957; Wilson et al., 1996), the muscle lengths and joint
angles through which work is performed (Kitai & Sale, 1989), whether training is
performed unilaterally or bilaterally (Tanaguchi, 1997) and the types of
contractions and precontractions used (e.g. eccentric, concentric, isometric, rapid
pre-stretch, etc.; Hortobágyi et al., 1996; 2000) during training. The mechanisms
responsible for such training effects are unclear. Evidence from research
investigating a neural basis for movement pattern specificity is contradictory in its
conclusions (i.e. changes in muscle co-contraction and timing of muscle
3
recruitment, e.g. Weir et al., 1994, 1995b) while little research has examined
muscular changes such as sarcomere length-tension characteristics (Koh, 1995).
From a more practical standpoint, research investigating movement pattern-
specific adaptations to RT has proffered as many questions as it has answered.
For example, it is unclear how similar movement patterns of a task must be to a
resistance exercise for optimum improvement, whether the movement patterns of
resistance exercises must be similar to the sporting task when both resistance-
and task training are being performed concurrently in a training regime, and
whether it is necessary to consider all factors of movement pattern specificity for
optimal improvements in sporting performance. Moreover, most studies
investigating movement pattern-specific adaptations to RT have used untrained or
‘active’ subjects (e.g. Delecluse et al., 1995; Narici et al., 1989; Sleivert et al.,
1995; Young & Bilby, 1993). Given that the propensity for adaptation of well-
trained or elite athletes could be different to that of untrained individuals (Häkkinen
et al., 1987) the results of research using untrained subjects may not predict the
adaptation process of well-trained athletes. Thus, research involving well-trained
subjects is necessary to establish the necessity for movement pattern-specific
resistance training when task training is performed concurrently. It is also
necessary to determine whether some ‘factors’ affecting movement pattern-
related adaptations are more important than other factors.
With respect to the velocity specificity of adaptations to RT, results of studies
investigating responses to isokinetic training suggest that strength increases are
greater at, and perhaps below, the movement velocities of the training exercises
(Caiozzo et al., 1981; Petersen et al., 1989). When an isotonic (isoinertial)
training mode is used, subjects who trained using higher-velocity movements
tended to perform better in tasks requiring higher movement speeds (Wilson et al.,
1993). These velocity-specific adaptations have been considered a reflection of
many neuromuscular changes. Changes in the nervous system are thought to
include increases in total muscle recruitment (Häkkinen and Komi, 1983, 1985,
1986; Häkkinen et al., 1985b), an increase in the firing frequency of motor units
4
(Behm & Sale, 1993b), a selective activation of fast-twitch fibres (Grimby &
Hannerz, 1977; Nardone et al., 1989) which may be more likely during the
performance of complex movements (Behm & Sale, 1993b), and the selective
recruitment of muscles containing a high fast-twitch fibre content (Duchateau et
al., 1986; Nardone & Schieppati, 1988). Muscular changes might include fibre
type transformation toward fast-twitch fibres (Jansson et al., 1990), changes in
sarcomere contractile kinetics (Behm & Sale, 1993b), and increases in muscle
fibre length (Sacks & Roy, 1982; Kumagai et al., 2000).
Despite research showing movement-specific adaptations to RT, many athletes
who perform resistance training concurrently with training for their own sport (task
training) use resistance training exercises of low movement velocities that are
often not similar in movement pattern to the task they wish to improve. Such
training methods are a result of anecdotal evidence from coaches and athletes
that good improvements in task performance are achieved by increasing ‘general’
strength by resistance training and then ‘transferring’ the strength by performing
task training. Furthermore, adaptations to resistance training have been reported
to have both a positive (Bell et al., 1989; Smith & Melton, 1981; Wilson et al.,
1996) and negative (Barrata et al., 1988; Behm & Sale, 1993b; Tesch & Larson,
1982) impact on high-speed task performance. As such it is unclear whether
resistance training, even at higher movement velocities, is beneficial to athletes
requiring high-velocity force production despite its accepted use as a training tool.
In summary, adaptations to resistance training appear to be specific to both the
movement pattern and velocity of the training exercises. Furthermore, some
research has highlighted possible disadvantages of weight training even when its
movement characteristics are similar to the sporting task. Given the disparity
between the ‘theoretically correct’ movement-specific resistance training and that
often performed by athletes, more research is needed to determine whether
resistance training is a useful addition to a training regime and whether the
movement characteristics of the resistance training must be similar to the sporting
task for optimum improvements to occur.
5
1.2 PURPOSE
There are a number of specific aims of this thesis:
1. To examine the movement patterns of the squat lift (SQ) and forward hack
squat (FHS; a new exercise) exercises in order to describe the body position,
joint angle changes and the timing of these changes, and laterality. Then
compare these to the movement patterns of the vertical jump (VJ), broad jump
(BJ) and sprint start (the technique used during the running acceleration phase
of sprinting).
2. To determine the reliability of isometric forward hack squat (IFHS) and squat
(ISQ) tests and their relationship to a dynamic (1-RM) versions of the same
exercise. This information will be used to determine whether isometric
versions of the exercises can be performed to estimate subject’s dynamic 1-
RM’s and predict training loads for a longitudinal (training) study.
3. To assess the reliability of uni-lateral and bilateral FHS tests under different
loading conditions.
4. To investigate the relationship between VJ and 20 m sprint performance and
the forces produced during maximal SQ and FHS lifts in a cross-sectional
analysis using well-trained athletes.
5. To examine the effects of different resistance training exercises on sprint and
jump performance in athletes who perform identical running acceleration and
VJ training.
6. To identify neuromuscular changes that are responsible for movement pattern-
and velocity-specific adaptations to concurrent resistance and task training.
7. To formulate a theory that can explain the adaptation process of the
neuromuscular system to concurrent resistance and task (e.g. VJ, sprint, etc.)
training using evidence gained from this research to substantiate some parts of
that theory.
6
1.3 SIGNIFICANCE OF STUDY
While research has shown that adaptations to RT are specific to the movement
pattern adopted, it is not yet clear which components of a task’s movement
pattern should be replicated when performing RT to achieve optimal improvement
in that task: body position, muscle lengths and joint angles, laterality (i.e. left limb,
right limb or both trained simultaneously), type of contraction, or type of pre-
contraction. It is also unclear whether the velocities of RT movements need to
approach task velocity and whether adaptations to RTare still specific to both
movement pattern and velocity when RT is combined with task training. This
contention is largely due to the majority of research examining the adaptations to
resistance training in subjects who are not performing task training concurrently.
This research will provide an insight into the importance of replicating body
position, joint angle changes and laterality (types of contraction and pre-
contraction will be similar between the RT and task movement patterns so their
effects cannot be evaluated) during RT for optimum improvement in dynamic task
performance. Furthermore, the adaptations that occur when RT is performed with
task training (the term ‘task’ refers to the movement trying to be improved) will be
compared to those adaptations that take place with task training alone.
Particularly, I will describe a new exercise (the FHS) which has been designed to
allow subjects to move with similar movement patterns to the acceleration phase
of a sprint run. This series of studies will also help determine whether adaptations
to resistance training are specific to movement pattern and velocity when it is
performed concurrently with task practice. They will similarly provide an insight
into the neuromuscular adaptations to concurrent resistance- and task training.
Past research has speculated, rather than defined, adaptations to such training
(e.g. Delecluse et al., 1995). Importantly, well-trained subjects will be used as
subjects in this study so that the results are more applicable to competitive
athletes. Therefore the results will assist coaches design training programs to
enhance athletic performance.
7
1.4 OVERVIEW OF STUDIES
1.4.1 STUDY ONE
Tasks such as the VJ, BJ and sprint run are commonly performed in many sports,
as well as in studies investigating human performance. Given that adaptations to
RT are specific to the movement patterns of training exercises (Abernethy et al.,
1994; Rutherford et al., 1986; Wilson et al., 1996) it might be important that
training exercises aiming to improve these tasks, and tests designed to assess
performance, have similar movement patterns to the tasks. As there is limited
data comparing common resistance and task exercises, the main purpose of the
first study was to describe and compare the movement patterns of athletic
subjects performing VJ, BJ, SQ and jump-squat (JSQ) tasks. A second purpose
was to compare the movement patterns of a unique exercise, named the forward
hack squat (FHS; see Figure 3.1), and the acceleration phase of a sprint run. The
FHS exercise was designed to allow subjects to train with a movement pattern
similar to the acceleration phase of a sprint run. Due to space limitations in the
biomechanics laboratory at Southern Cross University the sprint run could not be
properly analysed and the kinematics of the FHS were compared to sprint running
data published by Jacobs and Ingen Schenau (1992).
1.4.2 STUDY TWO
Given the results of Study One, the FHS and SQ exercises were chosen for use in
training and testing in this thesis. However, performing 1-RM tests for the
purposes of assessing performance or designating training loads can be a long
process. It would therefore be ideal to use simpler isometric tests for these
purposes. The aim of this study was first to examine the reliability of isometric
squat (ISQ) and isometric forward hack squat (IFHS) tests to determine if
repeated measures on the same subjects yielded reliable results, and second to
8
examine the relationship between isometric and dynamic measures of strength
to assess validity.
1.4.3 STUDY THREE
Given the FHS is a new exercise and will be used to assess performance changes
with training it was important to establish its test-retest reliability. The purpose of
this study was to examine the reliability of complex, dynamic unilateral and
bilateral FHS tests and determine whether the loads lifted during the tests affected
their reliability.
1.4.4 STUDY FOUR
While Study One aimed to show which resistance- and performance tasks were
similar in their kinematics, it was still unclear if subjects who performed well in a
resistance task also performed well in its associated performance task. In order to
more clearly determine which resistance and task movements were most similar
in their movement characteristics the relationship between subjects’ performances
in the squat lift, FHS, vertical jump (VJ) and 20 m sprint tests was determined. It
was hypothesised that subjects should perform equally well in tests where the
movements were similar.
1.4.5 STUDY FIVE
The results of studies one and four provided information regarding the kinematics
of, and performance relationships between, the squat, FHS, VJ and 20 m sprint.
From this, it was evident that subjects exhibited similar movement patterns during
the FHS and sprint tests. Furthermore, relative to other subjects in the studies,
subjects who performed well in the FHS also performed well in the sprint run.
Similar movement patterns were also shown for the VJ and jump squat (JSQ)
9
exercises. While a slightly better performance relationship was seen between
the ISQ and VJ, subjects who performed well in the VJ tests seemed also to
perform well in the SQ tests. Given the information from the two studies, it was
hypothesised that if adaptations to RT were specific to the movements used in
training greater performance benefits would possibly be seen in the sprint after
FHS training while greater improvements in the VJ might be seen after squat (or
JSQ) training.
Since most athletes perform RT concurrently with task training, a longitudinal,
concurrent training study (Study Three) was undertaken. The first purpose this
study was to determine whether changes in VJ, sprint run and strength tests were
related to the movement patterns of multi-joint, dynamic RT in well-trained
subjects. The second purpose was to compare neuromuscular and performance
changes when the VJ and sprint training (i.e. task practice) was performed by
itself or concurrently with RT.
10
1.5 LIMITATIONS
While the conclusion was made from Study One (Chapter 3) that the movement
patterns of the forward hack squat (FHS; see Figure 3.1) and acceleration phase
of sprint running were similar, no statistical comparisons were made because raw
data describing the kinematics of the sprint start were not available (i.e. data from
the FHS were compared to figures presented for the sprint start by Jacobs &
Ingen Schenau, 1992).
The student population of Southern Cross University is small (approx. 7000) so
subject recruitment can be difficult, especially for studies such as those in this
thesis where well-trained subjects were used.
Only a small number of subjects (N = 23) completed Study Five (Chapter 7). This
was due to the small subject number recruited for the study due to the small pool
from which to draw subjects, the necessity to recruit well-trained subjects and also
to drop out from unforseen circumstances. Not only would this reduce the
likelihood of statistically significant findings but increase the risk of type I error.
Subjects in Study Five only trained for 5 weeks (after familiarisation). Therefore,
long-term adaptations to such training are difficult to estimate. A longer training
period was not possible given a long holiday period between semesters. This
would have made monitoring subject training unreasonably difficult.
While subjects in Study Three were asked to ‘continue their normal training while
ceasing any RT that was not part of the study’, this was difficult to monitor.
Therefore, training performed outside this research may have influenced the
results.
Changes in the nervous system after training in Study Five were investigated
using surface electromyography. While cross-talk would have been minimal given
11
the large muscles over which electrodes were placed (approximate pick-up
area � 20 mm; Barkhaus & Nandedkar, 1994; Fuglevand et al., 1992; Lynn et al.,
1978). There are inherent limitations to surface electromyography in dynamic
contractions (e.g. changes in muscle length affect EMG wave forms; Okada,
1987) and there is diffuculty in determining longitudinal changes in muscle
recruitment.
1.6 DELIMITATIONS
While the subjects used in Study Five were classed as ‘well-trained’, their training
histories were not similar. Training programs for different sports differ to suit the
characteristics of the sport. A four-week familiarisation phase was included to
ensure some of the training performed by the subjects in the lead up to the
training study (Study Five) was similar. However, it is difficult to classify these
subjects and delimit the results of this thesis. Nonetheless, it can be assumed
that the results can only be directed at healthy, athletic men and women of the
age range 18 – 35 years.
While the concurrent training regimes used in Study Three were designed to
assess the effects of concurrent resistance and speed training on physical
performance, many athletes perform different regimes. The number and intensity
of resistance- and task training sessions performed by athletes varies
independently. The results of the present thesis provide some insight as to what
adaptations could occur with concurrent training regimes, but it is unclear what
adaptations occur to other regimes.
12
CCHHAAPPTTEERR 22:: LLIITTEERRAATTUURREE
RREEVVIIEEWW
13
2.1 INTRODUCTION
The literature relating to movement pattern- and velocity-specific performance
adaptations to resistance, sprint and concurrent training, the neuromuscular
adaptations to such training, and the neuromuscular principles that govern human
movement (i.e. force-velocity and torque-angle relationships, energy kinetics of
muscular contraction, principles of stretch-shorten movements, coordination of
complex movements, etc.) is vast. The purpose of the present literature review is
not to discuss all aspects of neuromuscular and musculoskeletal function but to
provide a synopsis of research into the movement pattern- and velocity-specific
adaptations to training, and the possible positive and negative effects of
resistance training per se. This will further highlight the necessity of the present
research.
Each of the three separate studies described in this thesis has its own introduction
in which important concepts and scientific findings that are relevant to that
particular area of study are presented. In this literature review, research
examining movement-pattern specific adaptations to resistance training will be
presented with some discussion as to the mechanisms that might cause such
changes. Further, literature documenting velocity-specific performance
improvements from resistance training (RT) and the mechanisms responsible for
this specificity will be reviewed. Finally, a short discussion of the possible positive
and negative effects of resistance training on movement performance will be
presented. It will highlight many of the dilemmas faced by athletes and coaches
trying to determine the optimum combination of resistance- and task training in a
concurrent training regime.
14
2.2 EFFECT OF RESISTANCE TRAINING MOVEMENT PATTERN ON
TASK PERFORMANCE
Research investigating the movement pattern-specific adaptations to RT has
focussed on several factors, including: 1) body position, 2) muscle lengths and
joint angles, 3) unilateral and bilateral specificity, 4) type of contractions, and 5)
type of pre-contractions. All of these factors have been shown to influence
strength adaptations and may affect both the movement pattern- and velocity-
related changes that occur with RT.
2.2.1 Body position
Body position refers to the orientation of the body relative to a reference plane and
is often described by terms such as supine, prone, standing, seated, lying,
recumbent, curled and flat. In one of the first studies of the influence of body
position on strength adaptations, Raasch and Morehouse (1957) trained subjects
with an elbow flexion exercise while in the standing position. When tested in both
the standing and supine positions, strength increases were significantly greater
when subjects were in the familiar, standing position. Later, Solomonow et al.
(1986), studying the activity patterns of the elbow flexor and extensor muscle
groups, reported a change in antagonist activity between different body positions
that may have been a compensation for the change in body orientation relative to
gravity. Thus, the findings of Raasch and Morehouse (1957) were supported by
this work.
More recently, Abernethy and Jürimäe (1996) reported differences in subjects’
triceps strength when testing was performed using a triceps test similar to that
used in training and an unfamiliar test. After performing standing triceps
pushdown, close-grip bench press and triceps kickback exercises, the rate of
change in standing triceps pushdown strength differed to strength in the unfamiliar
supine triceps extension exercise. Furthermore, the result of a factor analysis
15
indicated that strength in these tasks were associated with different factors in
three of four testing occasions over the 12 weeks of training. Thus the body
position adopted during training may have influenced strength adaptations.
Wilson et al. (1996) found that subjects who performed bench press training
improved significantly in a bench press throw (8.4%) but not in a push-up test
(0.7%). The push-up test was performed at a similar movement velocity and with
similar kinematics, but in an inverted position (i.e. the force was directed
downward rather than upward). It is therefore likely that body position was the
factor that most notably affected the adaptation to training. Thus, research
investigating strength and performance improvements after a period of weight
training has shown strength improved most notably in exercises where the body
position adopted was similar to that of the training exercise. Strength gained by
training in one body position may therefore not completely transfer to strength
improvements in another (Raasch & Morehouse, 1957; Wilson et al., 1996).
2.2.1.1 Mechanisms responsible for body position-specific performance
changes
The mechanisms responsible for the body position-specific training response have
not been extensively researched. However, it is possible that different postures
are associated with different muscle or motor unit recruitment strategies.
Solomonow et al. (1986) found differences in antagonist activity between elbow
flexor and extensor muscle groups with different body orientations. Such changes
were hypothesised to compensate for differences in the influence of gravity
between the body positions. Person (1974) reported changes in the recruitment
order of rectus femoris motor units as the posture of a task was changed from a
‘fixed’ to a ‘free’ condition. A difference in the direction of force application that
occurred in response to the change in posture may have contributed to this
change in neural drive. Also, muscles with similar actions show different levels of
activation (Mao et al., 1996) and the frequency content of their myoelectric signals
change (Signorile et al., 1994) depending on the task performed. Motor units of
16
the same muscle have also been shown to be recruited differently depending
on the direction of force application (Ter Haar Romeny et al. 1982, 1984). These
findings suggest that the nervous system used different strategies to activate
muscles when the body position was changed. It is likely that adaptations in the
nervous system to resistance training depend on the body positions adopted.
However these neural adaptations are not well understood.
No research has investigated muscle architectural adaptations (i.e. orientation of
fibres, length of fibres, etc.) to training in different body positions. The effects of
gravity would be different in different body positions that would alter the force
magnitude and direction requirements of a muscle. The magnitude and direction
of forces produced by muscles are influenced by their architecture, particularly in
pennate muscles; indeed many different types of pennate muscles exist and each
has different force generating properties. Changes in the angle of the
aponeurosis (the extension of the tendon that passes through the muscle and
onto which fibres attach) relative to the tendon, angle of fibres to the aponeurosis,
and heterogeneity of within-muscle fibre arrangements might have some effect on
the magnitude and direction of force production. Research examining changes in
architecture after training is required before the relationship between architecture
and body position-specific strength changes can be described.
2.2.2 Joint angles and muscle lengths
Many researchers have examined the training-induced increase in force at one
joint angle or muscle length to force produced at another joint angle or muscle
length (Kitai & Sale, 1989; Lindh, 1979; Weir et al., 1994). Most of the research
has referred to the effects of manipulating the joint angle, rather than muscle
length per se, on strength adaptations during resistance training. Changes in the
length of muscles crossing a joint do not directly accompany changes in joint
angle since the moment arm of the muscle-tendon unit often varies as the joint
angle changes (Nemeth & Ohlsen, 1987; Visser et al., 1990). Nonetheless, for
single-joint tasks at least, the length of the muscle-tendon unit is usually
17
determined by the joint angle. For example, if contraction conditions were held
constant (i.e. force, duration, muscle fatigue, etc.), the muscle-tendon length
would not change between repeated contractions at a particular joint angle. For
the purpose of this literature review therefore, the term ‘joint angle’ will describe
the angle between bones comprising a joint and the corresponding length of the
muscles crossing that joint. Given that most research (e.g. Lindh, 1979; Weir et
al., 1994, 1995a,b) specifically uses only single-joint movement tasks, muscle
length and joint angle will be considered synonymous.
2.2.2.1 Joint angle specificity in isometric contractions
Much research suggests that isometric strength is likely to increase most at and
around the joint angles which strength training is performed (Gardner, 1963;
Belka, 1968; Kitai & Sale, 1989; Lindh, 1979; Weir et al., 1994, 1995b). Early
research by Gardner (1963) showed that significant increases in isometric knee
extensor torque were only seen at the angle at which training occurred. Also,
Lindh (1979) found that isometric strength increased by approximately 30% at the
angle at which training was performed but only 12% at the non-training angle
(angles differed by 45o). Other evidence suggests that there might be a greater
movement pattern-specific effect when training is performed at shorter muscle
lengths (Thepau-Mathieu et al., 1988). Nonetheless, there appears to be angle-
specific performance changes with training.
As yet, few studies have shown non-specific adaptations to resistance exercise.
Much of the research that has not shown clear angle-specific effects required the
subjects training at larger joint angles (and consequently long muscle lengths
[Bandy & Hanten, 1993; Meyers, 1967]). Nonetheless, strength changes have
been shown to be more general when training is performed at such angles
(Thépaut-Mathieu et al., 1988). In all, strength gains are greater for movements
performed at or near the training angle than at very different joint angles when
resistance training is performed in isolation (i.e. not concurrently with other task
training).
18
2.2.2.2 Joint angle specificity in dynamic movements
Much of the research on angle-specific training adaptations has utilised isometric
training to elicit strength gains, so questions could be raised as to the validity of
these results to dynamic training (Wilson & Murphy, 1996). Although the research
on joint angle specificity of dynamic training is sparse, and the specificity of
dynamic training is not conclusive, the same angle-specific adaptations have been
shown after dynamic forms of training. Graves et al. (1989) had one group of
subjects train the knee extensors through a range of motion from 120 - 60o of
flexion, while a second group trained from 60 - 0o of flexion. After the training
period the first group performed significantly better in isometric strength tests
between the angles of 120 and 60o, while the second group performed
significantly better at angles between 60 and 0o of flexion. This suggested that
strength changes after dynamic training were also specific to the joint range of
motion despite the testing and training modes being different (dynamic versus
isometric). The angle-specific training effect however should be examined by
studies utilising dynamic, as opposed to isometric, training and testing modes.
2.2.2.3 Mechanisms underlying the angle-specific effect
Changes within the Central Nervous System – Whole muscle activation and inter-
muscular coordination
No single mechanism has been proven responsible for the angle-specific
adaptations to resistance training, although adaptations within the central nervous
system (CNS) have been implicated. Kitai & Sale (1989) found that voluntary
isometric plantar flexor strength increased only at or near the training angle while
evoked twitch force did not improve at any angle. Thus, joint angle specificity was
only observed during the voluntary contractions. Furthermore, since twitch force
19
did not improve it is likely that the angle-specific strength changes were a result
of changes in neural drive to the agonist muscles. Alternatively, the lack of
strength increases during the twitch condition might suggest that the muscle was
not maximally activated by this method.
Further, results of studies investigating cross-education (a performance
enhancement of a non-training limb after unilateral training) have shown strength
increases in an untrained limb that were similar to the trained limb (Weir et al.,
1994). Such research suggests that changes in hypertrophy and muscle
architecture could not have influenced the torque-angle relationship since there
was no stimulus for such changes. Evidence however that myosin light chain
changes can occur in a ‘control’ limb (Srihari et al., 1981) suggests that such
speculation might not be warranted. Furthermore, cross-education is not always
seen, even after similar training regimes are performed (Weir et al., 1994 versus
1995b).
Some researchers also speculate that changes in co-contraction patterns could be
responsible (Weir et al., 1994). Both increases (Baratta et al., 1988) and
decreases (Carolan & Cafarelli, 1992; Pousson et al., 1999) in muscle co-
contraction have been reported after periods of resistance training. However no
studies have shown that a change in co-contraction patterns occurred
simultaneously with angle-specific strength changes. It is unlikely that changes in
the recruitment of agonist muscles are responsible for angle-specific performance
changes. Much research has shown that changes in muscle recruitment are rare
with resistance training (Brown et al., 1990; Carolan & Cafarelli, 1992; Harridge et
al., 1999, Young et al., 1985). Also, no changes in surface EMG have been
shown after angle-specific training (Weir et al., 1994; 1995b), but angle-specific
strength changes have been found after training involving electrical stimulation of
relaxed muscle (Martin et al., 1994). Thus, despite attempts to attribute angle-
specific changes to a neural origin, no studies have shown a direct link between
changes in muscle recruitment and angle-specific strength.
20
Changes within the Central Nervous System – Changes in intra-muscular
recruitment
Specially grouped motor units may also be involved in movement-specific strength
adaptations. Motor units in many upper body muscles are grouped as sub-
populations or ‘functional compartments’ based on the likelihood of their activation
during a given contraction (Ter Haar Romeny et al., 1982; 1984; Theeuwen et al.,
1994; Tonndorf & Hannam, 1994; Van Zuylen et al., 1988). Little research has
described compartmentalisation of lower limb muscles although fibres of the
gracilis (Schwarzacher, 1959), sartorius (Barrett, 1962; Schwarzacher, 1959) and
the semitendinosus (Barrett, 1962) have been shown not to run the entire muscle
length. This suggests that a similar ‘compartment-based’ organisation to upper
body muscles may be present in lower body muscles in humans.
While the functional significance of compartments has not been studied
extensively in humans, there has been considerable research on animal muscles
(Chanaud et al., 1991; Pratt et al., 1991). Chanaud et al. (1991) showed that the
cat biceps femoris and tensor fasciae latae were comprised of functional
compartments with differential synaptic inputs. Also, Loeb et al. (1987) measured
the EMG evoked by stimulation of the branches of the motor axon to the cat
sartorius muscle and found that each compartment was selectively activated.
Together, these two studies suggest that compartmentalised muscles may in fact
be comprised of small, uniquely-activated musclets. Zuurbier and Huijing (1993)
then discovered that fibres located in different regions of the rat gastrocnemius
medialis reached their optimum (length at which maximum contractile force is
produced) and slack (length at which no passive/elastic force is produced) lengths
at different overall muscle lengths. This suggested that innervation of
compartments may be dependent on fibre lengths, or at least the lengths of
sarcomeres constituting the fibres. Indeed, Van Zuylen et al. (1988) also found
that the recruitment of compartments within the human biceps brachii was
dependent on the joint angle, and therefore the muscle length, at which the
contraction was performed.
21
While not shown experimentally, it is possible that movements that are performed
through different joint angles are associated with different activation patterns of
compartmentalised muscles in a manner related to the length of sarcomeres. One
might expect therefore that a period of muscle length-specific (or joint angle-
specific) RT could promote rapid changes in the length of sarcomeres within
compartments, and possibly the number of sarcomeres within such
compartments. Such adaptations would alter the muscle length-specific (joint
angle-specific) force produced by these muscles.
Changes in the periphery - Sarcomere length/tension adaptation
The length at which sarcomeres produce optimum force varies with their resting
length (Ettema & Huijing, 1994; Gareis et al., 1992; Tabary et al., 1972) and
research has shown that changes in sarcomere length occur within days of
stimulus application (Herbert & Belnave, 1993; Williams, 1990). Furthermore, the
passive length-tension relationship is also altered after sarcomeric changes occur
(Goldspink, 1974; Tabary et al., 1972; Williams et al., 1990). Thus changes in
sarcomere length would influence the length-tension properties of a muscle.
Force stimuli (in the form of electrical stimulation) has been shown to promote
sarcomere changes (Williams et al., 1986). Williams (1990) also showed that only
acute periods of stretch (0.5 hours per day) were necessary to increase the
number of sarcomeres by up to 10% within two hours of the stretch. Lynn and
Morgan (1994) reported that decline running produced more sarcomeres in the rat
vastus intermedius fibres than incline running. Such results suggest that a stretch
(or perhaps force) stimulus need only be applied for short periods for adaptations
to occur.
It has not been confirmed however whether the length of sarcomeres adapts to
the muscle lengths at which resistance training is performed. Nonetheless,
Herring et al. (1984) showed that optimum sarcomere length could adjust to that
22
length where maximum muscle forces are required. Further, data of Weijs and
van der Wielen-Drent (1982, 1983) that was re-analysed by Herring et al. (1984)
predicted that sarcomere length was related most to either the muscle length
halfway between the greatest and least stretched position, or to the position where
maximum force was applied. It is therefore likely that the resting length of
sarcomeres adapts to force stimuli such that the length-tension relationship of its
constituent fibre is optimum when the greatest force is required. Given that
changes in sarcomere length occur rapidly, and well within the time frame of
angle-specific torque changes, such adaptations may be a factor in the angle-
specific response to training.
Changes in the periphery – Muscle pennation
Changes in the angulation of fibres relative to the aponeurosis or tendon
(pennation) could also affect the length-tension characteristics of a muscle.
Certainly muscles with greater pennation have a smaller length over which high
muscle forces can be produced (Kaufman et al., 1989; Wottiez et al., 1983). It is
unclear if this is due to increased pennation or the shortness of fibres associated
with these muscles. However the length at which optimum force is produced
would also be affected by the angle of pennation. Fibres of pennate muscles not
only shorten, but rotate, during muscle shortening (Benninghoff & Rollhauser,
1952; Muhl, 1982). As the angle between the fibres and tendon increases, the
amount of fibre-generated force being directed along the tendon decreases since
the fibres are pulling across rather than in line with the tendon. If fibres produced
the same tension at all lengths, the force generated by a muscle would be related
to the angulation of the fibres, i.e. maximum muscle force would be produced at
the longest muscle lengths. Since muscle fibres have an optimum length for force
development, the muscle length at which optimum force is produced in pennate
muscles would be related to both the fibres’ optimum lengths and the degree of
muscle pennation.
23
2.2.2.4 Summary
Strength changes with resistance training are specific to the joint angles (or
muscle lengths) at which training is performed. This appears true for both
isometric and dynamic movements. The mechanisms by which these changes
occur are not well understood. It is unclear whether sarcomere length changes
occur after a period of joint angle-specific training, whether certain regions within a
muscle are more or less active after training at specific angles, or whether there is
a change in the co-contraction of antagonist muscles after such training. While the
degree of fibre pennation might also affect joint angle-specific strength changes, it
is unlikely that factors such as hypertrophy or changes in the structure or
functioning of the joint itself are important.
2.2.3 Unilateral versus bilateral specificity
The effects of training either uni- or bilaterally have been described by two,
possibly related, phenomena. First, cross education describes an increase in
strength of an untrained limb when the contralateral limb is trained (Cabric &
Appell, 1987; Cabric et al., 1988; Laughman et al., 1983). Second, bilateral deficit
[or facilitation] refers to an effect whereby the maximum force that a muscle can
exert decreases [or increases] when the homologous muscle in the opposite limb
is contracted (Enoka, 1997). Athletes who often perform unilateral tasks (e.g.
cyclists) as well as untrained individuals have been shown to exhibit bilateral
deficit while weightlifters exhibit bilateral facilitation (Howard & Enoka, 1991).
Nonetheless, the bilateral deficit can be reduced (or perhaps reversed) by bilateral
training (Häkkinen et al., 1996; Rube & Secher, 1990; Tanaguchi, 1997) and a
bilateral facilitation can be reduced by unilateral training (Häkkinen et al., 1996;
Tanaguchi, 1997; Weir et al., 1997). These specific changes appear similar for
different exercise tasks (hand grip strength, leg extensor power and arm extensor
power [Tanaguchi, 1997]). However, the bilateral deficit is often greater for high-
speed movements (25-45%; Koh et al., 1993; Vandervoort et al., 1984) than
slower movements (<20%; Howard & Enoka, 1991; Koh et al., 1993). Therefore
24
specificity of training adaptations with respect to laterality exists (i.e. unilateral
versus bilateral training). The phenomenon has particular implications for the
training of athletes since many athletic pursuits are performed with the movement
of one limb (e.g. javelin, long or high jumping, kicking, etc.) or with alternating
limbs (e.g. swimming, running, cycling, etc.).
2.2.3.1 Mechanisms responsible for the bilateral deficit (facilitation)
Some investigations have shown decreases (Howard & Enoka, 1991; Koh et al.,
1993; Ohtsuki, 1983; Vandervoort et al., 1984) and others no change (Häkkinen et
al., 1995; Jakobi & Cafarelli, 1998; Schantz et al., 1989) in surface EMG (used as
a measure of muscle activation) with the force deficit that often accompanies
bilateral movements. The results of twitch interpolation studies are also equivocal
with different muscles showing different degrees of activation depending on
whether the movement was performed uni- or bilaterally (Herbert & Gandevia,
1996). Also Jakobi and Cafarelli (1998) found a large, but not statistically
significant, increase in muscle activation in unilateral movements.
The rate of force development (Koh et al., 1993) and mean power frequencies
(Oda & Moritani, 1994) of muscles activated under bilateral conditions is also less
than when activated unilaterally. This suggests perhaps that neural drive is
diminished in the bilateral condition. Such findings are consistent with decreases
in the H-reflex (i.e. the motoneuron pool is less excitable and associated motor
units less likely to fire) of a non-contracting limb that have been observed when
the contralateral limb is performing a movement (Kawakami et al., 1998).
Research so far suggests it is most likely that a decrease in neural drive is the
cause of force decrements in bilateral contractions.
It is unclear whether other neural changes are responsible. Ohtsuki (1983)
showed greater elbow flexor/extensor co-contraction during bilateral than
unilateral elbow flexion movements, although Koh et al. (1993) observed a
decrease in quadriceps/hamstrings co-contraction during bilateral leg extension.
25
It is unlikely however that increased concentration demands could affect force
produced during bilateral contractions as no bilateral deficit is seen when non-
homologous muscles or muscle groups are contracted (Howard & Enoka, 1991;
Ohtsuki, 1983; Schantz et al., 1989). Thus while some modifications of neural
drive probably occurs between uni- and bilateral movements, the mechanisms
responsible for the bilateral deficit are unclear. It does however seem that specific
adaptation and performance changes occur with uni- and bilateral changes.
2.2.4 Type of contraction
Adaptations to strength training appear to be specific to the type of contraction (ie
concentric or eccentric) performed in training (Hortobágyi et al., 1996, 2000;
Lacerte et al., 1992; Smith & Rutherford, 1995; Tomberlin et al., 1991). Generally,
eccentric training leads to better improvements in eccentric strength than
concentric training. The opposite is true for concentric training. It is unclear
whether eccentric or concentric training improves isometric strength the most with
some studies showing greater increases with concentric (Hortobágyi et al., 1996,
2000) but others eccentric (Smith & Rutherford, 1995) training. Therefore, while
some studies provide evidence that adaptations to training may not depend on the
type of contraction (Petersen et al., 1991; Singh & Karpovich, 1976), it is
anticipated that strength gains resulting from resistance training are specific to the
type of contraction performed. Unfortunately, only a few studies have investigated
the adaptations to eccentric and concentric isotonic/isoinertial training (Johnson,
1972; Johnson et al., 1976; Komi & Buskirk, 1972). The results of these studies
suggest that specificity of contraction type may be similar to that associated with
isokinetic training.
The influence of type of contraction will not be investigated in the present thesis.
However, given the specificity of adaptations to movement type, it will be held
constant between training groups in the training study that will investigate the
effect of movement pattern specificity of resistance training on task performance
(Study Five). Thus, an extensive review of literature will not be presented here.
26
2.2.5 Type of pre-contraction
Many sporting tasks require concentric muscle action subsequent to eccentric
contraction of the muscle. Examples of such tasks include running, jumping,
throwing and bounding/hopping. It is clear that vertical jump height, for instance,
is increased when subjects are allowed an eccentric contraction
(countermovement) prior to the concentric phase of a jump (Häkkinen & Komi,
1985; Häkkinen et al., 1987; Voigt et al., 1995). Similar results have been shown
for upper body tasks such as the bench press (Wilson et al., 1991). Increases in
performance have been largely attributed to increases in the impulse produced
during the early (first 370 ms; Wilson et al., 1991) part of the concentric phase.
Therefore, muscle actions that are preceded by an eccentric contraction are
associated with improved dynamic performance.
This improved performance is mostly attributed to the stretch-shorten cycle (SSC)
phenomenon. It has been commonly suggested that when a load is placed on a
muscle, its elastic (compliant) elements are able to store energy after being
stretched; this energy is released when the muscle contracts concentrically. The
use of elastic energy during the concentric phase of a movement is believed to
augment power output and/or movement efficiency (Komi, 1984; Miller et al.,
1981; Norman & Komi, 1979). However, greater performances in tasks that are
preceded by an eccentric contraction may also be explained by the fact that the
muscles are more active after the eccentric phase. Bobbert et al. (1996) studied
the difference between vertical jumps with and without a countermovement (i.e. a
downward phase prior to the upward, propulsive phase) using modelling
techniques. Their results suggested that the countermovement allowed muscles
to achieve a ‘high level of active state’, attachment of cross-bridges, and force
before shortening. Muscles were therefore able to produce more force (perform
more work) earlier in the propulsive phase. Similar findings were also reported by
Walshe et al. (1997).
27
Motor unit recruitment may also vary when the pre-contractions used in training
exercises are changed. While smaller slow-twitch motor units are often activated
prior to larger fast-twitch motor units (Milner-Brown et al., 1973), Nardone et al.
(1989) demonstrated that a large proportion of high-threshold, fast-twitch motor
units were active during lengthening contractions. Therefore, fast-twitch motor
units that are not often activated during brief concentric contractions might be
better activated by a prior eccentric contraction.
Since movements utilising an eccentric component are functionally dissimilar to
those that do not, it may be important that training exercises for tasks that involve
prominent eccentric phases replicate the task pattern precisely. The influence of
type of pre-contraction will not be investigated in this thesis. It will however be
held constant between training groups in the training study that will investigate the
effect of movement pattern specificity of resistance training on task performance
(Study Three). Thus, a comprehensive review of literature will not be presented
here.
2.2.6 Summary
Adaptations to resistance training appear to be specific to the movement patterns
of the training exercises. It may be important therefore that training exercises
aiming to improve athletic performance be similar in their body position, laterality
and the joint angles through which the movement is performed. It would also be
important to replicate the contractions and pre-contractions. Most research
suggests that movement pattern adaptations are largely of neural origin.
However, some evidence suggests that adaptations at the sarcomere level may
be a factor. Research has not provided evidence in favour of any one
explanation.
28
2.3 EFFECT OF RESISTANCE TRAINING MOVEMENT VELOCITY ON
TASK PERFORMANCE
Physiological adaptations to training have been shown to be specific to the
velocity of training. Much of the research that has examined the velocity-specific
training effect have used isokinetic training and testing procedures with relatively
little research using free-weight, isotonic resistance training techniques. Since
adaptations to these two training modes may not be similar, the literature
reviewed in this section will be addressed with respect to training mode.
2.3.1 Isokinetic, velocity-specific training studies
While peak torque is often measured in isokinetic studies, the testing protocol
used by researchers such as Perrine and Edgerton (1978) and Caiozzo et al.
(1981) involved graded knee extensions. This was to ensure maximum force
production (torque maximum) occurred at a specific angle (30o of knee flexion) to
control oscillations in the dynamometer and limit fatigue during the initial stages of
the contraction. Small performance differences between ‘peak torque’ and ‘angle-
specific torque’ methods are possibly due to differences in testing protocol or
strength levels of athletes (Hortobágyi & Katch, 1990). However, comparisons
between ‘angle-specific’ and ‘peak torque’ methods are presented in Bell and
Wenger (1992) and Kannus et al. (1991) and show minimal differences between
the torque curves determined both ways. Therefore, for the purpose of this
review, the results from studies which have used ‘angle-specific’ and ‘peak torque’
methods will be considered together.
Velocity-specific training adaptations have been shown in numerous studies.
Moffroid and Whipple (1970) trained subjects on a knee extension exercise at
either 36o.s-1 or 108o.s-1 and tested at a range of velocities from 18 to 108o.s-1. All
subjects primarily increased torque at and below the training velocity with subjects
who trained at 108o.s-1 increasing their torque production at a greater range of
29
movement speeds. Similar results have been reported by a number of other
researchers (Costill et al. 1979; Coyle et al., 1981; Ewing et al., 1990; Lesmes,
1978; Petersen et al., 1989). Some studies have also shown torque and power
increases at slower speeds but also higher speeds after slow isokinetic training
(Caiozzo et al., 1981; Colliander & Tesch, 1990; Kanehisa & Miyashita, 1983;
Petersen, 1988). Thus, while there is substantial evidence suggesting that
strength, as measured by joint torque or power, increases most at the velocity at
which the subjects trained there may be some carryover to other velocities.
Interestingly, while few studies have shown an effect of periodised training,
Doherty and Campagna (1993) showed that periodised slow to fast velocity
training culminated in greater mean isokinetic torque at 180o.s-1 than a ‘slow’
training group and a ‘fast’ group who trained at that speed. Thus adaptations to
periodised training may be different to those of non-periodised training.
Despite the number of studies that report a significant velocity-specific training
effect after isokinetic training, some studies show contrasting results (Bell &
Wenger, 1992; Bell et al., 1989; Housh & Housh, 1993; Jenkins et al., 1984;
Lacerte et al., 1992). For example, Bell et al. (1989) showed that increases in
peak knee extensor torque were lowest at slow speeds and greatest at higher
speeds despite training being performed at an intermediate speed. Also, Housh
and Housh (1993) reported elbow and knee flexion/extension torque increases at
fast and slow speeds after training at intermediate speeds (120o.s-1). It has been
suggested therefore that training performed at intermediate velocities (100o.s-1 –
200o.s-1) may be associated with less-specific adaptation (Bell & Wenger, 1992)
although some researchers have reported velocity-specific adaptations even at
these velocities (Petersen et al., 1984). Therefore, despite some inconsistency,
the weight of evidence supports a velocity-specific adaptation to isokinetic
exercise. It is not clear why differential results have appeared, the unreliability of
isokinetic tests (Steiner et al., 1993), training status of subjects and the length of
training studies might be a factor.
30
2.3.2 Isokinetic training effects on task performance
Few researchers have investigated the transfer of strength gains made with
isokinetic training to performance improvements in isotonic/isoinertial tasks.
Smith and Melton (1981) showed that subjects who trained their knee extensors
and flexors at fast (180, 240 and 300o.s-1) speeds improved their vertical jump
(5%), broad jump (9%) and 40-yard sprint time (10%). Subjects who trained at
slow (30, 60 and 90o.s-1) speeds improved their vertical jump (4%), but did not
improve broad jump (0%) or 40-yard sprint time (-1%). This result suggests some
velocity-specific transfer occurs from isokinetic training to task performance.
However, Van Oteghen (1973) used a leg press exercise at two different velocities
to train volleyball players. After training, there was no difference in performance
of a jump test between the two groups although these groups performed better
than an untrained control group. Given that Smith and Melton (1981) found no
significant effect of training velocity on vertical jump also, it appears as though the
vertical jump is less affected by training velocity than broad jump and running
tasks. It is also unclear whether the lack of movement pattern similarity between
the tasks would have affected adaptations. Thus, while it is not conclusively
shown, it is possible that even high-velocity isokinetic training might improve
performance of complex high-speed tasks.
2.3.3 Free-weight, isotonic training studies
Research investigating the velocity-specific adaptations to free-weight, isotonic
training is also sparse. Increases in fast-speed dynamic performance has been
shown to be greater with high-speed (30% of 1RM) training and plyometric
training than slower resistance training (Wilson et al., 1993). There also seems to
be no effect of resistance training on the speed of an unloaded, complex
movement unless some training of the movement is performed (Voigt & Klausen,
1990). A similar result was found by Adams et al. (1992) who reported greater
(10.7 cm) improvements in vertical jump performance after combined squat and
31
plyometric training than squat (3.3 cm) or plyometric training (3.8 cm) alone.
Other studies failed to show a significant velocity-specific training effect with
resistance-type training. Palmieri (1987) found no significant differences in leg
power in a vertical jump between groups who performed squat lift training at slow,
fast, or periodised slow to fast movement speeds. Also, Young and Bilby (1993)
found no differences in strength or muscle size of subjects who performed either
slow or fast squat lifts despite a trend toward a greater rate of force development
in subjects who performed faster movements. Nonetheless, increases in strength
and power might occur easily regardless of training type in subjects with a limited
training history such as those in these two studies. Also, Pousson et al. (1999)
showed no changes in elbow flexor movement velocity of a group who performed
light-load (35% of 1 RM) training at their fastest possible speed. The difference in
training (isotonic) and testing (isokinetic/isometric) modes might explain the lack of
performance change (Duncan et al., 1989).
Unfortunately, studies that have investigated adaptations to high-velocity training
have used exercises performed at limb velocities below those achieved in many
sporting situations. For instance, the angular velocity at the hip during maximum
velocity running exceeds 500o.s-1 (Mann & Herman, 1985). It may be difficult to
consistently replicate, in a laboratory or gymnasium, speeds that are achieved in
the sporting situation; it is also unclear whether it is necessary to achieve these
speeds for beneficial adaptations to occur. Furthermore, isoinertial movements
are often characterised by a prolonged deceleration period toward the end of
concentric and eccentric phases. Such training is characterised by lower
movement velocities, lower muscle power and a reduced EMG of agonist muscles
compared to movements without a deceleration phase (e.g. bench throws;
Newton et al., 1997). Using this form of training may therefore not provide an
optimum training stimulus. Another factor that limits the use of data collected in
these studies is the length of training periods. Training studies are generally less
than three months in duration (e.g. Young & Bilby, 1993: 6 weeks). Therefore, the
effect of long-term high-velocity resistance training is still not clear. To understand
the influence of training velocity on task performance, the physiological
32
adaptations to resistance exercise must be considered.
2.3.4 Mechanisms contributing to velocity-specific strength changes
2.3.4.1 Neural Factors
Muscle Activation
Even during maximal voluntary contractions, individuals may not be able to fully
activate their muscles (Enoka & Fuglevand, 1993) or may not be able to fully
activate their muscles on each of a series of maximal contractions (Allen et al.,
1995). Much research has shown increases in surface EMG after both ‘traditional’
(Higbie et al., 1996; Narici et al., 1989; Ozmun et al., 1994) and explosive jump
training (Häkkinen & Komi, 1983, 1985, 1986; Häkkinen et al., 1985a,b) and
Häkkinen et al. (1987) showed increases in EMG accompanied increases in
power production of elite weightlifters during periods of higher-than-normal
training intensity. The increases in EMG were considered a strong indication of
increases in the level of total muscle activation. Other researchers however have
not shown increases in EMG after periods of resistance training (Cannon &
Cafarelli, 1987; Garfinkel & Cafarelli, 1992; Komi & Buskirk, 1972) or that only
‘explosive-type’ training has the propensity to increase muscle activation. Thus
there is some speculation that adaptations can occur without increases in EMG. It
is also possible that increases in EMG reflect increases in motor unit
synchronisation which is associated with higher EMG (Yao et al., 2000). It is
unclear whether there is a velocity-specific change in EMG after training.
The twitch interpolation technique first performed by Merton (1954) has been used
to examine levels of muscle activation. Most research has shown no change in
muscle activation after various forms of training using this technique (Brown et al.,
1990; Carolan & Cafarelli, 1992; Harridge et al., 1999; Herbert et al., 1998; Sale et
33
al., 1992). Supramaximal stimulation techniques have also shown no change
in stimulated force even after increases in voluntary force were seen (Davies &
Young, 1983; Davies et al., 1985; McDonagh et al., 1983; Young et al., 1985).
These results are possibly a result of muscle activation being nearly maximal in
most subjects (Carolan & Cafarelli, 1992; Garfinkel & Cafarelli, 1992). However
recent advances in the technique have shown that activation may often be
incomplete (Jakobi & Cafarelli, 1998; Kalmar & Cafarelli, 1999). A second reason
might be that the testing (isometric) and training (dynamic) modes were dissimilar
(Murphy & Wilson, 1996). It is therefore unclear whether voluntary muscle
activation assessed by muscle stimulation techniques is improved with training.
The measurement of transverse relaxation time (T2) of muscle by magnetic
resonance imaging has reportedly provided more accurate estimates of total
muscle activation (Fisher et al., 1990; Fleckenstein et al., 1993). Such research
has shown that, with few exceptions (e.g. Dowling & Cardone, 1994), maximal
muscle activation is uncommon (Adams et al., 1993; Allen et al., 1995). Akima
and colleagues (1999) also showed increases in muscle activation after just two
weeks of isokinetic training with no changes in muscle cross-sectional area or
fibre areas. However no research has compared changes in muscle activation in
subjects who have performed high- and low-velocity training.
While techniques that estimate muscle activation have a lot to offer in terms of our
understanding of neural adaptations to training, the results of such studies have
been inconclusive. Therefore other methods of assessing changes in the nervous
system have been employed. Evidence from such research has suggested that
increases in centrally-mediated muscle activation might not occur with resistance
exercise. Lyle and Rutherford (1998) reported similar increases in voluntary
strength of subjects trained by tetanic stimulation (involuntary) or under voluntary
conditions. Martin et al. (1994) has also shown increases in strength with training
involving electrical stimulation of relaxed muscle. Since neural commands are not
required for the muscular contraction in stimulated contractions it is unlikely that a
central adaptation could occur. Herbert et al. (1998) also showed that while
34
strength increased in weight training subjects, others who performed imagined
contractions did not improve. There were also no changes in muscle recruitment
as measured by twitch interpolation. Thus, rapid and significant increases in
strength have been shown after training where central nervous system changes
are unlikely. There is mounting evidence that increased muscle recruitment
mediated by the CNS does not occur with resistance training or is at least not the
only contributing factor to strength improvements.
‘Muscle activation’ describes both the number of active motor units and their
discharge rates (firing frequency). Evidence from research investigating
maximum discharge rates of motor units suggests motor units rarely receive
action potentials at a rate required for maximum activation to occur (Bellemare et
al., 1983; De Luca et al., 1982; Freund et al., 1975; Tanji & Kato, 1973).
However, those motor units with high-thresholds for recruitment (typically fast-
twitch) decline in their discharge rates rapidly after the motor unit becomes active
(De Luca et al., 1982; Grimby & Hannerz, 1977; Marsden et al., 1983). Thus it is
possible that motor units with high discharge rates are difficult to record and might
produce biased (lower) estimates of discharge rate (Enoka, 1997). Nonetheless,
high discharge rates among motor units occur infrequently. Increases in
discharge rates would thus be useful in allowing greater muscle forces to be
produced.
The trainability of motor unit discharge rate has not been conclusively determined.
Disuse of a muscle has been shown to reduce a subject’s ability to activate that
muscle (Duchateau & Hainaut, 1990; Yue et al., 1994). For example, Duchateau
& Hainaut (1990) immobilised subjects’ hands and wrists for 6-8 weeks.
Maximum recruitment thresholds for the muscles studied increased from
approximately 30% to 50% of MVC suggesting that motor units were not as
readily recruited. Few studies have investigated the effects of resistance training
on discharge rates. Patten et al. (1995) found an increase in the maximum
discharge rates for elderly subjects (36 to 46 Hz) but not for young subjects (47 to
46 Hz) in hand muscles. Leong et al. (1995) also showed that elderly subjects
35
could possibly increase their motor unit discharge rates by comparing
weightlifters and inactive subjects (mean age = 71 yrs). While there were no
differences in discharge rates during submaximal knee extensions discharge rates
were significantly higher for the weightlifters during maximal efforts (25 vs 20 Hz).
Thus, at least in elderly subjects, resistance training appears to cause an increase
in the discharge rates of motor units during maximal efforts. Again, it is unclear
whether such adaptations occur with high-velocity training although such an
adaptation could have benefits for high-speed force production.
Selective Activation of Muscles
Muscles that have the same or similar actions are often activated differently
depending on the constraints of a task (Buchanan & Lloyd, 1997; Nakazawa et al.,
1993; Nardone & Schieppati, 1988; Van Gröeningen & Erkelens, 1994). Studies
investigating muscle recruitment patterns during movements of different speeds
have shown that muscles with high fast-twitch fibre content are recruited mostly
when high forces or movement velocities are required (Duchateau et al., 1986;
Nardone & Schieppati, 1988). The selective recruitment of muscles with high fast-
twitch fibre contents might be an advantage in movements where shortening
velocities are fast. In extreme cases the recruitment of slower-contracting
muscles might retard muscle contraction. It is also likely that selective recruitment
of fast-contracting muscles would be particularly important in tasks involving rapid
alternating (concentric-eccentric) movements. Indeed the performance of
eccentric contractions, especially fast contractions, largely incorporates fast-twitch
fibres and muscles with high fast-twitch fibre content (Nardone & Schieppati,
1988). Evidence that such a phenomenon might be present has also been
presented by Moritani and coworkers (1990) who reported electromyographic
evidence of selective fatigue of the medial gastrocnemius as compared to the
soleus during prolonged (60 s) hopping. Whether high-speed training affects the
recruitment of muscles has yet to be determined.
36
Muscle activation strategies might not be wholly related to the muscles’
contraction properties. Almasbakk and Hoff (1996) found that groups who trained
with light or heavy bench press loads improved their movement velocities similarly
in bench press tests. The authors hypothesised that since the group who trained
with almost no load improved their performance similarly to a heavy training
group, velocity-specific adaptations were primarily a result of ‘learning’ or more
efficient inter-muscular coordination. However testing loads were also very light
(� 20 kg). It is also unclear if these training groups would have improved as much
as a group who trained at high velocities. Pousson et al. (1999) found that
subjects who performed fast contractions against a light load (35% 1 RM) had less
co-contraction between agonist (biceps brachii) and antagonist (triceps brachii)
muscle groups, although only at the highest (300o.s-1) test velocity. While such
changes were not consistent across speeds, the result suggests that some
change in agonist/antagonist co-activation might mediate velocity-specific torque
changes.
Selective Activation of Motor Units
Fast-twitch motor units contain fibres that have faster contraction and half-
relaxation times. It would therefore be advantageous to recruit these motor units
preferentially in, or at least at onset of, high-speed muscular contractions. Motor
units are most often recruited in accordance with the size principle of recruitment
(Desmedt, 1981; Henneman et al., 1964) which suggests that motor units are
recruited in order from those with small axon diameters to those with large
diameters (i.e. from slow- to fast-twitch). Such recruitment strategies have been
shown under isometric ramp (Milner-Brown et al., 1973), dynamic (Kato et al.,
1985) and ballistic (Desmedt & Godaux, 1977) conditions. Nonetheless, research
has shown early recruitment of fast-twitch fibres in fast isometric (Grimby &
Hannerz, 1968), twitch and rapid acceleration (Grimby & Hannerz, 1977) and
faster eccentric (Nardone et al., 1989) contractions. The central synaptic
mechanisms responsible for selective recruitment strategies is as yet unknown
(Burke, 1991; Nardone et al., 1989).
37
Motor Unit Synchronisation
Motor unit synchronisation refers to the coincident timing of impulses from motor
units (Milner-Brown et al., 1973). Milner-Brown et al. (1973) showed that
weightlifters exhibited greater synchronisation (measured by a surface EMG
technique) than control subjects. Furthermore, subjects who performed six weeks
of resistance training increased their synchrony. Thus motor unit synchronisation
has been regarded as an adaptation to resistance-type exercise. Semmler and
Nordstrom (1998) echoed such findings and Moritani et al. (1987) reported
increased synchronisation of biceps brachii motor units after just two weeks of
high-velocity strength training. Nonetheless, evoked stimulation studies have
shown that greater forces (Clamann & Schelhorn, 1988; Lind & Petrofsky, 1978;
Rack & Westbury, 1969) and smoother contractions (Clamann & Schelhorn, 1988)
were possible with asynchronous stimulation. Asychronous stimulation might be
beneficial in that the first motor units to become active could overcome the
slackness of series elastic components of nearby fibres and allow the shortening
of those fibres to more directly result in muscle shortening.
Also, the rate of force development is greater in voluntary than evoked
contractions; evoked contractions are characterised by greater motor unit
synchrony (Miller et al., 1981). Thus it has been suggested that asynchronous
motor unit recruitment might be advantageous for increasing the rate of force
development (Behm & Sale, 1993b). At least, greater synchrony seems not to be
associated with greater force development.
Nonetheless, Miller’s research (1981) also showed that agonist muscles exhibited
a pre-movement silence (a brief period of minimal activity of alpha motoneurons)
that could allow more motoneurons to come to a non-refractory state. Such a
response has been hypothesised to allow greater motor unit synchronisation
(Conrad et al., 1983; Moritani & Shibata, 1994). While pre-movement silence is
not consistently exhibited prior to maximal concentric contractions in all subjects,
greater pre-movement silence has been shown to be more consistent in elite
38
power athletes (Kawahats, 1983). Nonetheless, pre-movement silence has
also been suggested to improve stretch-shorten cycle use (Aoki et al., 1989;
Walter, 1988) and be a built-in command by the central movement generators to
allow a switch between contraction sequence programs. Thus silent periods are
not necessarily evidence of central adaptations to increase motor unit synchrony.
Recent research (Yue et al., 1995) however has shown limitations with the surface
EMG method for assessing motor unit synchronisation. Newer cross-correlogram
procedures however also show that motor unit synchronisation may be variable.
Certainly synchronisation is influenced by handedness (Schmied et al., 1994;
Semmler & Nordstrom, 1998) and learning (Schmied et al., 1993). Either way,
changes in motor unit synchronisation hint that changes in neural connectivity can
occur (Kirkwood & Seers, 1991). Future research needs to compare differences
in motor unit synchronisation after high- and low-velocity resistance training in
order to describe the effects of movement velocity on motor unit synchronisation.
2.3.4.2 Muscular Factors
Muscle architecture
Muscle architecture refers to the size of a muscle and to the length and angulation
(pennation) of its fibres. In addition to changes in muscle (or fibre) hypertrophy,
changes in fibre length and pennation can occur with training. Longer fibres have
been theoretically and experimentally shown to exhibit faster contraction velocities
(Burkholder et al., 1994; Sacks & Roy, 1982; Wickiewicz et al., 1984). Indeed
longer fibres have been found in well-trained sprinters than in long distance
runners (Abe et al., 1999) and lesser-trained sprinters (Kumagai et al., 2000).
Also, Van Eijden et al. (1997) found that jaw muscles that are predominant in jaw
closing where high forces are required possess shorter fibres than muscles for jaw
opening where lower forces are required. Animal studies have shown that
increases in fibre length occur by an increase in the number, but decrease in the
39
length, of sarcomeres within the fibre while the opposite is true for decreases in
fibre length (Goldspink et al., 1974; Heslinga et al., 1995; Tabary et al., 1972).
Moreover, these changes can take place within hours or days of a stimulus
(Williams et al., 1986; Williams, 1990). Stimuli in research studies has included
immobilisation in a shortened (Goldspink et al., 1974; Heslinga et al., 1995;
Tabary et al., 1972) or lengthened position (Goldspink et al., 1974; Heslinga et al.,
1995; Williams et al., 1986) and electrical stimulation (Williams et al., 1986). Thus
it appears that physical stimuli can induce changes in fibre length. Differences in
fibre length between athletic populations may therefore be a specific adaptation to
the work performed by the athletes.
Muscles that frequently contribute to movements requiring high force also often
have greater pennation than muscles that contribute to higher-velocity, low force
movements (Van Eijden et al., 1997). It is unclear how pennation changes with
training. Some researchers have shown increases in pennation after resistance
training (Blazevich & Giorgi, 2001; Blazevich et al., 1998; Kawakami et al., 1995)
while others have shown no change (Rutherford & Jones, 1992). It is also unclear
how increased pennation benefits high force development. Some researchers
suggest that greater pennation allows more contractile tissue to attach to a given
area of tendon (Kawakami et al., 1993; Rutherford & Jones, 1992). However,
while some studies support a relationship between muscle pennation and size
(Kawakami et al., 1993, 1995; Rutherford & Jones, 1992 [cross-sectional
analysis]) others do not (Blazevich et al., 1998; Henriksson-Larsén et al., 1992;
Rutherford & Jones, 1992 [longitudinal study]). The lack of pennation changes
with hypertrophy might be due to increases in the packing density of contractile
proteins which has been shown after resistance training (Claassen et al., 1989;
Horber et al., 1985; Jones & Rutherford, 1987), although the extent to which
packing density occurs is debated (Claassen et al., 1989). It is also possible that
pennation produces a ‘gearing’ effect rather than simply being a response to
muscle hypertrophy. Fibres of pennate muscles shorten less for a given tendon
excursion which would allow sarcomeres to work closer to their optimum length
during high-force contractions.
40
Given muscles that frequently perform high-force, low-velocity contractions tend to
have greater pennation and shorter fibres while the opposite is true for muscles
that perform low-force, high-velocity contractions, architectural adaptations could
occur with velocity-specific training. Architectural changes occur rapidly and could
therefore partly explain early adaptations to such training.
Muscle hypertrophy
The number of parallel sarcomeres in the muscle (Roy & Edgerton, 1991) largely
determines the force generated by a fully activated muscle. Either adding more
sarcomeres within muscle fibres or adding more fibres could increase the number
of parallel sarcomeres. Although increases in fibre number (hyperplasia) have
been shown in animal muscles (Gonyea et al., 1986; Tamaki et al., 1992) it is not
possible to directly determine whether the process occurs in humans.
Nonetheless, muscle size increases in resistance-trained subjects has been
associated with both fast-twitch and slow-twitch fibre hypertrophy (Alway et al.,
1992; Bell & Jacobs, 1990; Hortobágyi et al., 2000; MacDougall et al., 1984; Volek
et al., 1999). It has been suggested that the time course of hypertrophy is related
to the fibre type (Abernethy et al., 1994). Indeed, hypertrophy of fast-twitch fibres
may occur earlier in a strength training program (< 8 weeks) than hypertrophy of
slow-twitch fibres (Häkkinen et al., 1981).
Explosive-type training might cause preferential hypertrophy of fast-twitch fibres
(Esbjörnsson Liljedahl et al., 1996; Mero et al., 1983). Tesch et al. (1987) showed
increases only in type II fibres after heavy resistance and plyometric training.
Esbjörnsson Liljedahl et al. (1996) and Linossier et al. (1997) reported increases
in type IIb fibre area with increased power in a cycle sprint after sprint training.
Furthermore, changes have been shown, at least after short periods of training (4
weeks), to be greater in previously non-resistance trained women than men
(Esbjörnsson Liljedahl et al., 1996). Such findings have been attributed to women
having smaller fast-twitch fibre areas prior to training (Esbjörnsson Liljedahl et al.,
41
1996; Wang et al., 1993). In women, type I fibre areas are generally greater
than IIa and IIb while in men type IIa fibre areas are greater than IIb and I (in that
order [Simoneau et al., 1985; Staron et al., 1984; Staron et al., 1990]). Selective
hypertrophy of fast-twitch fibres might contribute to the velocity-specific
adaptations reported in the literature. Muscle protein synthesis is significantly
elevated within four hours of training (Chesley et al., 1992; MacDougall et al.,
1992, 1995) and increases in hypertrophy have been seen after training for as
little as four weeks (Esbjörnsson Liljedahl et al., 1996). Thus, selective
hypertrophy of fast-twitch fibres could be a factor in early velocity-specific
performance improvements.
Fibre-type transformation (MHC expression)
Eighty-five percent of the myosin molecule is composed of myosin heavy chains
(MHC; Whalen, 1985). The bending of the myosin molecule that pulls actin and
results in sarcomere shortening is performed by a combination of elastic distortion
and active rotation in the heavy chain. This occurs between the light chain (at the
head of the myosin molecule) and the catalytic domains of the myosin molecule
(Irving et al., 2000). Thus the maximum shortening speed of a muscle is possibly
affected by the expression of different MHC isoforms. These isoforms are shown
in Table 2.1. The type of MHC present in muscle is suggested to be a major
determinant of skeletal muscle function (Bottinelli et al., 1991; 1992; Green, 1992).
Muscle fibres that are predominant in the MHC I isoform exhibit slower shortening
velocities (Harridge et al., 1996; Larsson & Moss, 1993) and lower power outputs
(Bottinelli et al., 1996) than fibres predominant in the MHC II isoforms. Training
may alter this MHC expression. Tesch et al. (1989) showed that Olympic and
power lifters possessed a greater fast-twitch to slow-twitch fibre ratio than
bodybuilders. Saltin and Golnick (1983) also reported that successful power
athletes had a higher percentage of fast-twitch fibres in propulsive muscles. Such
differences suggest that either genetics or training influenced their fibre types.
42
Table 2.1. Myosin Heavy Chain isoforms in human skeletal muscle. There are also various
intermediaries, and other isoforms shown only in muscle from non-human animals.
Slow-twitch muscle Fast-twitch muscle
I IIa
Ic IIx or IId
IIb
IIeo, IIsf
Note: IIx/IId are the same myosin type thought to be a hybrid of IIa and IIb, IIeo refers to a type
found in extraocular muscle of humans, IIsf refers to a type found in the human jaw.
MHC changes have indeed been shown related to the training stimulus with
endurance-type exercise and some strength training regimes producing greater
type I MHC content (Adams et al., 1993; for reviews see Abernethy et al., 1994;
Jürimäe, 1997). While such changes may be related to the metabolic effects of
training, Pette and Vrbovà (1992) showed that low-frequency stimulation
transformed faster MHC types to slower types. Also, high-frequency stimulation
has been suggested to change slow-twitch fibres of the soleus muscle to fast-
twitch fibres (Ausoni et al., 1990; Gorza et al., 1988). These results suggest that a
mechanical stimulus, and the frequency of a muscle’s activation under the
stimulus (high/low frequency), might affect MHC expression.
Despite changes in MHC content after resistance training, these changes have
not been closely related to changes in maximal slow-speed strength (Jürimäe et
al., 1996; Carroll et al., 1998). Myosin heavy chain shift might be most closely
related to the velocity of training movements. Indeed Mannion et al. (1995)
showed that type II fibres increased in proportion with dynamic, high-intensity
exercise capacity. Other research has also showed decreases in type I and
increases in type II MHC isoforms after sprint cycle training (Jansson et al., 1990)
and combined sprint and resistance training (Andersen et al., 1994).
Nonetheless, Harridge et al. (1998) found no changes in MHC isoform expression
after six weeks of cycle sprint training. Training involved three-second sprint
intervals designed not to induce metabolic fatigue. The result suggests perhaps
that the mechanical stimulus was too low for changes to occur or that both
metabolic and mechanical factors contribute to MHC isoform expression.
43
Alterations in fibre-type have been seen after only two weeks of training in
humans (Staron et al., 1994), and after as little as four (Goldspink et al., 1991)
and ten (Ohira et al., 2000) days in animals. It is therefore possible that specific
myosin isoform changes could at least partially account for rapid improvements in
high-velocity force production.
Contractile Kinetics
The contractile apparatus consists of myosin, actin, tropomyosin, troponin C,
troponin I and troponin T (Gunning & Hardeman, 1991; Tsika et al., 1987).
Further, the myosin molecule is composed of two heavy chains (~200 000 Da
[daltons]) and four light chains ~20 000 Da). There are two different forms of light
chains, the phosphorylatable or regulatory (MLC2) and the alkali (MLC1 and
MLC3) light chain each with varying isoforms. It is on MLC 2 that the myosin
ATPase-mediated phosphorylation occurs that allows actin-myosin sliding. The
predominant isoform present in muscle is strongly related to its twitch force and
velocity (Jostarndt-Fogan et al., 1998; O’Brien et al., 1992). These isoforms are
summarised in Table 2.2.
Table 2.2. Contractile protein isoforms (not including MHC) in human skeletal muscle.
Protein Slow-twitch muscle Fast-twitch muscle
Regulatory light chain 2S, 2S’ 2F
Alkali light chain 1Sa, 1Sb 1F,3F
Actin ásk ásk
Tropomyosin â, áS â, áF
Troponin C S F
Troponin I S F
Troponin T S F
S = slow, F = fast.
The proportions of light chain (LC) myosin isoforms has been shown to change in
animal muscle. Cross-innervation of rabbit soleus resulted in increased fast LC
isoforms and decreased slow isoforms in both treated and contralateral limbs
44
(Srihari et al., 1981). Also, suspension of rats by their tails was associated with
increases in fast LC isoforms in the soleus, whereas 30 s sprint or endurance
training lead to a predominance of slow isoforms in the vastus lateralis
superficialis (Guezennec et al., 1990). Few studies have reported no changes in
LC isoforms after training (e.g. Bar et al., 1989).
While some research has shown that force development (and Ca2+ sensitivity) is
related to a muscle’s troponin isoforms (Geiger et al., 1999), it is likely that LC
isoforms are the greatest determinant. Lowey and colleagues (1993) showed that
the removal of the LC from myosin reduced actin sliding velocity from 8.8 to 0.8
microns.s-1 while there was no significant change in myosin ATPase activity.
Reconstitution of either the regulatory or alkali light chain caused moderate
increases in actin velocity while reconstitution of both LC’s restored original sliding
velocity. Thus the sliding velocity of actin was not related to myosin ATPase
activity but to the presence of light chains.
Moreover, the rate of phosphorylation of the regulatory LC is significantly related
to force and rate of force development in both isometric (Grange et al., 1995;
Sweeney & Stull, 1990) and dynamic (Grange et al., 1998) contractions. Fast-
twitch muscle has been shown to contain largely fast LC isoforms (Jostarndt-
Fogan et al., 1998). Indeed O’Brien et al. (1992) reported that proportions of slow
myosin heavy chain and LC isoforms in chronically-stimulated sheep latissimus
dorsi muscle were 86% and 92% respectively after 3 months. The slow form of
tropomyosin constituted only 64% and changes in troponin T were only significant
after 5 months of stimulation. Therefore changes in myosin heavy and light
chains preceded changes in tropomyosin and troponin.
Thus, the shortening velocity of a fibre is strongly related to the LC isoforms
present. Since the rate of phosphorylation of the LC influences the contractile
properties of a fibre, isoform changes have been seen in less than two weeks and
the presence of LC’s appears necessary for physiological speeds of sarcomere
45
shortening, changes in LC isoforms in muscle might largely explain velocity-
specific adaptations to training.
Muscle calcium kinetics
Calcium (Ca2+) release from and uptake to the sarcoplasmic reticulum influences
sarcomeric contraction force at submaximal contraction levels (Booth et al., 1997;
Ortenblad et al., 2000). Muscle fatigue that causes a decreased force output
(Booth et al., 1997; Tupling et al., 2000) or rate of force development (Ortenblad
et al., 2000) has been associated with reduced efflux of Ca2+ from, and re-uptake
to, the sarcoplasmic reticulum. Nonetheless, such changes have been shown not
to affect sarcomere relaxation time (Booth et al., 1997; Hunter et al., 1999). Also,
while increases in Ca2+ efflux are associated with higher contraction forces at
submaximal Ca2+ levels, it has not been shown that supra-physiological amounts
of Ca2+ improve contractile force above a sarcomere’s previous maximum.
Increases in Ca2+ release and repeated sprint performance have been shown with
sprint training (Duke & Steele, 2000). However the greater Ca2+ release might be
a response to other changes that have taken place in the sarcomere. For
example, greater phosphate availability induces Ca2+ release. Increased
phosphate results from increased myosin ATPase activity (which is higher in ‘fast’
fibres than ‘slow’ fibres). Indeed Geiger et al. (1999) showed that troponin
isoforms, which are related to the myosin heavy chain isoforms present in a
sarcomere, affect the Ca2+ sensitivity of the actin-myosin interaction. Thus
changes in Ca2+ availability after training might be related to the rate of cross-
bridge cycling (and therefore myosin ATPase activity) rather than being an
adaptation which in itself improves sarcomeric shortening speed.
Muscle-based Enzymes
Muscle-based enzymes act as catalysts for chemical reactions in muscle cells.
46
Increases in enzymes that speed reactions associated directly with muscle
contraction could therefore be considered beneficial to high-speed performance.
Some studies have reported increases in glycolytic enzymes after periods of
sprint-type training (Cadefau et a., 1990; Costill et al., 1979; Jacobs et al., 1987;
Roberts et al., 1982) while relatively few have not have not (Henriksson &
Reitman, 1976; Hickson et al., 1976). Nonetheless, enzymes whose activities
have been shown higher after sprint-type training include hexokinase,
phosphofructokinase, lactate dehydrogenase and creatine kinase (Dawson et al.,
1998; Hellsten et al., 1996; MacDougall et al., 1998). Greater activity of these
enzymes is not likely to result in increases in the contractile speed of a muscle,
but would result in increases in energy produced through glycolytic pathways and
allow a greater quantity of work to be performed in a short duration activity.
Myosin ATPase splits ATP to ADP and an inorganic phosphate prior to cross-
bridge interaction to provide energy for the conformational change in the myosin
molecule that pulls actin and results in sarcomere shortening. A muscle’s
contraction speed is significantly related to its fibre’s myosin ATPase activity
(Enoka, 1994; Báráry, 1967). Indeed ‘fast-twitch’ fibres are characterised by their
high quantity of myosin ATPase (Essén et al., 1975). Increases in myosin
ATPase activity have been reported in sprint-type training studies where training
bouts are brief (< 10 s; Dawson et al., 1998; Thorstensson et al., 1975)
suggesting that training can affect the enzyme’s activity. No changes were seen
after 12 weeks of high-intensity resistance training (Green et al., 1998).
Since both the size and number of type II fibres increase with high-velocity
training, the increase in total muscular myosin ATPase activity could be quite
large. Thus, while glycolytic enzyme activities are unlikely to affect absolute
muscle contraction speed, increases in myosin ATPase activity after training have
been thought a major contributor to the shortening velocity of sarcomeres.
Nonetheless, Lowey et al. (1993) showed that the removal of the light chains
(which are located on the myosin head) from the myosin molecule is associated
with dramatic decreases in sarcomere shortening velocity with no significant effect
47
on myosin ATPase activity. Thus there is at least some evidence that myosin
ATPase, while correlated with sarcomere shortening velocity, is not responsible
for regulating the shortening velocity of the sarcomere.
2.3.5 Summary
With respect to velocity specificity, results of studies investigating responses to
isokinetic training suggest that strength increases are greater at, and perhaps
slightly below, the movement velocities of the training exercises. When an
isotonic (isoinertial) training mode is used, subjects who perform movements at
higher velocities tend to perform better in tasks requiring higher movement speeds
(Wilson et al., 1993). It appears therefore that resistance training at movement
speeds approaching those of a sporting task are more likely to lead to task
improvement than resistance training at slow movement speeds. The
mechanisms responsible for velocity-specific performance changes are complex
and not well defined. It appears as though muscular factors such as architectural
changes (pennation and fibre length), fast-twitch fibre hypertrophy and transition
from slow light and heavy chain myosin isoforms to fast isoforms could explain
many of the early changes. The contribution of neural factors is less clear. While
some research suggests that increased motor unit recruitment and/or selective
activation of fast motor units might improve high-velocity force output as much
evidence questions their influence. Clearly more research is required with respect
to the time-courses of both neural and muscular changes before a complete
model of velocity-specific adaptations is possible.
48
2.4 BENEFITS OF RESISTANCE TRAINING TO HIGH-SPEED TASK
PERFORMANCE
2.4.1 Strength and mass of muscle and connective tissue
An increase in muscle mass is commonly observed with traditional forms of
resistance training (Alway et al., 1992; Bell et al., 1990; Kawakami et al., 1995;
Tracey et al., 1999). Given that the force generated by a muscle at maximum
stimulation is largely determined by the number of half sarcomeres arranged
parallel in a muscle (Roy & Edgerton, 1991), muscular hypertrophy could be
considered beneficial to power production during high-speed movements.
Furthermore, muscular hypertrophy often occurs with increases in the amount of
connective tissue within the muscle (Enoka, 1988; Kuno et al., 1990; Wang et al.,
1993). Force can be transmitted laterally in muscle (Huijing, 1999; Monti et al.,
1999; Street, 1983) so it has been suggested that the increase in connective
tissue might also improve strength (Jones et al., 1989). There might be a second
benefit to the increase in connective tissue with training however. Large forces
are imposed on tendons, muscles and ligaments (Behm, 1991) during high-speed
movements. Since strength training increases the strength and mass of
connective tissue, it may also enable the body to cope with the large forces of
high speed/explosive strength training (Miffed, 1988; O’Bryant et al., 1988). This
adaptation may benefit both injury prevention and the utilisation of stored elastic
energy in stretch-shorten cycle activities.
Increases in muscle activation have also been reported after resistance training
(Akima et al., 1999; Häkkinen & Komi, 1983, 1986; Ozmun et al., 1994). The
increase in activation is often attributed to either a greater number of active motor
units and/or an increase in their firing rate. However, much evidence for
increased activation has come from studies employing surface EMG techniques
(Häkkinen & Komi, 1983; 1986; Moritani & DeVries, 1979; Ozmun et al., 1994).
Many other researchers have shown no increases in EMG after resistance training
49
(Cannon & Cafarelli, 1987; Garfinkel & Cafarelli, 1992; Herbert et al., 1998;
Narici et al., 1996; Rich & Cafarelli, 2000) and some increases in EMG could
perhaps be a result of greater muscle synchronisation (Yao et al., 2000). Total
muscle recruitment using twitch interpolation (Brown et al., 1990; Carolan &
Cafarelli., 1992; Harridge et al., 1999; Herbert et al., 1998; Sale et al., 1992) and
tetanic stimulation (Davies & Young, 1983; Davies et al., 1985; McDonagh et al.,
1983; Young et al., 1985) has shown no changes in muscle recruitment with
training. Only recently has evidence from magnetic resonance imaging methods
supported the long-held belief that greater muscle activation results from
resistance exercise (Akima et al., 1999). Furthermore, strength increases have
been shown after twitch (Martin et al., 1994) and tetanic (Lyle & Rutherford, 1998)
stimulation of muscles where increases in muscle activation mediated by the
central nervous system are unlikely to have occurred. Thus it is still not clear
whether the ability to recruit motor units during maximal contractions is enhanced
by resistance training.
Increases in muscle strength may shift the force-velocity curve upwards. Humans
are unlikely to produce greater high-velocity force outputs than low-velocity force
outputs (despite some evidence that sprint runners produce greater isokinetic
force at 180o.s-1 than at 30o.s-1 [Alexander, 1990; Blazevich, 1995]). Thus,
improving the low-velocity area of the force-velocity curve might allow more scope
for force increases at high-velocities. This has prompted some authors to suggest
that strength gains from lower-velocity resistance training would allow more scope
for speed/power development, in advance of high-velocity training (Poliquin,
1992).
Heightened co-contraction can be expected during the performance of high-speed
(Karst & Hasan, 1987; Lestienne, 1979; Marsden et al., 1983) or repetitive,
alternating tasks (Cooke & Brown, 1990). Heightened co-contraction would
increase the energy cost of a task. It would be beneficial if muscular co-
contraction can be reduced in high-speed movements by resistance training.
Decreases in muscular co-contraction have been reported after periods of
50
isometric (Carolan & Cafarelli, 1992) and dynamic (Häkkinen et al., 1998;
Pousson et al., 1999) resistance training. However, only Pousson et al. (1999) has
provided evidence for such an occurrence after high-velocity training. Thus, little
evidence exists to suggest that changes in muscular co-contraction occur after
such training.
2.4.2 Consequences of Resistance Training for High-speed Task
Performance
While, in theory, the physiological changes that result from resistance training at
different movement velocities may aid the development of high-speed strength, it
is unclear whether resistance training improves speed or power performance
above those gains made by practicing the task (eg running, cycling, throwing etc.)
alone. Concurrently using high-velocity resistance training and task practice might
improve performance in that task more than using concurrent low-velocity
resistance training and task practice during short (seven week) training periods
(Blazevich, 1995). However, little research (e.g. Hoff & Almasbakk, 1995; Voigt &
Klausen, 1990) has demonstrated that the use of resistance training improves
performance more than task practice alone. While decreases in muscular co-
contraction have been shown after resistance training (Häkkinen et al., 1998;
Pousson et al., 1999), low-velocity resistance training could possibly promote non-
beneficial changes in the nervous system. Barrata et al. (1988) showed that co-
contractions during a slow (15o.s-1) isokinetic leg extension exercise were
increased (four-fold) in athletes who performed leg flexor resistance training (as
part of their own physical training; N=10) as compared to two groups who did not
perform leg flexor training (athletes, N=7 and untrained, N=7). Given that neural
adaptations, in response to resistance training, may occur within weeks (Moritani
& DeVries, 1979; Sale, 1987), it is plausible that even a short duration resistance
training program may increase levels of co-contraction, and therefore decrease
the efficiency of a fast, repetitive movement such as sprint running or cycling.
Resistance training has also been shown to elicit different architectural changes to
51
those thought optimum for high speeds of muscular contraction. Muscles that
often perform high-force, low-velocity contractions tend to possess short fibres
with large pennation (Burkholder et al., 1994; Van Eijden et al., 1997). The
opposite is common in muscles that often perform low-force, high-velocity
contractions. Indeed faster sprint runners have been shown to have muscles with
longer fascicles (commonly used as an estimate of fibre length) than slower sprint
runners (Kumagai et al., 2000). Such a result supports research findings that
longer fibres contract faster than shorter fibres (Sacks & Roy, 1982; Wickiewicz et
al., 1984). Despite muscles with lesser pennation and longer fibres perhaps being
best for high-speed task performance, resistance training has been shown to
promote the opposite (Blazevich & Giorgi, 2001; Kawakami et al., 1993; 1995).
Thus architectural adaptations to slow-speed resistance training might not be
conducive to high-velocity force production.
Finally, adaptations to resistance training have been shown specific to the
movement velocity (Caiozzo et al., 1981; Colliander & Tesch, 1990; Kanehisa &
Miyashita, 1983; Petersen, 1988), body position (Solomonow et al., 1986; Wilson
et al., 1996), joint angles or muscle lengths (Kitai & Sale, 1989; Weir et al., 1994),
laterality (Howard & Enoka, 1991; Tanaguchi, 1997) and contraction type (Lacerte
et al., 1992; Tomberlin et al., 1991) of the training movement. Thus the ‘transfer’
of strength gained in one task to another is often limited. Regardless of whether
resistance training has benefits and consequences for high-speed task
performance, one could question the likely performance improvements that would
result from resistance training. Despite this, resistance training is still commonly
performed by speed/power athletes providing anecdotal evidence at least that this
form of training has some benefits.
2.4.3 Summary
While high-velocity training is required for high-velocity strength adaptation, low-
velocity strength training may benefit high-velocity force development. Increases
in muscle strength, connective tissue strength and perhaps motor unit recruitment
52
may directly influence high-velocity force production. Further, low-velocity,
high-force resistance training may increase training variation when performed with
high-speed training to promote continuous improvements and avoid a plateau
(which is more likely to occur with a less variable training program). Therefore,
periodised training, which utilises high-force resistance training prior to, and
interspersed with, high-velocity resistance training may be beneficial for
speed/power development. Unfortunately, adverse physiological changes such as
increases in muscular co-contraction, increases in muscle pennation and
decreases in fibre length may, at least partially, negate the benefits of low-
velocity, high-force resistance training. Learning to effectively combine low- and
high-velocity resistance training with task practice may be the necessary step in
determining the ‘ideal’ training program for speed/power development.
2.5 IMPLICATIONS OF THE LITERATURE REVIEW
Athletes often use resistance training in an attempt to improve high-speed force
production since increases in muscle and tendon strength, the recruitment of
muscle fibres and increases in muscle size can improve dynamic force production.
Studies investigating neuromuscular and performance adaptations to RT have
shown the effects of altering the movement patterns and velocities at which
training. Nonetheless, research has not shown whether the benefits of RT
outweigh the costs when such training is used in a concurrent regime. Foreseeing
the likely outcomes of concurrent training is also difficult since the neuromuscular
adaptations to training are not well understood. Particularly, assigning neural
explanations (as apposed to muscular explanations, or a combination of the two)
as the cause of performance changes has been problematic. Given the inherant
difficulty in mimicing many sporting movements it is important that athletes and
coaches are informed of the importance of movement-specific training over the
general strength programs often used concurrently with speed/power training. It
would be of value to determine, 1) whether resistance training augments
performance in high-speed activities more than task training alone, 2) whether the
resistance training is required to have the same movement pattern as the task
53
being trained for, 3) whether the resistance training should be performed at a
velocity approaching that of the task being trained for, and 4) what mechanisms
underlie adaptations to concurrent speed and resistance training. Further
research is required to answer these questions.
54
CCHHAAPPTTEERR 33:: SSTTUUDDYY OONNEE
55
A COMPARISON OF MOVEMENT PATTERNS
OF THE VERTICAL JUMP, BROAD JUMP AND
ACCELERATION PHASE OF THE SPRINT RUN
TO THE SQUAT LIFT AND FORWARD HACK
SQUAT EXERCISES.
3.1 INTRODUCTION
Tasks such as the vertical jump, standing broad jump and sprint run are
commonly performed in many sports, as well as in studies investigating
human performance. Given that adaptations to resistance training are
specific to the movement patterns of the training exercises used (Abernethy &
Jürimäe, 1996; Rutherford et al., 1986; Wilson et al., 1996) it might be
important that training exercises aiming to improve these tasks, and tests
designed to assess performance, have similar movement patterns to the
tasks. With respect to movement-specific adaptations, past research has
shown that adaptations to training, in particular resistance training (RT), are
specific to the body position adopted (Abernethy & Jürimäe, 1996; Raasch &
Morehouse, 1957; Wilson et al., 1996), laterality (i.e. whether the exercise is
performed with one limb or two; Häkkinen et al., 1996; Howard & Enoka,
1991; Tanaguchi, 1997), joint ranges of motion (Kitai & Sale, 1989; Lindh,
1979; Weir et al., 1994) and the mode of contraction (Hortobágyi et al., 1996,
2000; Lacerte et al., 1992; Smith & Rutherford, 1995) of the training
exercises. There is a need therefore to examine the movement patterns of
athletic tasks and resistance training exercises in order to determine
differences in their movement patterns.
Several investigations have examined the movement characteristics of the
56
vertical jump (Bobbert et al., 1986, 1996; Eloranta, 1994; Pandy & Zajac,
1991; Voigt et al., 1995), broad jump (Robertson & Fleming, 1987), sprint run
(Mann & Herman, 1985; Mero & Komi, 1987; Simonsen et al., 1985) and
acceleration phase of a sprint run (Jacobs & Ingen Schenau, 1992; Mero &
Komi, 1990). Also, common resistance training tasks such as the squat lift
have also been well described (McCaw & Melrose, 1999; McLaughlin et al.,
1977; Ninos et al., 1997; Wretengeng et al., 1996). Nonetheless, few
researchers have compared and contrasted the movement patterns of athletic
tasks with movement patterns of resistance exercises (e.g. Canavan et al.
[1996] compared the Olympic clean movement to the vertical jump).
Furthermore, little attempt has been made to describe RT exercises that may
have similar movement patterns to athletic tasks by performing well-controlled
kinematic studies.
The first purpose of this study was to describe and compare the movement
patterns of athletic subjects performing vertical jump (VJ), standing broad
jump (BJ), squat lift (SQ) and jump-squat (JSQ) tasks. The term ‘movement
pattern’ will be used to describe only the timing and magnitude of joint angle
changes (with reference to angular velocities and accelerations) during a
movement. Thus no reference to body position or other factors describing a
movement pattern will be considered in this definition. A second purpose was
to compare the movement patterns of a new exercise, named the forward
hack squat (FHS), and the acceleration phase of a sprint run. Running
acceleration is essential to the performance of many sports so resistance
training exercises that can improve running performance would benefit many
athletes. The FHS was designed in an attempt to augment sprint running
improvements. The acceleration phase of a sprint run was chosen rather than
the maximum velocity phase since 1) the beginning of the acceleration phase
is easy to pinpoint considering it occurs when the subject’s velocity is zero; 2)
resistance training exercises that mimic the movement pattern of the
acceleration phase should be easier to design than those for the maximum
velocity phase; 3) many sports require participants to accelerate rapidly, but
57
not necessarily attain maximum speed; and 4) the acceleration phase of a
sprint run is more often used as a test of dynamic performance in research
studies. Due to space limitations in our laboratory, we were unable to
videotape and complete a kinematic analysis of sprint running. As such, the
kinematics of the FHS was compared to sprint running data published by
Jacobs and Ingen Schenau (1992). This was the only study found to provide
an extensive description of the early acceleration phase of sprinting (second
stance phase) rather than the maximum velocity phase or ‘block’ (starting)
phase. Subjects in that study were seven well-trained male sprint runners
(100 m time = 10.6 ± 0.2 s). Given the subjects in the present thesis were not
elite runners, it cannot be assumed that they would use the same technique in
the acceleration phase as those of Jacobs & Ingen Schenau (1992).
However, they were of similar height and age (see ‘3.2.1 Subjects’).
3.2 METHODS
3.2.1 Subjects
Eight male subjects (age = 25.1 ± [SD] 2.5 yrs, height = 1.81 ± 0.09 m, weight
= 96.3 ± 10.0 kg) volunteered for the study. This subject number was chosen
in order to gain a broad description of movement patterns for the chosen
tasks; many biomechanical analyses have used fewer than eight subjects
(e.g. Bobbert & Van Soest, 1994; Bobbert et al., 1996; Mero & Komi, 1987,
1994; Robertson & Fleming, 1987; Simonsen et al., 1985). The height and
age of subjects were similar to those presented in Jacobs and Ingen Schenau
(1992; age 23 ± 2 yrs, height = 1.84 ± 0.06 m) and would allow good
comparison of resistance training movement patterns to the acceleration
phase of the sprint run as described by those authors. All subjects had
performed regular, heavy weight training at least three times a week for at
least one year prior to participation in the study. They also regularly
participated in sports involving jumping and running. Prior to participation,
58
subjects were briefed on the study, read and signed statements of
Informed Consent and performed at least three familiarisation trials of each
test exercise. The study was approved by the Southern Cross University
Human Experimentation Ethics Committee (see Appendix A).
3.2.2 Overview
Subjects performed a standard warm-up including five minutes of stationary
cycling at a self-selected workload and three to five trials each of a VJ, BJ, SQ
with a load of 60% of bodyweight and FHS with no load added to the sled (the
FHS exercise is described later). Reflective markers were placed on the body
landmarks (see Table 3.1). Subjects then performed three maximal trials of
single- and double-leg VJ and BJ with their arms in different positions, SQ and
JSQ with different loads, and single- and double-leg FHS with different loads.
Subjects rated their performance in each trial and poor trials (i.e. those in
which the subject failed to perform maximally or considered himself
unbalanced) were repeated. The order of exercises was the same for all
subjects. To minimise fatigue subjects rested for one minute between trials of
the same task and three minutes between sets of different tasks. The
movements were recorded by a high-speed video camera (200 Hz) and data
sets relating to joint movement (joint angular displacement, velocity and
acceleration) were calculated after digitising joint markers using Peak Motus
software.
3.2.3 Videography
3.2.3.1 Body landmarks
59
After the standard warm-up, reflective markers (2 cm diameter) were
placed on landmarks on the subjects’ head, arms, trunk and legs (Table 3.1).
All markers were placed on the right side of the body and subjects performed
all movements with their right side to the camera. For SQ and JSQ, the 7th
cervical vertebra (C7) was obscured from view. Therefore, a rigid extension
was placed on the weightlifting bar that allowed an accurate estimation of C7
position. Calculation of C7 position by this method is described in detail later.
3.2.3.2 Camera set-up and video recording
A high-speed video camera (Peak HSC-200, Peak Technologies, Inc. USA)
operating at 200 Hz was placed 12 m from the subject and a one-metre scale
rod was placed at the subject’s feet for later calculation of the scaling factor.
A 1000 W lamp was placed adjacent to the camera and shone on the subject
to increase the contrast of the reflective markers relative to the background
(Burgess-Limerick et al., 1993). The camera was 1.8 m off the ground and
recorded the sagittal view to clearly capture the subject’s head (TMJ; Table
3.1) marker during the squat lift when weights on the bar often obscured it.
The distant camera positioning (12 m) was used to minimise parallax error
created by the high placement of the camera. Camera settings are described
Table 3.1. Landmark names and marker positions forreflective markers.
Landmark Marker PositionHead Temporomandibular joint (TMJ)Neck 7th Cervical vertebra (C7)Shoulder Glenohumeral jointElbow Elbow axisWrist Ulnar styloidAnterior pelvis Anterior superior iliac spinePosterior pelvis Posterior superior iliac spineHip Greater trochanterKnee Femoral condyleAnkle Lateral malleolusHeel Lateral posterior calcaneusToe Metatarsal head II
60
in Table 3.2. These settings allowed high resolution of markers and
optimum field of view for capturing the movements. Once the video was set
up for each subject, the camera was not moved or adjusted for the duration of
testing.
Prior to each task being performed, subjects were viewed at 50 Hz on a
Gateway EV 700 Monitor (Gateway, USA) to ensure the subject was in full
view of the camera. The frame rate was then increased to 200 Hz and the
images of tasks recorded on videotape (Panasonic XD Pro S-VHS,
Panasonic, Japan). Recording began two seconds prior to each movement
and ended two seconds after completion. Video images were recorded by a
Panasonic AG 5700 videocassette recorder (Panasonic, Japan) for later
analysis.
3.2.4 Description of movement tasks
3.2.4.1 Vertical jumps
Subjects performed three trials of a single-leg jump with arm swing and three
trials of four different double-leg countermovement vertical jumps. The hand
positions were varied across trials; the VJ techniques are described in Table
3.3. Changing the hand positions was expected to alter the distance of the
body’s centre of mass from the hip joint and possibly change the movement
pattern adopted by the subjects. It would then be possible to compare the
movement patterns used in performing these different jumps to the movement
Table 3.2. Camera settings during dataacquisition.
Characteristic Camera settingFrame rate 200 HzShutter speed 1/1000 sAperture 2.8 f-stopsFocal length 3×Distance (d) 12 m
61
pattern used to perform the squat exercises.
On instruction the subjects performed the designated jump for maximum
height; a countermovement was allowed prior to the upward. Subjects
descended until their internal knee angle was approximately 100o (± 10o).
Jumps were practiced prior to testing however no mechanical device was
used to ensure the correct knee angle was adopted. Trials where the knee
angle varied by more than 10o from the requested angle were disqualified
from later analysis.
3.2.4.2 Broad jumps
One version of a single-leg BJ and three versions of the double-leg BJ were
performed. The jumps are described in Table 3.4. Subjects performed three
trials of each jump for maximum horizontal distance. No other stipulation was
made regarding the jump’s performance so the subjects performed the jumps
naturally.
Table 3.3. Description of vertical jump techniques. The jumps were performed in the orderpresented here.
Jump DescriptionSingle-leg with arm swing Jump was performed unilaterally. The arms were free to
swing during the jump.Double-leg with arm swing Jump was performed bilaterally. The arms were free to swing
during the jump.Double-leg with hands onhead
Jump was performed bilaterally. The hands were placed onthe head and the elbows faced forward to stop the TMJmarker being obscured.
Double-leg with armsacross chest.
Jump was performed bilaterally. The arms were crossed overthe chest with hands on opposite shoulders. The right wristwas supinated to ensure the wrist marker was visible duringthe jump.
Double-leg with hands onhips
Jump was performed bilaterally. Hands were placed on thehips at the level of the Iliac crest so that the pelvic/hip markerswere not obscured.
62
3.2.4.3 Free-weight barbell squat lift
Subjects performed three squat lifts at each of three weights. First, weights
were placed on a 20 kg Olympic weightlifting bar such that the combined load
equalled 60% of bodyweight. With the loaded bar resting across the
shoulders level with the 7th cervical vertebra (C7), subjects squatted until the
internal knee angle was approximately 100o before moving back to the
starting position. Pilot testing showed that subjects often perform
countermovement jumps to a 100o knee angle. As such, movement
instructions for the SQ and VJ movements were the same. Subjects had
practiced lowering the weight to a knee angle of 100o during the warm-up and
lifts were disqualified from analysis if the knee angle was not within 10o of the
stipulated angle. The subjects were also asked to perform the movement in a
total of two to four seconds with equal time devoted to the downward and
upward phases. After three trials, they repeated the efforts with loads equal
to 100% and 140% of bodyweight. It was hypothesised that changing the
weight lifted would change the movement pattern used for the task since the
centre of mass of the weight-body system would be higher at the higher loads.
Table 3.4. Description of broad jump techniques. The jumps were performed in the orderpresented here.
Jump DescriptionSingle-leg with arm swing Jump was performed unilaterally. The arms were free to
swing during the jump.Double-leg with arm swing Jump was performed bilaterally. The arms were free to swing
during the jump.Double-leg with armsacross chest.
Jump was performed bilaterally. The arms were crossed overthe chest with hands on opposite shoulders. The right wristwas supinated to ensure the wrist marker was visible duringthe jump.
Double-leg with hands inhips
Jump was performed bilaterally. Hands were placed on thehips at the level of the Iliac crest so that the pelvic/hip markerswere not obscured.
63
3.2.4.4 Jump-squat
Three repetitions of a JSQ were performed with a load equal to 60% of
bodyweight. Thus comparisons were possible between JSQ and SQ
movement patterns since both were performed with a load of 60% of
bodyweight. The JSQ was performed similarly to SQ except subjects
performed the concentric phase of the movement with maximal effort. As
such the subject’s feet left the ground during the upward phase. As for VJ,
subjects were asked to descend until the internal knee angle was 100o and
jump for maximum height. Trials where the knee angle varied by more than
10o from the requested angle were disqualified from later analysis.
3.2.4.5 Forward hack squat (FHS)
The FHS was performed in a semi-prone position by lowering and raising a
weight placed on a sled that moves on rails. The exercise was called the
‘forward hack squat’ because the direction of the movement of the weight is
similar to the semi-supine hack squat exercise performed by many weight
trainers. The double-leg FHS is shown in Figure 3.1 and the single-leg
variation is shown in Figure 3.2. Subjects performed five different FHS tasks
including double-leg FHS with 60%, 100% and 140% of bodyweight added to
the 74 kg sled and single-leg FHS with no weight and 50% of bodyweight
added to the sled. Despite the different movement characteristics of SQ and
FHS exercises, pilot testing in our laboratory showed that forces produced at
loads of 60%, 100% and 140% of bodyweight were similar for the SQ and
FHS exercises.
64
Subjects lowered the weight until their internal knee angle was 100o and then
lifted the weight back to the starting position. A 100o knee angle was chosen
since research by Jacobs and Ingen Schenau (1992) showed this to be the
smallest knee angle achieved during the acceleration phase of a sprint run,
and subjects moved to this knee angle during the VJ and SQ exercises. Thus
more accurate comparisons could be made between the FHS, SQ, VJ and
sprint movements. While the eccentric phase was completed in one to two
seconds (so that the contribution of the stretch-shorten cycle to the movement
was consistent across trials) the concentric phase was always performed in
less than one second. For the single-leg FHS (Figure 3.2), the ‘free’ leg was
extended straight backwards during the eccentric phase but became flexed at
the hip and knee during the concentric phase.
Figure 3.1a. The forward hack squat (FHS)
exercise was performed in a semi-prone
position by first lowering a sled (onto which
weights were placed) until the internal knee
angle was approximately 100o. The sled is
placed on rollers and moves along a central
rail. Notice that the internal hip angle is less
than 90o in this position.
Figure 3.1b. After lowering the sled it was
then moved back to the starting position in
preparation for the next repetition.
65
3.2.5 Analysis of video data
The video recordings of each trial were replayed and captured as digital video
by a computer and marker positions digitised using Peak Motus software
(Peak Performance Technologies, USA). Spatial models were designed as
described below and a calibration factor was calculated by the software after
digitisation of the scale rod. Calibration was performed for every movement
for every subject since the subjects’ positions at the beginning of the
movement could not be held perfectly constant. The digitised data was
scaled according to the calibration factor and filtered to remove high
frequency noise before missing data was interpolated and new data sets
formed (see below). From the new data sets, angular displacement, velocity
and acceleration were calculated and compared between tasks.
3.2.5.1 Spatial model
A spatial model was designed to describe the body landmarks, body
segments and joint angles. Body landmarks corresponding to the marker
Figure 3.2. The single-leg forward hack squat was performed as per the double-leg
version except that the ‘free’ leg is extended behind the body in the descending phase and
then flexed (as seen here) in the ascending phase. As such, the movements of the legs
are more similar to those in the acceleration phase of sprint run.
66
placements described above were defined. From these, body segments
and joint angle definitions were described as shown in Tables 3.5 and 3.6
respectively. For the squat lift and jump-squat tasks, the C7, wrist, elbow and
shoulder markers were obscured by the weights added to the bar. In the
spatial model for the squat lifts, these markers were not described, but were
labelled and designated as a ‘virtual point’. The positions of these markers
were estimated by an alternate method (see below).
3.2.5.2 Calculation of virtual point position
A 40 cm inflexible extension was placed on the centre of the bar and
protruding perpendicularly from it. Two reflective markers of 1.5 cm diameter
were set 29.2 cm (proximal marker) and 38 cm (distal marker) from the outer
border of the bar on the side opposite to the extension (see Figure 3.3). The
Table 3.6. Joint angle definitions.
Joint angle DefinitionPelvis-thigh Angle calculated clockwise from pelvis segment to thigh segment. Hip
flexion decreases the angle.
Hip Vector from the knee to greater trochanter to C7. Hip flexion decreasesthe angle.
Knee Anatomical 180o angle between the greater trochanter, knee and ankle.Knee flexion increases the angle.
Ankle Anatomical 90o angle calculated clockwise from the foot segment to the legsegment. Dorsiflexion decreases the angle.
Table 3.5. Body segment definitions.
Segment label Proximal marker Distal markerHead/neck C7 Temporomandibular joint (TMJ)Trunk C7 Greater trochanterUpper arm Shoulder ElbowForearm Elbow WristPelvis Anterior superior iliac spine Posterior superior iliac spineThigh Greater trochanter Knee
Leg (shank) Knee Ankle
Foot Heel Toe
67
markers formed a straight line and the bar rested on the C7 vertebra (the
position of the bar was checked prior to all SQ and JSQ trials) so that a ‘virtual
point’ could be calculated that was situated on the line made by the markers
and at a distance of a certain number of multiples of the distance between the
two markers. These markers were digitised, their raw coordinates exported to
a spreadsheet and the coordinates of the virtual point calculated. The x-
coordinate was calculated by the equation:
x-coordinate = [(xdist – xprox) × 3.32] + xprox ....................(1)
where xdist is the horizontal distance (distance in the x plane) from the bar to
the distal bar extension marker, xprox is the horizontal distance from the bar to
the proximal bar extension marker, and 3.32 represents multiples of the
distance between the two markers described above and shown in Figure 3.
The y-coordinate was similarly calculated by the equation:
y-coordinate = [(ydist – yprox) × 3.32] + yprox .................... (2)
where ydist is the vertical distance (distance in the y plane) from the bar to the
distal bar extension marker, yprox is the vertical distance from the bar to the
A
Reflective markers placed 29.3 cm and 38cm from the opposite surface of the weightbar (point A).
Bar extension (40 cm long).
Figure 3.3. A bar extension was placed on the weight bar. Reflective markers placed onthe bar were later digitised. The position of C7, shoulder, elbow and wrist landmarkswere calculated by equations (1) and (2) and imported into the original filtered data setsas ‘virtual’ point data.
68
proximal bar extension marker, and 3.32 represents the multiples of the
distance between the two markers as described above and shown in Figure
3.3. Once the x- and y-coordinates of the virtual point were calculated, the
data were imported back into the trial data. A moving stick figure was created
from the raw data and the movement of the virtual point inspected to ensure
its correct calculation. The virtual data were used for the coordinate positions
of the C7, shoulder, elbow and wrist markers. While the bar rested across the
shoulders and was placed adjacent to the C7 vertebra, and the wrist marker
was in close proximity to the bar, the elbow was approximately 10 - 15 cm
from the bar. The distance from the elbow to the bar was minimised by
subjects placing their hands wide on the bar, however some error would have
occurred when using the virtual data as a description of the location of the
elbow joint. The error was consistent across all SQ and JSQ trials since the
subject’s hand positions were held constant.
3.2.5.3 Digitisation procedure
After the spatial model was described a 0.05 s segment of video sequence
containing the scaling rod was captured. The scaling rod was manually
digitised and a calibration factor calculated by the software. Subsequently, a
three second segment of video of the same movement, encapsulating one
subject performing one task, was captured and cropped approximately 0.1 s
(equal to 20 frames) either side of the start and end points of the movement.
Landmarks were digitised using the auto-tracking facility with parabolic
automatic point prediction. The automatic digitisation procedure was watched
carefully to ensure marker confusion did not occur and markers were not
digitised when invisible (i.e. markers positions were not guessed when
obscured from view). Gaps in the raw position data that resulted from these
periods of marker obscurity were filled by mathematical interpolation (Peak
Motus, Peak Performance Technologies, USA) when the period of marker
obscurity lasted less than one-sixth of movement time. Trials were discarded
from analysis if gaps longer than one-sixth of movement time were found for
any marker.
69
Raw data sets (including virtual point data) for all tasks were filtered using a
4th order, zero-lag Butterworth filter with a 6 Hz cut-off frequency. A cut-off
frequency of 6 Hz was chosen since the movement frequencies of human
subjects rarely exceed this value. A cut-off frequency of 6 Hz has been used
previously when analysing human lifting techniques (Burgess-Limerick et al.,
1993; Kromodihardjo & Mital, 1987) and similar cut-off frequencies have been
used in the analysis of high-speed movements (Gregor et al., 1985; Vint &
Hinrichs, 1996; Voigt et al., 1995). The filtered, raw coordinates were scaled
using the previously determined scaling factor and calculations of joint angular
displacements, velocities and accelerations performed.
3.2.6 Statistical Analysis
Means and standard deviations were calculated for joint angle, angular
velocity and angular acceleration data sets from the eight subjects. To
compare movements two methods were used. First, the times to complete
16%, 33%, 50%, 66% and 84% of a movement were calculated and graphed
against movement time (normalised to 100% of movement time). For this
analysis, the first and second phases of a movement were calculated
separately such that mid-movement occurred at 50%. Then 16% and 33% of
movement were calculated at 33% and 66% of the first (descending) phase.
66% and 84% of movement were calculated at 33% and 66% of the second
(ascending) phase. For example, if the knee angle for a movement moved
through a range of motion of 60o during the descending phase (i.e. 0 – 60o of
knee flexion) and then 70o (60 – -10o) during the ascending phase of a
movement, then 16%, 33%, 50%, 66% and 84% of the total movement
occurred at 20o, 40o, 60o (during knee flexion), 46.2o and 23.1o (during knee
extension).
The second method used to compare movements was by statistical analysis.
There are several methods that can be used to compare curves, however
70
none are without fault. For simplicity, curves were broken into sections
representing 5% of movement time and compared using paired t-tests (since
the same subjects performed all movements). This method has been used
previously in research investigating the sprint run (Weimann & Tidow, 1995).
Due to the large number of t-tests, the Bonferroni-corrected alpha level was
reduced to 0.0025 (for an overall alpha level of 0.05) making significant
differences very difficult to detect and the statistical analysis overly
conservative. In such instances (i.e. where the universal null hypothesis is not
of interest) Bonferroni correction is not warranted as important information
may be lost after analysis (Perneger, 1998). Thus Bonferroni correction was
not performed.
3.3 RESULTS
3.3.1 General Movement Descriptions
The movement patterns of subjects performing SQ, FHS, VJ and BJ tasks are
shown in Figures 3.4 – 3.7. Only one version of each exercise will be
described here, a comparison of different versions of each exercise will follow.
In these figures a decrease in angle of the hip and ankle joints represents joint
flexion, while an increase in knee joint angle represents joint flexion. This is
because the internal hip and ankle angles, but the external knee angle, are
shown to minimise overlap of hip and knee graphs and improve clarity.
Nonetheless, for all joints (hip, knee and ankle) an increase in angular velocity
or acceleration is shown as a positive inflection in the graph.
3.3.1.1 Squat lift
The movement pattern of a SQ performed with a load equal to bodyweight
resting across the shoulders is shown in Figure 3.4. The general movement
patterns for squats with loads of 60% and 140% were similar and therefore
71
will not be presented here. From the starting (standing) position the hip, knee
and ankle joints flexed simultaneously and the body moved to a squatting
position. The angular acceleration of the joints was small throughout this
descending phase. At the transition from descending to ascending phases
the hip and knee angles (mean ± SD) were 92 ± 9o and 98 ± 7o (82o internal
knee angle) respectively. Ankle dorsiflexion was greatest at –30 ± 6o at this
transition point. Almost as a mirror image of the descending phase, the
ascending phase was also characterised by simultaneous extension of the
hip, knee and ankle joints and no rapid accelerations. The body finished in
the original, upright position.
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ocity
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1 26 51 76 101 126 151 176 201Jo
int A
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.s-2
)
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deg)
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eg.s
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1 26 51 76 101 126 151 176 201
Join
t Ang
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Acc
eler
atio
n(d
eg.s
-2)
Time (0.5% intervals)
Figure 3.4. Movement pattern of the squat liftexercise. The exercise is characterised bysimultaneous movements of the hip, knee andankle joints. The angular velocities of these jointsmirrored each other although higher angularvelocities occurred at the knee because of itslarger range of motion. Error bars representstandard deviation.
Figure 3.5. Movement pattern of the forwardhack squat (FHS) exercise. While similar to thesquat lift, ankle plantarflexion occurred after hipand knee extension. Thus the FHS appears ahybrid of push-like and throw-like movementpatterns. Error bars represent standard deviation.
72
3.3.1.2 Forward Hack squat
The movement pattern for a bilateral FHS with a weight equal to bodyweight
placed on the sled of the machine is shown in Figure 3.5. The different
movement pattern adopted during FHS compared to SQ was expected given
the constraints of the FHS machine. Similar to SQ the hip, knee and ankle
joints flexed simultaneously. However while the hip angle reached a minimum
of 102 ± 13o (i.e. only slightly more open than during SQ) the smallest knee
angle was 81 ± 7o (99o internal knee angle), 17o more closed than for SQ.
Therefore, compared to SQ, the movement pattern of FHS is one where hip
flexion is greater than knee flexion in the descending phase of the movement.
The ankle range of motion was also different. While identical minimum ankle
angles were achieved during both SQ and FHS tasks (the minimum ankle
angle for FHS was 30 ± 6o), ankle plantarflexion occurred much later in the
FHS movement. The different timing of ankle angle changes can be observed
clearly in the angular velocity and acceleration graphs. The increase in
angular velocity and acceleration occurred after the peak in hip and knee
angular velocity and acceleration. Therefore, while movement about the hip
and knee joints occurred simultaneously, movement at the ankle was delayed.
3.3.1.3 Vertical jump
The movement pattern for a VJ with arms placed across the chest (VJ ac) is
shown in Figure 3.6. Unlike the RT exercises, a larger proportion of the
movement time was devoted to the descending phase of the movement as a
consequence of the high vertical velocity of the centre of gravity achieved
during the ascending phase. The magnitude of joint angle changes however
were similar to those of SQ (the smallest hip, knee and ankle angles were 98
± 10o, 97 ± 9o and 33 ± 4o respectively). Possibly the most striking difference
between the VJ and resistance exercises was the timing of joint angle
73
changes. In the VJ, the hip angular velocity increased before the knee and
ankle (middle graph, Figure 3.6) although all joints reached their peak angular
velocity at the same time (immediately prior to toe-off). Thus the VJ
movement pattern exhibited sequential extension of joints from proximal to
distal consistent with a throw-like movement.
3.3.1.4 Broad jump
The movement pattern for a BJ with arms placed across the chest (BJ ac) is
presented in Figure 3.7. Similar to the VJ, angular accelerations and
velocities were far higher than for the resistance exercises, however the
Time (0.5% intervals)
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0
50
100
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Join
t Ang
le (
deg)
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Join
t Ang
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ocity
(deg
.s-1
) Hip
Knee
Ankle
-10000-8000-6000-4000-2000
0200040006000
1 26 51 76 101 126 151 176 201
Join
t Ang
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Acc
eler
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(deg
.s-2
)
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t Ang
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t Ang
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ocity
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.s-1
) Hip
Knee
Ankle
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02000
40006000
1 26 51 76 101 126 151 176 201
Join
t Ang
ular
Acc
eler
atio
n
(deg
.s-2
)
Time (0.5% intervals)
Figure 3.6. Movement pattern of the verticaljump. The exercise was characterised by largeaccelerations of the hip, knee and ankle joints.The angular velocities of these joints reached theirmaxima simultaneously. Error bars representstandard deviation.
Figure 3.7. Movement pattern of the broad jump.The hip extended early in the ascending phase toreach a higher angular velocity than the knee andankle joints. Error bars represent standarddeviation.
74
changes in joint angles were unlike any other movement described thus
far. The hip angle rapidly closed during the descending phase, followed later
by the knee then ankle joints. The smallest hip angle was 85 ± 20o in the
transition from descending to ascending phases. While this is smaller than for
other movements it was highly variable. The knee and ankle angles later
closed to 82 ± 14o (98o internal knee angle) and -36 ± 7o respectively. The
ascending phase began with rapid extension of the hip joint (see middle and
bottom graphs, Figure 3.7) before the lagging knee and ankle joints extended.
Unlike all other movements, the highest angular velocities occurred at the hip,
rather than the knee. Thus, while the BJ was similar to the VJ in that joint
extensions occurred sequentially, the BJ movement pattern was very different
to the other movements described previously.
3.3.2 Comparisons of Task Movement Patterns
Comparisons between tasks are shown in Figures 3.8 – 3.13. Each
movement is divided into the phases previously described. For example, the
16% bin on the x-axis represents that part of the movement where subjects
were 16% of their way through the total movement, or 33% of their way into
the descending phase. The 50% mark represents the transition period
between descending and ascending phases. The 84% mark represents that
part of the movement where subjects were 84% of their way through the total
movement, or 66% of their way through the ascending phase. The phase of
movement is plotted against the total movement time (y-axis). As such, these
are displacement versus time graphs. A steep gradient suggests that the
subjects were moving slowly (i.e. they took more time to move through the
movement phases). In contrast, a flatter gradient suggests that subjects were
moving more quickly in that part of the movement (that is, they moved
considerable distance in little time). Error bars were omitted to improve
clarity. Further statistical comparisons will be presented later.
75
3.3.2.1 Squat lift comparisons (SQ versus JSQ)
The movement pattern of JSQ differed from the traditional squat lifts (SQ +
60% and SQ + 140%; squat with a load of bodyweight is not shown) in that
the descending phase was performed slower than the ascending phase (see
Figure 3.8). Also, while the relative timing of hip angle changes was similar to
the traditional squats, both knee and ankle joint extension was delayed. That
is, the JSQ knee and ankle curves rise early suggesting relatively slower
movement, then flatten toward the end of the movement suggesting more
rapid joint angle changes. The size of this effect was greater for the ankle
than the knee suggesting a sequential extension of joints from hip to ankle.
Thus the movement pattern of the JSQ was different to the traditional squat
lifts.
0%
20%
40%
60%
80%
100%
0%
20%
40%
60%
80%
100%
0%
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40%
60%
80%
100%
FHS 1lFHS + 60%
FHS + BW
0%
20%
40%
60%
80%
100%
16% 33% 50% 66% 84%
% Total Movement Time
Knee
Ankle
0%
20%
40%
60%
80%
100%
FHS 1L
FHS + 60%FHS + BW
0%
20%
40%
60%
80%
100%
16% 33% 50% 66% 84%
Phase of Movement
% T
otal
Mov
emen
t Tim
e
Knee
Ankle
0%
20%
40%
60%
80%
100%
0%
20%
40%
60%
80%
100%
JSQ
SQ + 60%SQ + 140%
0%
20%
40%
60%
80%
100%
16% 33% 50% 66% 84%
Phase of Movement
Ankle
Knee
% T
otal
Mov
emen
t Tim
e
Hip
Figure 3.8. Comparison of the jump-squat (JSQ),and squat lifts with 60% (SQ + 60%) and 140%(SQ + 140%) of bodyweight across the shoulders.
Figure 3.9. Comparison of single-leg forwardhack squat (FHS 1L) and forward hack squatswith 60% (FHS + 60%) and 100% (FHS + BW) ofbodyweight added to the sled.
Hip
76
While there was little difference between either of the traditional squat lifts, the
ascending phase of the heavier lift (SQ + 140%) was slower (ie the curve
steeper) than for the lighter squat lift. Such a result would be expected given
the extra force required to move the heavier load.
3.3.2.2 Forward hack squat comparisons
Movement pattern differences between the FHS movements were perhaps
more numerous than for SQ (see Figure 3.9). The single-leg FHS differed to
the lighter FHS (FHS + 60%) in that the ascending phase was longer (ie the
curve was flatter between 50% and 100% of the movement) and
plantarflexion tended to occur more consistently rather than undergoing rapid
acceleration later in the movement. The single-leg FHS also differed to the
heavier FHS (FHS + BW) in that plantarflexion was more consistent. As such,
the single-leg FHS exhibited a very distinct push-like pattern of movement.
There were differences between the two double-leg FHS movements with
knee and ankle motion being slightly delayed early in the descending phase at
the lighter weight (FHS + 60%). There were however no significant
differences between the two tasks in the ascending phase.
3.3.2.3 Vertical jump comparisons
There were few differences between the movement patterns of the vertical
jumps where arms were not free to swing (i.e. on head, chest or hips),
therefore only the VJ with arms across chest and with arm swing are shown in
Figure 3.10. The two movements differed in that hip extension was delayed
at the transition phase and occurred rapidly later in the ascending phase in VJ
with arm swing (VJ wa). There was also a small difference at the ankle with
extension occurring later and more rapidly when the arms were free to swing.
77
Thus, although there were no differences at the knee, there were
differences in the timing of hip extension between the two VJ techniques.
3.3.2.4 Broad jump comparisons
There was little difference between those BJ where arms were (broad jumps
with arm swing; BJ wa) and were not (broad jump with arms across chest; BJ
ac) used. However, like VJ, hip extension was delayed early in the ascending
phase and more rapid toward the end when the arms were free to swing
(Figure 3.11). There were differences however between the double-leg and
single-leg (single leg broad jump; BJ 1L) jumps. Movements at the hip, knee
and ankle joints were more consistent in their changes for the single-leg jump
rather than showing periods of slower and more rapid change.
0%
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40%
60%
80%
100%
0%
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40%
60%
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VJ ac
VJ wa
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16% 33% 50% 66% 84%
Hip
Knee
Ankle
% T
otal
Mov
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% T
otal
Mov
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t Tim
e
0%
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Bj 1LBj acBj wa
0%
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40%
60%
80%
100%
16% 33% 50% 66% 84%
Phase of Movement
Ankle
Knee
Hip
Figure 3.10. Comparison of vertical jumps witharms across the chest (VJ ac) and with arm swing(VJ wa).
Figure 3.11. Comparison of single-leg broadjump (BJ 1L), broad jump with arms across thechest (BJ ac) and broad jump with arm swing (BJwa).
78
3.3.2.5 Vertical jump versus jump-squat
Given the similar magnitudes of joint angle changes between VJac (VJ with
arms across chest) and JSQ, the two tasks were compared for their timing of
joint angle changes. As shown in Figure 3.12, there was little difference
between the movement patterns of the two tasks although relative velocity of
the joint angle changes during the descending phase of the JSQ was slightly
different. This may have been expected given the joint angles of the two
tasks differed slightly at the start of movement causing joint angle changes in
the JSQ to be slightly smaller than for VJac. There was no difference in the
timing of joint angle changes in their ascending phases.
3.3.2.6 Broad jump versus forward hack squat
As the body position during ascending phases of FHS and BJ were similar,
the timing of joint angle changes were compared (see Figure 3.13). There
appeared to be no similarity between the two movements. Their descending
phases were likely to exhibit different movement patterns given that the body
position during the descending phase of a FHS was semi-prone whereas the
body was upright during the BJ. However differences, although minimal at the
ankle, also existed during the ascending phase where the body position and
goal (direction of movement) of the tasks were similar. The FHS cannot
therefore be considered similar to BJ.
79
3.3.2.7 Similarities between squat lift and vertical jump tasks
Given the apparent similarity between different vertical jumps and between VJ
and SQ/JSQ, these movements were further analysed. The joint angle
changes for the VJ with arm swing and with arms across the chest are shown
in Figure 3.14. The significant effect of arm swing on hip range of motion can
be seen with differences (not corrected for experiment-wise error rate)
between the tasks occurring throughout the movement.
0%
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16% 33% 50% 66% 84%
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FHS + BW
BJ ac
Phase of Movement
Ankle
Knee
% T
otal
Mov
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Phase of Movement
% T
otal
Mov
emen
t Tim
e
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VJ acJSQ
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16% 33% 50% 66% 84%
Ankle
Hip
Knee
Figure 3.13. Comparison of forward hack squatwith a load equal to bodyweight added to the sled(FHS + BW) and broad jump with arms across thechest (BJ ac).
Figure 3.12. Comparison of the vertical jump witharms across chest (VJ ac) and jump-squat (JSQ).
80
Both of these jumping styles were compared to the SQ and JSQ. There were
large differences between the VJ with arm swing and all of the squat tasks.
However there was little difference between movement patterns for VJac and
JSQ (Figure 3.15). Other vertical jumps without arms swing (i.e. with hands
on head and with hands on hips) were not as similar as VJac. The main
differences between VJac and JSQ were at the beginning of the movement
(see Figure 3.15). The hip and knee joints were more flexed during a JSQ
possibly due to the load lifted. However, as the movement proceeded the
plots of the joint angles merge. Indeed there was little difference in the joint
angles of hip, knee and ankle between the movements both at the transition
from descending to ascending phases, and during the entire ascending
phase. Differences in the ascending phase were limited only to the point
immediately before toe-off where extension of the hip and ankle joints was
more complete during the VJ. Thus, subjects adopted similar movement
patterns for the performance of JSQ and VJac.
Figure 3.14. Comparison of vertical jumps with arm swing (VJwa) and vertical jumps witharms across chest (VJ ac). Both the timing and magnitude of hip joint angle changes weredifferent between the two tasks (* indicates p<0.05). There was little difference at the kneeand ankle joints although the vertical jump with arms across the chest was characterised byslightly less plantarflexion at the end of the ascending phase (# indicates p<0.05). Error barswere omitted to aid readability but standard deviations were similar to those in Figure3.7.
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100
150
200
0 20 40 60 80 100
Percent of Movement Time (%)
Join
t Ang
les
(deg
rees
)Hip angle VJwa
Knee angle VJwa
Ankle angle VJwa
Hip angle VJ ac
Knee angle VJ ac
Ankle angle VJ ac
*
#
*
*
81
3.3.2.8 Similarities between the forward hack squat and acceleration
phase of sprint running
Given the dissimilarity of FHS and BJ movement patterns, the timing and
magnitude of joint angle changes for the concentric phase of a FHS were
compared to those of the acceleration phase of a sprint run described by
Jacobs and Ingen Schenau (1992). While the data for the sprint run were not
available, some comparisons could be made to the joint angle curves
presented by the authors (Figure 3.16). There appeared to be good
agreement in the joint angle curves for the hip and knee joints. Both tasks
were characterised by smaller joint angle changes early in the concentric
phase but more rapid changes later. Further, the joint angular velocity curves
(curves for the sprint run are not presented here) were similar in that the
-50
0
50
100
150
200
0 20 40 60 80 100
Percent of Movement Time (%)
Join
t Ang
les
(deg
rees
)
Hip angle JSQ
Knee angle JSQ
Ankle angle JSQ
Hip angle VJ ac
Knee angle VJ ac
Ankle angle VJ ac
*
*
+
#
#
Figure 3.15. Comparison of the jump-squat (JSQ) and vertical jump with arms across chest (VJ ac).While there is a small but significant difference in joint angles at the start of the movements, their timingof joint angle changes, and magnitude of joint angles at the point of transition from descending toascending phases are almost identical. Subjects starting from a more upright position in the JSQ couldmake the two tasks more similar. * - hip angles significantly different, + - knee angles significantlydifferent, # - ankle angles significantly different (p<0.05). Error bars were omitted to aid readability, butstandard deviations were similar to those presented in figures 3.5 and 3.7.
82
greatest angular velocities occurred at the knee joint. The hip and knee
joints attained their maximum angular velocity simultaneously with the
maximum at the ankle occurring marginally later. Greater differences were
seen in the range of motion of the ankle with plantarflexion being greater at
the start and end of the concentric phase in the sprint run. In order to perform
the FHS more similar to the sprint run, subjects could have plantarflexed more
at these points during the movement.
Joint angles during a Forward Hack Squat with weight
1
1.5
2
2.5
3
3.5
Hip
Ang
le (
radi
ans)
1
1.5
2
2.5
3
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Kne
e A
ngle
(ra
dian
s)
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3
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0 20 40 60 80 100
Percent of Push-off Time (%)
Ank
le A
ngle
(ra
dian
s)
Joint angles during a sprint push-off. Adapted from Jacobs and Ingen Shenau,
1992.
1
1.5
2
2.5
3
3.5
Hip
Ang
le (
radi
ans)
1
1.5
2
2.5
3
3.5
Kne
e A
ngle
(ra
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1
1.5
2
2.5
3
3.5
180 160 140 120 100 80 60 40 20 0
Time (ms)
Ank
le a
ngle
(ra
dian
s)
Figure 3.16. Comparison of joint angle changes for the forward hack squat (FHS) andacceleration phase of a sprint run (adapted from Jacobs & Ingen Schenau, 1992). Anglesare presented in radians as per Jacobs & Ingen Schenau (1 radian = 57.3o). Hip and kneepatterns were very similar while the ankle angle differed largely at the start and end of thepushing phase.
83
3.4 DISCUSSION
The purpose of this study was to compare the movement patterns of subjects
performing VJ and BJ to their movement patterns during the squat lift (SQ and
JSQ) and FHS exercises. This discussion will not directly compare the
movement patterns of these tasks to those described in previous studies, but
focus on comparing the movements presented here with the aim of finding
resistance exercises that are similar in movement pattern to the VJ and BJ,
and the acceleration phase of the sprint run.
The VJ is performed bilaterally and in an upright position and was therefore
first compared to the SQ. During the descending phase of the VJ, joint angle
changes occurred simultaneously with flexion of the hip, knee and shoulder
joints. However these joints opened sequentially (from hip to ankle) during
the upward phase. Nonetheless, the angular velocities of these joints
reached their maxima simultaneously immediately prior to toe-off. Such a
movement pattern has been previously reported for the vertical jump (Bobbert
et al., 1986; Pandy & Zajac, 1991; Voigt et al., 1995).
Since two different styles of VJ were analysed, one where the arms were free
to swing (vertical jump with arm swing; VJwa) and the other where the arms
were held stationary (in fact three versions of the latter were also compared),
variations of the VJ were examined. Most notably, the two jumping styles
differed in that the hip angle of VJwa was smaller (more closed) at the
transition from descending to ascending phases. While its effect has not been
directly examined in the literature, the increase in range of motion of the hip
would possibly cause an increase in hip extensor moment. Some authors
have suggested that the increased hip moment, or rather the increase in joint
power from this, would be transferred by biarticular muscles to the ankle
culminating in an increase in ankle plantarflexor moment and an increase in
jump height (Bobbert & Ingen Schenau, 1988, 1992; Van Soest et al., 1993).
84
SQ was often performed by simultaneous flexion of the hip, knee and ankle
joints during the descending phase and then simultaneous extension during
ascent. The timing of joint angle changes was therefore different to either of
the two VJ styles. Although there was a difference in the hip angle at
transition from descending to ascending phases between VJ and SQ, there
was little difference between the magnitude of joint angle changes. However,
it cannot be concluded that the movement patterns adopted during VJ and SQ
tasks were the same.
There was little difference between movement patterns of JSQ and VJac.
Since the jump-squat is performed with a maximal ascending phase, the JSQ
and VJac had the same sequence of joint angle changes (i.e. hip before knee
before ankle). Furthermore, as illustrated in Figure 16, there was little
difference in joint angles at the transition from descending to ascending
phases. Probably the greatest difference between the two tasks was at the
movement’s beginning where joints were more closed during the JSQ. This
was likely a result of subjects squatting slightly under the load of the barbell
prior to the jump. Nonetheless, VJac could be considered very similar to the
JSQ since they were both performed bilaterally, in an upright body position
and the magnitude and timing of joint angle changes were very similar. How
the movement pattern of subjects performing the JSQ would change if heavier
loads were used is unclear from the present research.
The BJ is performed bilaterally from an upright position although the
ascending phase has a large horizontal component. In contrast to previous
research (Robertson & Fleming, 1997), the hip, knee and ankle joints
extended sequentially during the ascending phase. However, as reported
previously, the change in hip joint angle (and possibly contribution to total
torque) was far greater than the change at the knee (Robertson & Fleming,
1997) although the knee angular velocity was very high (Aguado et al., 1997).
As it is difficult to perform the SQ with such a movement pattern the FHS was
analysed and subjects’ movement patterns compared to those for the BJ.
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BJ’s performed with arm swing were different to those without in that the
hip angle was lesser at the transition from descending to ascending phases.
The movement pattern of the double-leg BJ exhibited a sequential pattern
rather than they’re being simultaneous joint angle changes. These
characteristics are the same for the FHS so it was compared to the BJ.
The double-leg FHS was characterised by simultaneous extension of hip and
knee joints, but delayed ankle extension making it a hybrid of the throw-like
and push-like movement patterns often used to describe movements. The
single-leg FHS was characterised by simultaneous extension of the hip and
knee joints but a slower and more consistent change at the ankle joint. The
magnitude of joint angle changes were however not different between one-
and double-leg versions. The movement patterns of the FHS and BJ were
therefore not the same. Also, the magnitude of joint angle changes between
the FHS and BJ was very different. Thus, despite the two tasks being similar
in their laterality (i.e. both tasks can be performed unilaterally or bilaterally)
and the body position adopted during the ascending phase, the timing and
magnitude of joint angle changes were very different. The movement pattern
that characterised the FHS was therefore different to the BJ.
Given the dissimilarity of the FHS and BJ, the FHS was compared to the
acceleration phase of a sprint run. Due to space limitations in our laboratory,
the sprint run could not be kinematically analysed. Therefore the movement
pattern of the FHS was compared to the previously published data of Jacobs
and Ingen Schenau (1992). Qualitative comparison on the timing and
magnitude of joint angle changes for the two tasks showed that their
movement patterns were more similar than to the VJ or BJ. The greatest
difference between the two tasks was at the end of the push-off phase of both
movements where the sprint run is characterised by more prominent ankle
plantarflexion. Nonetheless, subjects in the present study performed the FHS
task without any instruction as to the level of plantarflexion required.
Plantarflexion at the end of the movement could probably be increased
86
significantly by these subjects without affecting the movement pattern of
the hip and knee joints.
The hip and knee joints extend simultaneously early in the push-off phase of
sprinting presumably to rotate the body forward before more rapid and
sequential extension of all three joints occurs later in the movement (Jacobs &
Ingen Schenau, 1992). A similar timing of joint angle changes was seen in
the ascending phase of the FHS. Further, the time at which the maximum
angular velocity of the joints occurred was also identical. Given therefore that
the timing and magnitude of joint angle changes were similar (and could be
made more similar with greater plantarflexion late in the pushing phase of the
FHS), both tasks can be performed unilaterally and the body is semi-prone in
the pushing phase of both movements, the movement pattern adopted for the
FHS and acceleration phase of sprint running appear very similar. Research
using the same subjects performing both tasks is necessary to more precisely
examine similarities and differences between the two movements.
In conclusion, the movement patterns of different exercises changed as the
constraints of the exercises (i.e. use of arm swing, load lifted, laterality, etc.)
were changed. This increased the number of movement patterns that could
be compared in order to find resistance exercises that could be considered
similar to VJ, BJ, and the acceleration phase of sprint running. Indeed, the
JSQ was very similar to the VJ without arm swing (especially when the arms
were crossed over the chest), although the effect of lifting greater JSQ loads
was not addressed in this study. Also, within the confines of the research
performed, one might conclude that the movement patterns of the FHS and
acceleration phase of a sprint run are also very similar. Given the movement
pattern specific adaptations to RT, the newly developed FHS exercise may be
a superior training exercise than SQ, JSQ or VJ to enhance sprint running
acceleration.
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RELIABILITY AND VALIDITY OF ISOMETRIC
SQUAT AND FORWARD HACK SQUAT TESTS
4.1 INTRODUCTION
Research studies investigating adaptations to weight training often
incorporate the barbell squat as a dominant training exercise (Baker et al.,
1994; Delecluse et al., 1995; Häkkinen & Komi, 1983; Häkkinen et al., 1985a;
Thorstensson et al., 1976; Willoughby, 1993; Young & Bilby, 1993).
Nonetheless, despite research suggesting that the mode (contraction type:
isometric, concentric, eccentric) and movement pattern of strength tests
should be similar to those of the training exercises (for reviews see:
Abernethy et al. [1995] and Morrissey et al. [1995]), relatively few studies use
the 1-RM (one repetition maximum) squat test to determine strength changes
after training (Thorstensson et al., 1976; Willoughby, 1993; Young & Bilby,
1993). Instead, strength changes after squat lift training are often examined
by isometric tests (Häkkinen & Komi, 1983; Häkkinen et al., 1985a, 1987;
Young & Bilby, 1993) which may be preferred for their high test-retest
reliability (Agre et al., 1987; Bemben et al., 1992; Young & Bilby, 1993),
relatively simple administration and reduced risk of injury.
The relationship between dynamic strength increases and isometric strength
is not strong (Baker et al., 1994; Sale et al., 1992). For example, Sale et al.
(1992) found that isometric knee extension strength did not increase after a
19 weeks of leg press training despite muscle hypertrophy occurring over the
training period. Such results are possibly due to the different contraction
modes of training and testing exercises. However, the weak relationship
between changes in the isometric and dynamic tests may also be related to
their different movement patterns. A large body of evidence suggests that
89
adaptations to resistance training are specific to the movement pattern of
the training exercises (Abernethy & Jürimäe, 1996; Rutherford & Jones, 1986;
Thepau-Mathieu et al., 1988; Wilson et al., 1996). Thus, if isometric tests of
strength are to be used in preference to dynamic tests, or to assist in the
provision of training loads, it may be important that the body position adopted
in the isometric test be identical to the training exercise.
Given the SQ is commonly used in studies investigating adaptations to
resistance training, an isometric squat test (ISQ; figure 4.1A) might be a
useful alternative to the 1-RM squat. However, the movement pattern of SQ
is not similar to movements performed in many sports. The isometric FHS
(IFHS; Figure 4.1B) may be used since it allows isometric testing with a
movement pattern similar to sprint running (see Study One).
The purpose of this study was first to examine the reliability of both the ISQ
and IFHS tests to determine if repeated measures on the same subjects
AB
Figure 4.1. Subject position for both the isometric squat (ISQ; A) and forward hack squat
(IFHS; B) tests.
90
yielded reliable results, and second to examine the relationship between
isometric and 1-RM measures of strength. The ISQ test was performed with a
knee angle of 90o and the IFHS test with a hip angle of 90o so that the
subjects were in the lowest position of the movement. It was hypothesised
that the isometric force would be best related to dynamic 1-RM at this position
since it is here that the lifts are most difficult. This study is important in the
context of the thesis since a training study will be conducted. If isometric tests
can be used to predict 1-RM, training loads can be set with minimal effort or
injury risk and an indication of changes in subjects’ 1-RM strength could be
gained.
4.2 METHODS
4.2.1 Subjects
Fourteen athletic males (Age range = 19 – 26 yrs) volunteered to participate in
the study. All played competitive sport at a recreational or representative
level and had at least six months of weight training experience. The research
was approved by the Southern Cross University Human Ethics Committee
and subjects signed a statement of informed consent. They were able to
withdraw from the study at any time.
4.2.2 Testing
Subjects performed ISQ and IFHS tests on two occasions at the same time of
day one week apart. Subjects also performed a 1-RM squat or FHS test on
different testing days so that after two weeks each subject had performed
both the 1-RM squat and FHS tests once. The order of testing was
randomised between subjects to prevent order effects although isometric tests
were always performed before 1-RM tests. All tests followed a warm-up
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including five minutes of moderate intensity running, ten minutes of
stretching and several warm-up repetitions of squat and FHS exercises at
increasing intensity.
4.2.2.1 Isometric squat (ISQ)
Subjects squatted until the internal knee angle was 90o with a 20 kg bar
resting across the shoulders. While in this position, the hip angle was
measured and recorded. Subjects then moved to a Smith Machine (a squat
rack designed to allow the bar to move only in the vertical plane) and squatted
with its bar across their shoulders until their hip and knee angles were
identical to the barbell squat. Metal stops were then placed on top of the bar
to prevent its upward movement. Once bar height was established, subjects
performed two warm-up trials of the isometric squat, one at 60% and one at
80% of their perceived maximum exertion (Figure 4.1). They then performed
three maximal isometric efforts lasting four seconds with three minutes rest
separating each trial. Hip and knee angles were checked prior to each effort
and loud verbal encouragement was given to increase subject motivation.
Force produced during the squat was recorded by a force platform (Kistler
Instrumenté, Switzerland) on which the subject’s feet were placed during each
isometric effort. The position of the feet was recorded for subsequent efforts.
Force was sampled at 1000 Hz and stored on computer (IBM compatible 486
DX) for subsequent analysis.
4.2.2.2 Isometric forward hack squat (IFHS)
The rails along which the sled moves were adjusted to an angle of 39o to the
horizontal. Subjects placed two feet on the foot platform such that the body
formed a straight line from the head to the ankle while in the standing position.
They then lowered the weight until the internal hip angle was 90o and the
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internal knee angle was 110o (Figure 4.1B). This approximated the hip and
knee angles during push-off in the acceleration phase of sprint running
(Jacobs & Ingen Schenau, 1992). A metal peg was used to hold the machine
in this position for the subsequent maximal isometric contractions. Subjects
then lifted the sled slowly until the metal peg stopped its upward movement
and hip and knee angles were checked to ensure they were at 90o and 110o
respectively before the subjects provided two warm-up (60% and 80% of
perceived maximum) and three maximal isometric contractions lasting four
seconds. Three minutes rest separated each maximal effort. Force produced
during the isometric contraction was sampled at 100 Hz by a load cell (Output
= 1.9231 mV/V, hysteresis <0.02%, Model LPS-2KG, Scale Components Pty.
Ltd., Australia) placed parallel to the direction of sled movement. The signal
was fed into a personal computer (IBM compatible 486 DX) and data stored
for later analysis using a custom program written using AMLAB software
(Chatanooga, Inc., USA).
4.2.2.3 1-RM squat
1-RM squat strength (free-weight) was tested by subjects lifting increasingly
heavy weights until a weight could not be lifted. Subjects placed their feet
with the same stance as for the ISQ test and stood with a loaded barbell
across the shoulders. Subjects then squatted until their internal knee angle
was 90o before lifting the weight back to the standing position. The smallest
increment in weight between lifts was 5 kg. At least three minutes separated
each trial.
4.2.2.4 1-RM forward hack squat (FHS)
The position of the subjects’ feet and body, and of the rails on which the sled
moved, were identical to the IFHS. Each FHS trial required the subject to
lower the weight until their internal knee angle was 110o before lifting the
93
weight back to the standing position. Subjects attempted to lift
incrementally heavier weights until a weight could not be lifted. At least three
minutes separated each attempt and the smallest increase in weight between
successive lifts was 10 kg.
4.2.3 Data analysis
Change in the mean between testing session one and two, typical error (i.e.
variance of the change in performance between the two testing sessions),
Pearson’s Product Moment Correlations and Intraclass Correlation
Coefficients (ICC’s) were calculated as outlined by Hopkins (2000). After
curve-fitting procedures were used to ascertain the linear relationships
between the data (SPSS v10.0, SPSS Inc.), validity statistics including
Pearson’s correlations and linear regression equations with standard error’s of
the estimates were calculated. For reliability and validity statistics, 95%
Confidence intervals (95% CI) were calculated for relevant data. Finally,
paired t-tests with Bonferroni correction were used to compare observed and
predicted (from regression equations) 1-RM test scores to examine
differences between data sets. Alpha was set at 0.1 to reduce the likelihood
of type II error (finding no difference between observed and predicted values
when a difference existed).
4.3 RESULTS
4.3.1 Reliability of ISQ and IFHS
Reliability statistics for ISQ and IFHS are presented in Table 4.1. For ISQ,
there was a small and non-significant increase in force produced in the
second testing session (26.9 N or 0.9% of 2321 N). The reliability of the test
was very high with ICC = 0.97 and typical error of only 69 N. For IFHS, there
94
was a small and non-significant decrease in the force produced in the
second testing session (26.9 N or 1.2% of 2335 N). The test-retest reliability
of the test was also very high with an ICC = 1.00 and typical error only 30 N.
Thus, the two isometric tests were very reliable.
FHS Mean LCI UCI Squat Mean LCI UCI
∆ mean (N) -21.0 -62.7 20.7 ∆ mean 26.9 -42.0 95.9
Typical Error 29.9 21.5 49.4 Typical Error 68.7 48.7 116.7
Peason’s r 0.99 Peason’s r 0.97
ICC 1.0 0.99 1.0 ICC 0.97 0.91 0.99
4.3.2 Validity of isometric measures
There was a significant relationship between the average ISQ (average of
testing week one and testing week two) and 1-RM squat performance, and
average IFHS and 1-RM FHS performance (see Table 4.2). There was
however a poor correlation between subject performances in ISQ and IFHS
tests and only a moderate correlation between 1-RM squat and FHS test
performances. Therefore subjects who performed well in the isometric tests
also performed well in the dynamic tests but subjects who performed well in
the squat tests did not necessarily perform well in the FHS tests.
Table 4.1. Reliability statistics for ISQ and IFHS. Both tests show high reliability. ∆ mean –change in the mean from test week 1 to test week 2, ICC – Intraclass Correlation Coefficient,LCI – lower limit of confidence interval (95%), UCI – upper limit of confidence interval (95%).
Table 4.2. Pearson’s correlations for test performances. Thesquat lift was highly correlated with the ISQ. FHS was highlycorrelated with the IFHS. Lower correlations were foundbetween squat and FHS.
95
Test comparisons r R2 p-value
ISQ versus squat 0.77 0.61 <0.01
IFHS versus FHS 0.76 0.59 <0.01
ISQ versus IFHS 0.47 0.23 >0.1
Squat versus FHS 0.55 0.30 >0.05
Force produced during isometric contractions was converted to weight in
kilograms and compared to individual’s 1-RM lifts. On average, ISQ lifts were
147% of those on the 1-RM and IFHS lifts were only 89% of the 1-RM. Linear
regression equations to predict 1-RM performance from isometric
performance are presented in Figure 4.2. The standard error of the estimate
for ISQ was 13.8 kg (95% CI = 10.9 – 18.6 kg) and for IFHS was 19.4 kg
(95% CI = 15.4 – 26.2 kg). These standard errors represent 8.5% and 7.3%
of the average performance in 1-RM squat and FHS respectively. There was
no significant difference between predicted and obtained values for the data
presented here.
96
4.4 DISCUSSION
4.4.1 Reliability and validity
The results of the present study suggest that the reliability of both the
isometric squat (ISQ) and isometric forward hack squat (IFHS) tests are very
high (ICC = 0.97 & 1.00 respectively). These intra-class correlation
y = 0.0432x + 163.85
R2 = 0.5747
0
100
200
300
400
0 1000 2000 3000 4000
Average Isometric FHS (N)
1-R
M F
HS
(kg
)
y = 0.0356x + 78.67
R2 = 0.5856
0
100
200
300
400
0 1000 2000 3000 4000
Average Isometric Squat (N)
1-R
M S
qu
at (
kg)
Figure 4.2. Scatterplots of isometric versus 1-RM test performance. The linear regressionequations and R2 values are indicated on the graphs. Almost 60% of the variation in 1-RMperformance can be accounted for by isometric test scores.
97
coefficients are similar to those previously reported for isometric (0.85 –
0.99 [Agre et al., 1987; Bemben et al., 1992; Viitasalo et al., 1981; Wilson et
al., 1993]) and 1-RM tests (0.92 – 0.98 [Henessey & Watson, 1994; Hoeger et
al., 1990; Hortobágyi et al., 1989; Sale, 1991]). The difference in mean
performance (shift in the mean) between repeated test occasions was less
than 1.5% of the average performance. For the subjects tested here
therefore, there was little or no difference between performances at each
testing occasion despite the complex multi-joint coordination required to
perform the present tests. This suggests that the isometric tests used in the
present study would be able to detect small changes in isometric strength
between subjects or after some form of intervention.
There was also a strong relationship between subject scores in the isometric
tests and the associated 1-RM tests (rsquat = 0.77, rFHS = 0.76; p<0.01) with
over 60% of the variation in 1-RM tests explained by subject’s isometric
performances. Thus, subject scores in the isometric tests were strongly
related to their 1-RM scores. Furthermore, there was no significant difference
between values predicted by regression equations and those obtained by
testing of subjects’ 1-RM. Isometric measures could then be considered good
indicators of dynamic performance.
Nonetheless, the correlations obtained here were less than 0.8 and could not
be considered indicative of high validity. R2 values for the correlations
between isometric and 1-RM tests suggest that up to 40% of the variance in
1-RM performance could be explained by factors other than isometric
performance (see Table 4.2). Furthermore, while the standard errors of the
estimates for the relationships between the isometric and 1-RM tests were
small (SEEsquat = 13.8 kg, SEEFHS = 19.4 kg), they still represent 8.5% and
7.3% of the average 1-RM score for the squat and FHS respectively. Thus
there is some error in predicting 1-RM performance from isometric
performance using the tests presented here. While performance in the
isometric tests could be used as a good indication of a subject’s 1-RM
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performance, and this performance could be predicted well from the
regression equations, precise estimates of 1-RM performance were not
possible.
4.4.2 Movement specificity
Of importance also is the weak relationship between subjects’ performances
in the squat and FHS tests. Those subjects who performed well in the squat
tests did not necessarily perform well in the FHS tests (risometric = 0.47, r1-RM =
0.55). Given the tests involve the same contraction modes (either isometric
[isometric tests] or an eccentric phase followed immediately by a concentric
phase [1-RM tests]), differences between test performances could be
attributed to their different movement patterns. The principle of movement
specificity has been shown extensively by past research (Abernethy &
Jürimäe, 1996; Baker et al., 1994; Blazevich & Gill, 2001; Blazevich et al.,
2000; Morrissey et al., 1995; Wilson et al., 1996). In the present study, high
force production in one posture was not always complemented by high force
production in the alternative posture suggesting an effect of movement pattern
on test performance.
4.4.3 Practical applications
The isometric squat and FHS tests were highly reliable and a strong
relationship existed between isometric and 1-RM performance. The ISQ and
IFHS tests could therefore be used to assess dynamic strength changes with
training. Given their high reliability, they could certainly be used to examine
changes in isometric strength between subjects, or after intervention.
However, the validity of the tests was moderate (r<0.8) and the number of
subjects tested here reasonably small. Caution should then be exercised
when trying to predict a subject’s precise 1-RM from isometric measures.
Furthermore, if the isometric tests were to be used to estimate changes in 1-
99
RM strength following intervention, the number of subjects would have to
be larger than if a 1-RM test was used. The increase in subject number would
equal 1/R2 (Hopkins, 2000), which for the ISQ test is 1/0.59, or 1.7, times the
subject number. Increasing subject numbers would increase the power of the
tests to nullify the loss of power caused by the moderate relationship between
the test types (lower validity of the isometric measures). Finally, subjects who
produced high forces in one posture (e.g. squat) did not necessarily produce
high forces in the other posture (e.g. FHS). Therefore, to best detect
performance changes with training, or differences between subjects, that test
which best matches the training movement patterns should be used.
4.4.4 Future research
Given the moderate validity of the isometric tests for estimating 1-RM
performance, some modifications could be made to the tests to improve their
validity. One change might be to vary the joint angles at which the test is
performed. In the present study, joint angles were chosen such that muscle
lengths were long and the forces relatively low. However, Sale (1991)
suggested that test variability was reduced when measurements were taken
at the strongest point in the range of motion. Moreover, Murphy et al. (1995)
found that the elbow angle in a bench press-specific isometric test affected
the relationship between isometric and 1-RM strength. The authors indicated
that tests should be performed at the joint angle at which peak forces were
provided. Thus, changing the joint angles adopted for the present isometric
tests may improve their validity.
Future research should also examine the relationship between these isometric
tests and their associated 1-RM tests by investigating the relationship
between changes in isometric and 1-RM strength after a period of resistance
training. While a highly reliable and valid isometric test should measure
performance similarly to its comparable dynamic test, this is not always the
case. Baker et al. (1994) found that a 27% improvement in 1-RM squat and
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9% improvement in isometric leg extension force after squat training were
unrelated (r = 0.16, p>0.05). This was despite significant correlations (r =
0.57 – 0.61) between the variables pre- and post-training which would have
indicated moderate validity. Such results are possibly due to the different
contraction modes between training and testing exercises. Nonetheless, the
low relationship between changes in the isometric and dynamic tests may be
related to their different movement pattern. The movement patterns of the
isometric tests used in the present study were similar to their 1-RM
counterparts, thus minimizing the differences between tests. However, it is
still unclear whether changes in ISQ and IFHS test performance would be
related to 1-RM squat and FHS test performance after a period of resistance
training.
4.4.5 Conclusion
The isometric squat and forward hack squat tests were highly reliable (>0.97)
and would therefore be able to detect small differences in multi-joint isometric
strength between subjects, or performance changes over time. They are well
related to their 1-RM counterparts (SQ and FHS) with significant correlations
found between the test pairs (p<0.01). However, validity correlations were
only moderate (rsquat = 0.77, rFHS = 0.76). Therefore it is unclear whether
these tests can discriminate small changes in dynamic strength. Although 1-
RM strength can be estimated well from the regression equations, precise
estimates of 1-RM strength were not possible. Future research should
examine the relationship between changes in 1-RM and isometric
performance after a period of training to determine whether movement-
specific isometric exercises such as those presented here can be used to
detect small changes in dynamic performance.
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RELIABILITY OF UNILATERAL AND
BILATERAL FORWARD HACK SQUAT TESTS
5.1 INTRODUCTION
Much research has investigated differences in force production between uni-
and bilateral movements. For example, Secher et al. (1976, 1978) reported
that maximal, voluntary, isometric strength of the leg extensors was greater
(115% and 123% for 1976 and 1978 studies respectively) under bilateral
conditions. More recently, Häkkinen et al. (1996) and Tanaguchi (1997)
showed that bilateral strength increased more in subjects who trained
bilaterally while unilateral strength improved most in subjects who trained
unilaterally. These specific changes appeared similar for different exercise
tasks (hand grip strength, leg extensor power and arm extensor power;
Tanaguchi, 1997). Such evidence has lead researchers to suggest that
adaptations to uni- and bilateral training are dissimilar. Also, the maximum
voluntary force that can be produced by a limb depends on whether a
unilateral or bilateral task is used in testing.
Given the laterality specificity of performance, testing of performance changes
after bilateral training should probably be done using bilateral tests. Also,
unilateral changes should be assessed by unilateral tests. However, while
bilateral testing protocols are common, and reliability and validity studies have
supported their use as testing tools (e.g. Arnold & Perrin, 1993; Rahmani et
al., 2000; Steiner et al., 1993; Wilhite et al., 1992), it is unclear if unilateral
tests show the same reliability. Unilateral pushing tasks are less commonly
performed and balance during unilateral tasks may be more difficult to
maintain. The reliability of unilateral tasks could therefore be lower than
bilateral tasks.
103
To the author’s knowledge, no research has compared the reliability of
unilateral and bilateral tests. Inspection of research that has included both
unilateral and bilateral testing has either shown that variability of
performances were similar between the two types of tasks (Häkkinen et al.,
1996; Howard & Enoka, 1991) or that perhaps bilateral tasks showed more
variability (Tanaguchi, 1997). Furthermore, variability of jump height, work,
joint torque and joint power values appeared similar for one- and two-legged
jumps (Van Soest et al., 1985). Thus, while no research has specifically
tested the hypothesis, it appears likely that uni- and bilateral tests of
performance would be equally reliable.
The purpose of the present study was to examine the reliability of test
performances in the dynamic forward hack squat task. The forward hack
squat was chosen as the test exercise since no reliability studies have been
performed for dynamic contractions and, given its novelty, subjects would be
unlikely to be accustomed to its movement pattern. While the reliability of
isometric FHS has been previously shown (Study Two), the reliability of
dynamic squats has not. As an adjunct, reliability will be measured with two
different loads placed on the machine to determine whether the load lifted (or
the velocity of the movement) affects the test’s reliability.
5.2 METHODS
5.2.1 Subjects
Eleven active, male subjects volunteered for the study (Age = 20.5 ± 1.1 yrs).
Subjects signed statements of Informed Consent and were free to discontinue
the study at any time. The research was approved by the Southern Cross
University Human Research Ethics Committee prior to the commencement of
testing.
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5.2.2 Protocol
Subjects participated in two identical testing sessions separated by one week.
In each session, testing was preceded by a five minute cycle at a self-
selected workload and two sets of two-legged forward hack squats with a self-
selected weight (equal to approximately 50% and 100% of bodyweight).
Cycle workload and weight lifted in the forward hack squat were recorded for
the first session and repeated in the second session.
5.2.3 Determination of testing loads
After warm-up, subjects performed two maximal, bilateral isometric
contractions lasting three seconds with hip and knee angles of 90o and 100o
(internal angle) followed by two unilateral contractions using the subjects’
preferred legs. The rails of the forward hack squat machine were aligned at
49o to the horizontal. Bilateral contractions were always performed before
unilateral contractions. Force produced by the subjects during the isometric
contractions was measured by a load cell placed in series with the movement
direction of the weighted sled (Output = 1.9231 mV/V, hysteresis <0.02%,
Model LPS-2KG, Scale Components Pty. Ltd., Australia). Force was sampled
at 100 Hz and the data fed into a personal computer (IBM compatible 486 DX)
and stored using a custom program written using AMLAB software
(Chatanooga, Inc., USA).
Weights equal to 40 and 70% of maximum isometric force were then
calculated using the following equation:
Weight = x * (y/100) - 74.6 kg
cos 41o / 9.81
where y is the percent required of the isometric maximum (equal to 40 or 70),
105
x is isometric maximum force in Newtons, cos 41o is used to calculate the
vertical component of the total isometric force, 9.81 (m.s-1) is a gravity
constant that is used to convert Newtons (N) to kilograms, and 74.6 kg is the
vertical component of the weight of the sled apparatus which forms part of the
total weight of the lifted system. The kilogram amount was then added to the
sled to the nearest five kilograms and maximal dynamic contractions
performed.
5.2.4 Test contractions
Subjects performed two maximal, dynamic contractions at both the 40% and
70% loads (i.e. two one-legged trials at both 40% and 70%, and two two-
legged at both 40% and 70%). The order of contractions was randomised
between subjects to minimise order effects. The weight was lowered in a
controlled eccentric phase lasting one to two seconds and then raised as
rapidly as possible. A spring mechanism prevented the sled from moving out
of the subject's reach at the top of the movement and allowed a safe, maximal
push to the limit of the subject's range of motion. Subjects were asked to hit
the spring at the top of the movement as hard as possible. All subjects were
allowed several familiarisation trials to gain confidence in the spring
mechanism prior to the recorded trials. Thus there was no deceleration of the
weight prior to hitting the spring. One minute of rest was allowed between
trials of a lift and five minutes of rest was allowed between different types of
lift. During dynamic trials, the force transducer again recorded force.
5.2.5 Data analysis
Reliability statistics including the difference in the mean force between the two
trials and the intra-class correlation coefficients were calculated by the
methods of Hopkins (2000). 95% confidence intervals (CI) were also
calculated to show the variation in reliability statistics. Finally, the bilateral
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deficit was calculated similarly to that proposed by Howard & Enoka (1991)
except that instead of forces produced in left leg and right leg trials being
added and compared to the bilateral condition, the force produced in the
single leg condition was doubled. This would cause slight overestimation of
the bilateral deficit since often one leg is stronger than the other is and, in
general, subjects would have performed the trials with their strongest leg.
5.3 RESULTS
Mean (± SD) force production for the four conditions is presented in Table 5.1.
More force was produced during trials at the 70% load than at 40%.
Furthermore, more force was produced during bilateral trials. Interestingly,
force produced in the bilateral trials was less than double the force produced
during the unilateral trials. The subjects therefore exhibited a bilateral deficit
(-26.9% at 40% load, -28.2% at 70% load).
Testing
occasion
Trial Mean Force (N) SD (N)
First session 1L 40% 1176 2731L 70% 1721 2332L 40% 1706 2172L 70% 2540 379
Second session 1L 40% 1156 1481L 70% 1776 2892L 40% 1704 2432L 70% 2481 356
Results of the reliability tests are presented in Table 5.2. Intra-class
correlation coefficients were higher for trials at the 70% load than 40%. The
variability of the coefficients (indicated by the 95% CI) was also less for the
70% load. Therefore, reliability of trials at the heavier load was greater than
Table 5.1. Mean (±SD) force produced during each trial. More forcewas produced in trials at the 70% load and during bilateral trials.
1L – one-legged (unilateral), 2L – two-legged (bilateral)40% - 40% of isometric maximum added to machine70% - 70% of isometric maximum added to machine
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for the lighter load. There appeared to be no effect of laterality on task
reliability.
Trial ICC 95% CI Change inMean (N)
95% CI
1L 40% 0.70 0.13 – 0.92 33.6 32.5 – 99.71L 70% 0.90 0.66 – 0.97 55.8 -222.0 – 133.62L 40% 0.64 0.06 – 0.89 70.7 -75.9 – 217.42L 70% 0.95 0.72 – 0.99 -17.1 -119.7 – 85.5
5.4 DISCUSSION
The purpose of the present study was to examine the reliability of test
performances in the dynamic forward hack squat task. The forward hack
squat was chosen as the test exercise since no reliability studies have been
performed for dynamic contractions and, given its novelty, subjects would be
unlikely to be accustomed to its movement pattern. As an adjunct, reliability
was measured with two different loads placed on the machine to determine
whether the load lifted (or the velocity of the movement) affected the test’s
reliability. Results of the reliability tests suggest that there was no difference
in the reliability of unilateral and bilateral tests. The result is interesting given
that unilateral strength tasks are less commonly performed and balance
during unilateral tasks may be more difficult to maintain. One could consider
that complex motor tasks that are performed unilaterally would be more
difficult to learn than bilateral tasks. However the results of the present study
suggest that subjects were equally able to perform uni- and bilateral tasks
reliably.
Of interest was the finding that the reliability of tasks at the heavier (70%) load
was higher than tasks at the lighter (40%) load. The result suggests that
Table 5.2. Reliability statistics for force produced during dynamicforward hack squat trials. Reliability was greater for the heavier loadswith no difference between uni- and bilateral trials.
1L – one-legged (unilateral), 2L – two-legged (bilateral)40% - 40% of isometric maximum added to machine70% - 70% of isometric maximum added to machine
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something related to either the load lifted, or velocity of the movement,
affected reliability. The most likely explanation for this result is that the
greater load promotes greater kinaesthetic feedback from muscle, tendon and
joint proprioceptors. Particularly, muscle spindles, golgi tendon organs and
pacinian corpuscles could provide more feedback under the heavier loads.
Stretch or pressure stimulates proprioceptors. The greater the stretch or
pressure, the greater the feedback from these receptors. This information is
then received by the spinocerebellum which compares the information to the
signals sent from the cortical motor area (Sherwood, 1993). The
spinocerebellum then corrects deviations from the intended movement. Thus,
greater loads would allow more information from proprioceptors for the
spinocerebellum to correct movement.
Of final note is the result that the force produced during bilateral trials was
less than twice that produced in the unilateral trials. Thus the subjects in the
present study exhibited a bilateral deficit as has been reported in previous
studies (Häkkinen et al., 1996; Howard & Enoka, 1991; Tanaguchi, 1997).
The bilateral deficit was calculated similarly to that proposed by Howard &
Enoka (1991) except that instead of forces produced in left leg and right leg
trials being added and compared to the bilateral condition, the force produced
in the single leg condition was doubled. This would cause slight
overestimation of the bilateral deficit since often one leg is stronger than the
other is and, in general, subjects would have performed the trials with their
strongest leg. Nonetheless, the result provides further evidence that unilateral
and bilateral tests measure different entities and that testing should be
specific with respect to laterality. For example, strength tests measuring
changes in performance after unilateral training should be performed
unilaterally. This is especially true in light of the findings of the present study
that suggest the reliability of complex, unilateral tasks is as high as bilateral
tasks.
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CCHHAAPPTTEERR 66:: SSTTUUDDYY FFOOUURR
110
PERFORMANCE RELATIONSHIPS
BETWEEN VERTICAL JUMP, SPRINT RUNNING
AND STRENGTH TRAINING EXERCISES:
IMPLICATIONS FOR MOVEMENT SPECIFICITY
6.1 INTRODUCTION
Based on the results of Study One it was concluded that the timing and
magnitude of hip, knee and ankle joint angle changes were similar for JSQ
and VJ (with arms crossed over the chest) tasks and for the FHS and the
acceleration phase of a sprint run. However, it is unclear whether subjects
who perform well in a JSQ or FHS test would also perform well in a VJ or
sprint run. The results of longitudinal studies indicate that adaptations to an
exercise stimulus are specific to the movement patterns of the training
exercises (Lindh, 1979; Martin et al., 1994; Rutherford et al., 1986; Thépaut-
Mathieu et al., 1988; Weir et al., 1994), even when the movement velocity of
the training exercise differs from the test exercise (Wilson et al., 1996; Young
& Bilby, 1993). As such, a subject could be expected to perform equally well
relative to other subjects in tests that require the same movement patterns,
even if the movement velocities of the tasks were dissimilar.
This creates somewhat of a paradox since the velocity specificity of
movement has also been extensively shown (Blazevich & Jenkins, 1997;
Caiozzo et al., 1981; Ewing et al., 1990). It is therefore unclear whether
adaptations to exercise are specific to the velocity of the training exercises, or
to some other closely related principle. It is possible that adaptations are
specific to the neuromuscular intent of the task rather than movement velocity
per se (Behm & Sale, 1993a). In the present thesis, the phrase
‘neuromuscular intent’ describes the ‘intended’ mode/s of muscular action.
111
That is, it describes the intention to provide concentric, eccentric or
isometric muscle contractions regardless of whether the muscles actually
lengthen or shorten and the actual mode and velocity of movement is not
considered. For example, the ‘neuromuscular intent’ during a VJ is to produce
high static muscle force, or to provide muscle stiffness in the squatting
position (transition between downward and upward phases), and then to
contract rapidly during the upward phase. Regardless, the entire movement
is regarded as high-velocity.
Examples of research indicating that neuromuscular intent, rather than
movement velocity, is an important factor in the adaptive process to
resistance training are limited. Adams et al. (1992) showed that a
combination of squat and plyometric training was superior to using only one
form of training to improve VJ performance. One could speculate that squat
training improved subject’s muscle strength and stiffness, while plyometric
training improved subject’s intermuscular coordination (Bobbert & Van Soest,
1994), use of the stretch-shorten cycle and high-velocity force production.
Therefore, training was optimum when exercises were specific to both
movement pattern and mode (neuromuscular intent). Further, Behm and
Sale (1993a) hypothesised that the ‘intent’ to perform rapid contractions was
important for velocity-specific adaptations to occur. Thus, while movement
pattern specificity is seen even with tasks of different velocities, the
neuromuscular intent of exercises might be important.
The purpose of this study therefore was to investigate the relationship
between subjects’ performances in JSQ and VJ tests, and the FHS and 20 m
sprint tests, to determine the extent to which subjectss performances in
certain tests were dependent on similarities in the movement pattern,
movement velocity and/or neuromuscular intent of the tests. It was
hypothesised that if movement pattern solely determined task similarity,
subjects would perform equally well (relative to other subjects) in JSQ and VJ
tests, and FHS and sprint tests. If both the movement pattern and
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neuromuscular intent were important then not only should subject
performances in dynamic FHS tests and sprint tests be similar but so should
subject performances in ISQ and VJ tests. The VJ requires high levels of
muscle force for optimum use of the stretch-shorten cycle prior to the upward,
concentric, phase (Asmussen & Bonde-Petersen, 1974; Gollhofer et al., 1992)
and would therefore largely require the same neuromuscular intent as an ISQ
performed in a squating position. Finally, if movement velocity was important,
better relationships might exist between JSQ, VJ and sprint than ISQ tests.
6.2 METHODS
6.2.1 Subjects
Thirty-one athletic subjects including 23 men and eight women volunteered
from the University population (age range = 18 - 26 yrs). All subjects were
currently participating in organised sport (minimum of club-level) and had a
minimum of six months of resistance training experience. Both male and
female subjects were included in the study on grounds of equity however all
subjects had to perform a 20 m sprint in under 4 s and produce at least 1800
N in an isometric squat (knee angle 90o). Subjects had no recent injury or
medical conditions that would impede maximal performance and all subjects
read and signed statements of informed consent prior to participation. The
project was approved by the Southern Cross University Human Research
Ethics Committee prior to the commencement of testing.
6.2.2 Procedure
Following a standardised warm-up including ten minutes of low-impact
aerobic activity involving walking, running, subjects performed SQ, FHS, VJ
and 20 m sprint tests. Two minutes rest was allowed between successive test
trials while ten minutes of rest was allowed between the performance of
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different tests. The order of tests was randomised between subjects by
each of the first 24 subjects being given one of 24 possible testing orders.
The next seven subjects were randomly allocated a testing order such that no
more than two subjects had the same test order. Thus the influence of
fatigue/potentiation on performance was minimised.
6.2.2.1 20 m sprint
Subjects’ times to run 10 m and 20 m were recorded by infra-red electronic
timing lights (Swift Performance Equipment, Australia) while running on a
synthetic, indoor surface. All subjects performed four practice runs at
increasing speed starting at a 'fast jog' and culminating in a maximal run.
Each subject was then allowed three timed runs, although a fourth run was
allowed if subjects produced their best time on the third run. Each sprint was
started from a semi-squatting position with one foot placed in front of the other
to lower the body's centre of mass and permit a more optimum acceleration
than that gained from an upright start. However 'crouch' starts of the type
seen in competitive running were not permitted to prevent bias toward
experienced sprint runners. The toe of the front foot was placed 30 cm
behind a line that marked the start of the 20 m. In this way the subjects’
forward lean did not prematurely break the infra-red beam between the
starting gates and activate the electronic timing mechanism. Subjects had
performed eight sprint sessions over four weeks prior to testing to practice
acceleration technique and ensure optimum running performance.
Subjects started in their own time with no external command. Timing was
automatically started when the subject broke the beam between the first pair
of timing lights (at 0 m of the 20 m). All subjects wore standard jogging shoes
and no performance shoes (i.e. spiked shoes) were allowed. Subjects were
instructed to run maximally to pass through all of the timing gates in the
minimum time.
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6.2.2.2 Vertical Jump
Force and displacement were recorded for three maximal, double-leg VJ’s
with the subject’s arms folded across their chests. All had performed eight VJ
training sessions over four weeks prior to testing to practice jump technique
and ensure reliable jump performance. A cable position transducer with a
plastic-hybrid precision potentiometer (Model PT9101, accuracy ±0.10% full
stroke, Celesco Transducer Products, Inc., USA) measured displacement.
The cable was connected to a belt tightly secured around the subject’s waist
(Figure 6.1).
Voltage from the position transducer was sampled at 100 Hz using a personal
computer (IBM compatible, 486 DX) and stored on disc. Subsequently,
displacement was calculated using a scaling factor by a custom program.
The data were then smoothed with a fourth-order, zero-lag Butterworth filter
with a cut-off frequency of 10 Hz. Force was recorded using a Kistler Force
Platform (Type 9287, Kistler Instrumenté, Switzerland). Force data were
sampled at 1000 Hz using a personal computer (IBM compatible 486DX).
From force and displacement data maximum force, displacement, velocity,
Cable to transducer (above, not shown).
Belt to which cable was secured.
Figure 6.1. Body position for VJ showingcable (to position transducer) and belt.
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Figure 6.2. Position for isometric squat test. Hipangles were measured during a squat with a freebar. Knee angles were maintained at 90o.Subjects then descended to these angles duringthe free-weight squat lifts.
power, time to peak power, and rate of power development were calculated
on all jumps.
6.2.2.3 Squat lift
Subjects performed three squat lift tasks: an ISQ and JSQ’s at 30% and 60%
of isometric maximum. Results from Study Two showed that these loads
were equal to approximately 44% and 88% of dynamic 1-RM. First, subjects
were asked to squat with an unloaded bar to a 90o knee angle and their hip
angle was measured. They then squatted under a bar that was fixed and
immovable such that their hip and knee angles were the same as those
recorded during the unloaded squat. This position is shown in Figure 6.2.
Subjects were instructed to perform a maximal isometric squat against the bar
for three seconds during which time force was measured by a Kistler Force
Platform, sampled at 1000 Hz and stored on computer. The instruction was to
perform the squat ‘as hard as possible’ and the maximum force recorded was
taken as isometric squat strength.
The peak in force was converted from Newtons of force to kilograms of weight
by dividing by the gravity constant of 9.81 ms-2 and 30% and 60% of this load
116
calculated. Subjects then performed three squats (with a free bar) on the
force platform with these loads. The subjects were required to lower the
weight slowly to a 90o knee angle (practice repetitions allowed the subjects to
estimate this position and each trial was observed to ensure the knee angle
was very close to 90o at the bottom of the movement). The subject then
exerted maximum effort upward against the weighted bar which was lifted
rapidly such that subjects’ feet often left the ground. The squat could be best
described as a jump squat (JSQ). The maximum force recorded during the
concentric (upward) phase was taken as a measure of squat strength
(Schmidtbleicher & Buehrle, 1987). The same test was repeated for the 60%
load. Thus, force measures were obtained for the squat lift under isometric
conditions, and with two different dynamic loads. From the force data, peak
force and time to peak force were calculated.
6.2.2.4 Forward Hack Squat
Subjects performed three maximum efforts of a two-legged FHS. These
included a maximal IFHS and lifts at 40% and 70% of isometric maximum.
Results from Study Two showed that these loads were equal to approximately
36% and 62% of dynamic 1-RM. The subject placed two feet on the foot
platform such that the body formed a straight line from the head to the ankle
while in the standing position. The subjects then lowered the weight until the
internal hip angle was 90o and the internal knee angle was 110o (Figure 6.3).
This approximated the hip and knee angles during push-off in the acceleration
phase of sprint running (Jacobs & Ingen Schenau, 1992). A metal peg was
used to hold the machine in this position for subsequent maximal isometric
contractions. For these contractions, subjects lifted the sled slowly until the
metal peg stopped its upward movement and hip and knee angles were
checked to ensure they were at 90o and 110o respectively. Subjects then
provided a maximal isometric contraction (i.e. as hard as possible) while
maintaining the pre-determined hip and knee angles. The contractions lasted
three seconds. Force during each isometric contraction was sampled at 100
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Figure 6.3. Position for the isometricforward hack squat (FHS). The hipangle (angle between the C7 vertebra,greater trochanter and lateral condyle)was 90o and knee angle 110o.
Hz by a load cell placed in series with the movement direction of the weighted
sled (Output = 1.9231 mV/V, hysteresis <0.02%, Model LPS-2KG, Scale
Components Pty. Ltd., Australia). The signal was collected using a personal
computer (IBM compatible 486 DX) and data stored using a custom program
written using AMLAB software (Chatanooga, Inc., USA; see Appendix X).
To determine weights equal to 40% and 70% of maximum isometric force, the
vertical component of the force was calculated first. The following equation
was used:
Weight = x * (y/100) - 74.6 kg
cos 41o / 9.81
where y was the percent required of the isometric maximum (equal to 40 or
70), x was the previously determined isometric maximum force in Newtons,
cos 41o was used to calculate the vertical component of the total isometric
force, 9.81 (m.s-2) is the gravity constant used to convert Newtons (N) to
kilograms, and 74.6 kg is the vertical component of the weight of the sled
apparatus which forms part of the total weight of the lifted system. That is, the
vertical component of the total force provided during the isometric contraction
was calculated, a percentage of that weight determined (40% or 70%) then
the weight of the sled was subtracted to determine the actual weight to be
added to the sled. The kilogram amount was then placed on the sled to the
nearest five kilograms.
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Subsequently, the subject performed maximal, dynamic contractions at the
40% and 70% loads where the weight was lowered in a controlled eccentric
phase lasting one to two seconds and then raised as rapidly as possible. A
spring mechanism prevented the sled from moving out of the subject's reach
at the top of the movement and allowed a safe, maximal push to the limit of
the subject's range of motion. The subject was asked to hit the spring at the
top of the movement as hard as possible. All subjects were allowed several
familiarisation trials to gain confidence in the spring mechanism prior to the
recorded trials. Thus there was no deceleration of the weight prior to hitting
the spring. During dynamic trials, both force and displacement were
recorded. Displacement was measured by a cable position transducer (as
described previously) with the cable attached to the sled apparatus and data
was collected using an IBM compatible computer. From the force and
displacement recordings, maximum movement velocity, peak force and peak
power were calculated as measures of performance.
6.2.3 Data Analysis
After force and displacement data were collected during the SQ, FHS and VJ
tests, various performance variables were calculated, as mentioned above, by
a custom program. All variables were subject to Correlation and Components
Analysis (SPSS for Windows v10.0, SPSS Inc.). Numerous variables (related
to power, maximum movement velocity and time to peak force and power)
were highly inter-correlated and were listed under the same components in
the Component analysis. Such variables were eliminated from further
analysis since they provided no information in addition to that gained from
analysing displacement and force variables (from which they were calculated)
alone. As such, analysis of the results was limited to force measures for the
resistance tasks, as well as VJ height and sprint running time.
Pearson's product moment correlation coefficients were calculated to
119
determine relationships among the performance variables. Alpha level was
set at 0.01 to decrease the likelihood of Type I error. Thus only highly
significant relationships were reported as such. The various components
associated with subject performances were also analysed by Components
Analysis using Principal Components extraction and Varimax rotation (SPSS
for Windows v10.0, SPSS Inc.).
6.3 RESULTS
Descriptive statistics for the variables analysed are presented in Table 6.1.
Results of the correlation analysis are presented in Table 6.2. Two-legged
FHS performance was significantly correlated with 10 m and 20 m sprint time
(r = -0.54 – -0.73, r2 = 0.29 – 0.53; p<0.01) such that subjects who ran faster
also performed better in FHS tests. Force produced during the SQ was also
correlated with 10m and 20 sprint time although the correlations were
consistently, but only slightly, lower (r = -0.51 – -0.67, r2 = 0.26 – 0.45; p<0.01;
compare correlations in Table 6.2). Indeed coefficients of determination
suggest that the proportion of the sprint times that can be accounted for by
squat performance was less than 45%. Force produced during the FHS
(isometric, 30% and 60%) were also significantly related to VJ height (r = 0.53
Table 6.1. Mean performance (±SD) forthose variables selected for analysis.
Performance Variable Mean (±SD)10 m sprint time (s) 1.89 (0.22)20 m sprint time (s) 3.28 (0.40)VJ height (m) 0.42 (0.10)FHS isom. (N) 1824 (487)FHS force 40% (N) 1182 (473)FHS force 70% (N) 2004 (586)Squat force isom. (N) 1709 (305)Squat force 30% (N) 1915 (397)Squat force 60% (N) 2294 (586)isom. – isometric30%, 40%, 60%, 70% - load lifted aspercent of isometric maximum.FHS – forward hack squat test
120
– 0.71, r2 = 0.28 – 0.50; p<0.01) as was force produced during ISQ (r = 0.63,
r2 = 0.40; p<0.01) and squat with a load of 30% of isometric maximum (r =
0.55; r2 = 0.30; p<0.01). However force produced during a squat with 60% of
isometric maximum was not significantly correlated (Figure 6.4).
Table 6.2. Significant correlation coefficients (p<0.01) forperformance data.
Strength Variable 10 m time 20 m time Vertical jump
FHS isom. -0.72 -0.73 0.56
FHS force 40% -0.54 -0.56 0.58
FHS force 70% -0.72 -0.71 0.68
Squat isom. -0.67 -0.51 0.63
Squat force 30% -0.50 -0.61 0.55
Squat force 60% -0.61 -0.67 (0.44)
isom. – isometric30%, 40%, 60%, 70% - load lifted as percent of isometric maximum.FHS – forward hack squat testAll correlations (non-bracketed) are significant, p<0.01.Bracketed correlation coefficients were not statistically significant.
0500
10001500200025003000350040004500
0 0.2 0.4 0.6 0.8
Vertical Jump Height (m)
Squ
at F
orce
(N
)
Squat forceisom.
Squat force60%
Linear (Squatforce 60%)
Linear (Squatforce isom.)
Figure 6.4. Scatterplots of isometric force produced during a squat (Squat force isom.)and force during a squat with a load of 60% of maximum isometric load (Squat force 60%)against VJ height. There is a higher correlation between ISQ force and jump height (r =0.63) than squat force at 60% of isometric maximum and jump height (r = 0.44).
121
Results of the Components Analysis were that the variables could be
grouped according to four components (see Table 6.3). The components in
Table 6.3 have been ordered according to the movement velocities and loads
of the movements with Component 1 being the slowest movement velocity
and Component 2 the fastest. SQ and IFHS variables have not been grouped
with any of the high-speed movements suggesting that their force-velocity
characteristics were different. The results also show however that sprint time
was not grouped with any of the FHS variables despite subjects performing
well in the FHS also performing well in the sprint (i.e. they were highly
correlated).
Another interesting finding of the study was that there was a plateau in sprint
running performance at high strength levels. That is, sprint times did not
improve linearly with strength at the highest strength levels (Figure 6.5). This
would have reduced the correlation between FHS and sprint performances
and suggests that strength is not the most important factor in performance in
fast runners.
Table 6.3. Results of the Factor Analysis. The analysis has revealed four componentsthat could be related to the movement velocity (or load) of the test. Components arearranged according to their movement velocity (i.e. 1,3,4,2).
Component 1 3 4 2
Variables Squat isom.Squat force 30%Squat force 60%FHS isom.
FHS 70% FHS 40% 10 m time20 m timeVJ height
Movement velocity
Movementload
Very low
Very high
Low
High
Moderate
Moderate
High
Moderate83% of total variance can be explained by the four components.Minimum communality = 0.65.isom. – isometric force30%, 40%, 60%, 70% - load lifted as percent of isometric maximum.FHS – forward hack squat test
122
6.4 DISCUSSION
Correlations between dynamic squat (which could be considered jump squats
since subjects’ feet invariably left the ground during the ascending phase) and
VJ performance were generally poor with the highest correlation being
between the ISQ and VJ (r = 0.63; p<0.01). Results of the component
analysis indicate also that their force-velocity characteristics were different
(Table 6.3). Therefore, although the results of Study One were that subjects
adopted similar movement patterns during the performance of VJ and JSQ
exercises, they were not well related functionally (r = 0.55; r2 = 0.3). A likely
reason for this discrepancy would be the different movement velocities
achieved and load lifted during performance of the tasks. The VJ is
performed at a high velocity and utilises the stretch-shorten cycle whereas the
squat lift is performed slower and with heavier loads. Indeed the lightest
dynamic squat was performed with a load equal to 30% of isometric maximum
(approximately 44% of dynamic 1-RM; Study Two). These loads are far
greater than for the VJ and the movement velocities achieved were therefore
0
500
1000
1500
2000
2500
3000
2.5 3 3.5 4 4.5
20 m Sprint Time (s)
FH
S F
orce
(N
)FHS isom.
FHS force 40%
Figure 6.5. Scatterplots of isometric force produced during a forward hack squat (FHSisom.) and force during a FHS with a load of 40% of maximum isometric load (FHS force40%) against 20 m sprint time. There is a plateau in sprint times at around 2.7 s.
123
very different. Thus, movement pattern alone did not determine task
similarity.
There was however a significant correlation between ISQ force and VJ height
despite the contraction modes of the two tasks being different. The close
performance relationship might reflect the necessity for high muscle strength
(muscle stiffness) in the squatting position for performance of both tasks (i.e.
the intent to produce high muscle stiffness regardless of the actual mode of
contraction; neuromuscular intent). The countermovement jump relies largely
on the stretch-shorten cycle for power development (Gollhofer et al., 1992).
Pre-activation of muscles to attain high muscle forces has been shown to
enhance the storage and utilisation of elastic energy in stretch-shorten
movements (Asmussen & Bonde-Petersen, 1974; Gollhofer et al., 1992) thus
increasing their efficiency. Further, earlier activation of agonist muscles in a
movement allows more work to be done early in that movement (Bobbert et
al., 1996; Fukashiro et al., 1995; Voigt et al., 1995; Walshe et al., 1997;
Wilson et al., 1991). The ability to use the stretch-shorten cycle optimally in
vertical jumping is therefore contingent on being able to attain high levels of
muscle force/stiffness in the squatting position. Given the high correlation
between ISQ force and VJ height, it appears that task similarity depended on
both the movement pattern and intent to produce high muscle force/stiffness.
Correlations between isometric and dynamic FHS force and sprint running
time were generally high (r = 0.56 – 0.73; p<0.01). Therefore, subjects who
produced large forces in the FHS tests also performed well in the sprint test.
The plateau in 20 m sprint times at high FHS forces (Figure 6.4) would have
affected this correlation. Component analysis revealed that performances in
FHS and sprint tasks were described by different components. 10 m and 20
m sprint times were listed under component 2, generally representing high
velocity movements (see Table 6.3), whereas the dynamic FHS variables (i.e.
not the isometric variables) were listed under components 3 and 4, generally
representing moderate or slower-velocity movements. A conclusion that may
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be drawn from this is that while the sprint and FHS tests could not be
considered identical (given their different movement velocities), the similarity
in their movement patterns and force-velocity requirements were not as
different as for the isometric and dynamic squat and sprint/vertical jump tasks.
Since the weights used in FHS relative to 1-RM (36% and 62%) were lower
than for the squat (44% and 88%), the result was somewhat expected. Given
the movement patterns are the same (see Study One) and subjects who
performed well in FHS tests also performed well in the sprint tests, it appears
that movement specificity is determined both by the movement pattern and
neuromuscular intent, but not the velocity, of the tasks.
The results of this study offer some insight to the complex functioning of the
neuromuscular system. From Study One it was concluded that the movement
patterns of the JSQ and FHS exercises were similar to the VJ and sprint
(acceleration phase) respectively. Movement pattern-specific adaptations to
training have been shown repeatedly (Martin et al., 1994; Rutherford & Jones,
1986; Thépaut-Mathieu et al., 1988; Weir et al., 1994; Wilson et al., 1996),
even when training and testing exercises were performed at different
contraction velocities (Wilson et al., 1996; Young & Bilby, 1993). The results
of such research suggest that subjects should perform well in tests with the
same movement patterns. One would therefore conclude that, to at least
some degree, subjects who performed well in one resistance exercise would
also perform well in its related performance task. However, in this study,
subjects who performed well in the JSQ tests did not necessarily perform to
the same relative level in the VJ test.
These results may have been due to the resistance and performance (VJ and
sprint) tasks having different force-velocity characteristics (different
neuromuscular intent). The squat tests possibly required high dynamic
muscle strength while performance in the VJ tests depended on the efficiency
of the stretch-shorten cycle. The ISQ and VJ tests may have been more
functionally similar because of the high muscle force/stiffness required for
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their performance (same neuromuscular intent). The results of this study
also suggest that while there was some difference in the force-velocity
characteristics of the FHS and sprint tests, neuromuscular intent was the
same. Therefore, subjects were likely to produce comparable performances
in tasks that had similar movement patterns, and required similar
neuromuscular intent. The velocity of movement was not a major factor. The
next step toward understanding the effect of movement pattern, movement
velocity and neuromuscular intent on training adaptations is to perform
longitudinal research investigating adaptations to the different types of
training.
In summary, specificity of task performance in humans has previously been
shown to be related to the movement pattern of tasks even when the
velocities at which the tasks were performed were not the same (Wilson et al.,
1996; Young & Bilby, 1993). However, the results of this study suggest that
the neuromuscular intent of the tasks is also important. The results do not
indicate that the actual movement velocity of exercises is important since ISQ
force was well related to VJ performance. A longitudinal study would best test
the influence of movement pattern and neuromuscular intent on training
adaptations.
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CCHHAAPPTTEERR 77 –– SSTTUUDDYY FFIIVVEE
127
NEUROMUSCULAR AND PERFORMANCE
ADAPTATIONS TO SHORT-TERM CONCURRENT
RESISTANCE AND SPRINT/JUMP TRAINING
7.1 INTRODUCTION
Adaptations to RT appear specific to the movement patterns (Abernethy &
Jürimäe, 1996; Kitai & Sale, 1989; Weir et al., 1994; Wilson et al., 1996) and
velocities (Caiozzo et al., 1981; Delecluse et al., 1995) of the exercises used
in training. In studies investigating the movement-specific adaptations to
training, much of the specific adaptations have been ascribed to changes in
muscle recruitment strategies (Kitai & Sale, 1989; Weir et al., 1994) or in the
length-force characteristics of sarcomeres (Herring et al., 1984; Koh, 1995;
Van Eijden & Raadsheer, 1992). Velocity-specific adaptations have been
ascribed mostly to increases in type-II myosin heavy chain isoforms within
sarcomeres (Adams et al., 1993; Andersen et al., 1994), increases in the total
size or number of type II muscle fibres (Jansson et al., 1990; Mannion et al.,
1993) or an increase in the recruitment of motor units during muscle
contraction (Behm & Sale, 1993b; Cannon & Cafarelli, 1987; Häkkinen et al.,
1985 a,b; Häkkinen & Komi, 1985, 1986). Thus, specific adaptations to RT
occur in many different parts of the neuromuscular system. Despite this, little
research has examined movement-specific changes in muscle architecture, or
examined both muscular and neural changes simultaneously. Furthermore
longitudinal studies investigating movement pattern-specific effects have been
fraught with limitations (this will be discussed later).
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7.1.1 Muscle Architecture
Muscle architecture describes the size of a muscle in terms of the volume,
cross-sectional area or thickness, the angulation of its fibres relative to the
tendon [pennation) and the length of its fibres (measured as fascicle length)
after training. These factors have been shown to change with RT
(Henriksson-Larsén et al., 1992) however little research has investigated such
changes. With respect to muscle size, increases have been commonly
observed after periods of resistance-type training with much of this increase
being related to fibre size (Colliander & Tesch, 1990; Narici & Kayser, 1995;
Sale et al., 1992; Wang et al., 1993). Increases in muscle size in response to
training appear after several weeks (Moritani, 1993; Moritani & DeVries, 1979;
Narici et al., 1989) and certainly after changes have occurred at the
sarcomere (Heslinga et al., 1995; Williams, 1990) and in the nervous system
(DeVries, 1968; Narici et al., 1989; Sale, 1988). Since few changes have
been seen in the electromyogram of experienced weight trainers (Häkkinen et
al., 1987, 1991), increases in muscle size have been proposed as the major
determinant of muscle strength in well-trained athletes (Narici et al., 1989).
In addition to muscle size changes, changes in muscle pennation could affect
strength development. Increases in pennation possibly allow a greater
muscle mass to attach to a given area of tendon (Kawakami, 1993; Rutherford
& Jones, 1992). As such pennation should increase with the size of the
muscle. Research examining the relationship between muscle size and
pennation (Henriksson-Larsén et al., 1992; Kawakami et al., 1993, 1995;
Rutherford & Jones, 1992) has not conclusively shown whether the two
variables are (Kawakami et al., 1993, 1995; Rutherford & Jones, 1992 [cross-
sectional]) or are not (Henriksson-Larsén et al. 1992; Rutherford & Jones,
1992 [longitudinal]) related. Therefore it is still unclear whether pennation
changes occur in response to changes in muscle size.
Longer muscle fibres have been theoretically and experimentally shown to
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contract at higher velocities than shorter fibres (Burkholder et al., 1994;
Sacks & Roy, 1982; Wickiewicz et al., 1984). Since fibres are grouped into
fascicles, and the spaces between fascicles are visible in vivo using
ultrasound and computer aided techniques, fibre length is commonly
estimated by measuring the length of these fascicles (Fukunaga et al., 1997;
Kawakami et al., 1998). However no research had examined the relationship
between fascicle (fibre) length and human movement performance until Abe
et al. (1999) showed that fascicle length was greater in sprinters than long
distance runners, and Kumagai et al. (2000) showed a significant relationship
between fascicle length and sprint performance in 100 m sprinters. Still no
research has investigated changes in fascicle length (fibre length) in
controlled training studies using concurrent resistance and task training.
Therefore it is unclear whether fascicle length is altered in response to RT, or
concurrent resistance and task training.
7.1.2 Longitudinal Research
While some longitudinal studies have investigated neuromuscular changes
accompanying training, the exact neuromuscular adaptations that result from
training, and the populations to which the results can be related, are still
unclear. First, subjects in most training studies are not well-trained and
adaptations within their neuromuscular system may well be different to trained
individuals (Häkkinen et al., 1987; Narici et al., 1989). Second, the subjects in
such training studies have generally trained using isokinetic (Ewing et al.,
1990; Mannion et al., 1994; Narici et al., 1989) or isotonic (Abernethy &
Jürimäe, 1996; Petersen et al., 1989; Sale et al., 1992; Wilson et al., 1993,
1996) training modes without also performing additional, task-specific,
practice. A paucity of research has examined the effect of training movement
pattern or velocity when subjects performed both resistance- and task training
concurrently (Delecluse et al., 1995; Tanaka et al., 1993; Voigt & Klausen,
1990). Research that has examined adaptations to concurrent training
suggests that RT performed at high velocities (Delecluse et al., 1995) may be
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more beneficial than that at lower velocities (Tanaka et al., 1993; Voigt &
Klausen, 1990) even when the movement patterns of the resistance and task
training exercises are similar (Tanaka et al., 1993). Third, while much
research has focussed on changes in the nervous system with training,
relatively few studies have investigated changes in muscle architecture after
RT (Henriksson-Larsén et al., 1992; Kawakami et al., 1993, 1995; Rutherford
& Jones, 1992). Moreover, none have examined changes in both the nervous
system and muscle architecture after a period of concurrent resistance and
task training.
Given that, for most athletes, RT forms only part of a total training program, it
is important that adaptations to RT are described when task training is
performed concurrently. The purpose of the present study was first to
determine if changes in VJ, sprint run and strength tests were related to the
movement pattern or velocity of multi-joint, dynamic RT exercises in well-
trained subjects, and second to examine changes in the nervous and
muscular systems when the RT was performed concurrently with VJ and
sprint training (i.e. task practice).
7.2 METHODS
7.2.1 Subjects
Thirty active individuals from the University population volunteered for the
study (Age range = 18 – 26 yrs). Given the magnitudes of changes in
performance shown in studies investigating movement-specific adaptations,
an effect size of at least 1.0 was expected. A priori power analysis revealed
that ten subjects were required in each group to be 80% confident (i.e. power
= 0.8) of finding differences significant at the 0.05 level (Table 8.3.13, Cohen,
1988). Of the 30 subjects, 23 (eight women & 15 men) completed the study
with the largest portion of withdrawals resulting from injury sustained outside
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the study. This would have affected the power of tests. Male and female
subjects have been used in many strength/sprint training studies (Esbjörnsson
Liljedahl et al., 1996; Herbert et al., 1998; Hortobàgyi et al., 2000; Mannion et
al., 1994; Smith & Rutherford, 1995). Given the difficulty in recruiting athletic
subjects for the present study, both men and women were included to
increase subject numbers. All subjects had participated in sport at the
recreational or representative level, had a minimum of three months of weight
training experience, could produce a force equal to twice their bodyweight
during an isometric squat lift, had no recent injuries or medical conditions that
would prevent maximal exertion. All subjects read and signed statements of
informed consent prior to participation in the study. The research was
approved by the Southern Cross University Human Ethics Committee
(Appendix B).
7.2.2 Protocol
Subjects participated in four weeks of resistance- and sprint/jump training
(familiarisation) prior to a second five-week (specific) training phase (Figure
7.1). During the four-week familiarisation phase, subjects performed two
sprint/jump sessions per week with each session involving one hour of
supervised training in sprint running and vertical jumping technique. The
purpose of such training was three-fold: 1) to ensure all subjects had
experience with sprint and jump technique so that ‘learning’ of the tasks was
minimal during the subsequent ‘specific’ training phase, 2) to improve the
reliability (decrease the variability) of the subjects’ performances, and 3) to
ensure subjects were training regularly prior to the first testing occasion.
In addition to the sprint/jump training, subjects also performed two supervised
weight training sessions per week. Each session involved performing three
sets of ten repetitions of reclined leg-press, deadlift, leg extension, leg curl
and standing calf raise exercises. If greater than 12 or less than eight
repetitions were performed in a set, the weight was adjusted for subsequent
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sets. The purpose of such training was to ensure all subjects were performing
weight training consistently prior to the study and that all subjects were
competent lifters. Attendance at training sessions was monitored and
subjects who did not perform a minimum of six sprint/jump and six RT
sessions over the four-week period were excluded from the study. Given that
all subjects had been performing RT, and training involving sprinting and
jumping, prior to the study those subjects recruited for the specific training
phase could be considered well-trained.
Following the four-week familiarisation phase, subjects were divided into three
training groups with male and female subjects distributed equally among the
groups. These groups were named squat (SQ), forward hack squat (FHS)
and sprint/jump (SJ) based on their training (see over). Briefly, all groups
performed at least two sprint/jump sessions per week with SQ and FHS also
performing two weight training sessions and SJ two additional sprint/jump
sessions (i.e. four sessions) each week. By the end of the study the SQ, FHS
and SJ groups contained eight, seven and eight subjects respectively (each
group contained at least two females, thus male/female ratios were similar
between the groups).
After the four-week familiarisation phase, but before the five-week specific
training phase, subjects performed 20 m sprint, vertical jump, squat lift,
forward hack squat and isokinetic leg extension tests (pre-test). On a
separate day, EMG was collected from leg musculature during performance of
vertical jump and sprint tasks. Collecting EMG on a separate day would have
minimised the effects of fatigue on the EMG recordings. Muscle thickness,
Familiarisation
(4 weeks)
Pre-test Specific training (5 weeks)
Four groups: SQ, FHS & SJ
Post-test
Figure 7.1. Overview of training and testing. A familiarisation phase preceded the 5-week ‘specific’ training phase to ensure all subjects were currently training. Testingwas performed before and after the specific training phase.
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pennation and fascicle length were also measured at two regions of both
the vastus lateralis and rectus femoris muscles (see over). The tests were
repeated after the five-week specific training phase (post-test). Three days of
rest separated the last training session of each phase from the testing.
7.2.3 Testing
7.2.3.1 20 m sprint
Times to sprint 10 m and 20 m were recorded using the same protocol
described previously (see Study Four). Briefly, subjects performed three
maximal sprints from a standing start. Electronic timing gates at 0, 10 and 20
m recorded time. The best running time to the 10 m and 20 m marks were
taken as that subject’s performances.
7.2.3.2 Vertical Jump
Subjects performed single- and double-leg vertical jumps using the same
protocol as described previously (see Study Four). Briefly, subjects
performed countermovement jumps with arms crossed over the chest. Jump
height was measured by a cable position transducer; the cable was
connected to a belt secured around the subject’s waist. The greatest jump
height recorded in three trials for both one- (subject’s preferred leg) and two-
legged jumps was taken as a measure of jump performance.
7.2.3.3 Squat lift
Subjects performed dynamic, free-weight squat lifts (minimum internal knee
angle was 90o) and isometric squats as described previously (see Study
Four). The descending phase of the squat lift was performed at a moderate
speed (1-2 s) but the ascending phase was performed maximally. In most
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instances the subject’s feet left the force platform at the end of the
movement and is best termed a ‘jump squat’ (JSQ). The maximum force
produced during the squat lift was taken as a measure of performance.
Testing maximum isometric strength rather than 1-RM strength would have
improved subject safety while allowing good measurement of subjects’ task-
specific strength. Testing of the relationship between dynamic and isometric
squat maximums suggested that weights of 30% and 60% of isometric
maximum correspond to weights of 44% and 88% of dynamic maximum (see
Study Two). Thus force produced during these efforts may indicate the
subjects’ ability to lift lighter and heavier loads rapidly.
7.2.3.4 Forward hack squat
Subjects performed both isometric and dynamic single- and double-leg FHS
as described previously (see Study Four). For the dynamic FHS, subjects
lowered the sled (including weights) at a moderate speed (1-2 s downward
phase) but performed the concentric phase at maximum velocity. A metal
stop was placed such that a spring attached to the sled contacted the stop at
the top of the movement, but before the subjects’ feet left the foot platform.
Therefore, subjects could provide maximum force throughout the concentric
phase without concern for injury. The maximum force produced during FHS
lifts (disregarding the force produced during impact of the sled with the metal
stop) was taken as a measure of performance. The minimum internal hip
angle was 90o and the internal knee angle was 110o. This approximated the
hip and knee angles during push-off in the acceleration phase of sprint
running (Jacobs & Ingen Schenau, 1992). Testing of the relationship between
dynamic and isometric forward hack squat maximums suggested that weights
of 40% and 70% of isometric maximum correspond to weights of 35% and
62% of dynamic maximum (see Study Two).
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7.2.3.5 Isokinetic knee extensor torque
Concentric, isokinetic knee extensor torque of each subject’s right leg was
tested at joint angular velocities of 30o.s-1 and 180o.s-1 using a KinCom
Isokinetic Dynamometer (Chatanooga Inc., USA). Subjects sat with a hip
angle of 90o and were secured by straps across the chest and waist. Gravity
correction of the subject’s limb was performed and anatomical references
defined. To define the anatomical reference, joint angle was measured during
a maximal knee extension contraction and this angle entered into the
computer. Often, angles are defined under passive conditions and the joint
angle during contraction can be different to that measured by the
dynamometer. In our case, the joint angle measured by the dynamometer
was very close to the joint angle actually achieved during the maximal
contractions. During testing, subjects performed two sets of four repetitions of
isokinetic knee extension and flexion at an angular velocity of 180o.s-1, then
three maximal repetitions of knee extension and flexion at 30o.s-1.
Only force data collected during knee extension was used for analysis. From
this, the maximum torque produced at both speeds was calculated, as was
the angle at which the maximum torque was produced at 30o.s-1. The angle of
maximum torque at 180o.s-1 was not used for analysis since torque at this
speed was highly variable both within and between subjects. The knee joint
angle during the concentric movement phase ranged from an external angle
of 95o (knee flexed) to 10o (knee extended) however only data collected from
knee extension between the angles of 80o and 20o was used for analysis. As
such, torque peaks associated with the impact of the tibia against the force
transducer early in the concentric phase were not included in the analysis.
7.2.3.6 Muscle Size and Architecture
While in a supine position subject’s knees were flexed to 90o and supported
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by the researcher. After applying hypoallergenic, water-soluble
transmission gel to the skin, a qualified sonographer used an 8 MHz linear
ultrasound transducer (Acuson 8L5, California, USA) to scan the surface of
the thigh to locate the muscle-tendon junction at the distal end of the rectus
femoris muscle (RF d). The point was clearly identified since the muscle
appears dark, but the tendon light, on the computer screen (see Figure 7.2).
The areas of transition from muscle to tendon appeared small (approximately
one centimetre). The transducer was then moved two centimetres proximally
where muscle thickness (distance between the superficial and deep borders
of the muscle) was calculated from a transverse section by an Acuson
Sequoia 512 system (Acuson, California, USA) after the muscle was manually
traced on the image screen. The distance to this point was measured on a
line from the joint cleft at the lateral condyle of the femur to the palpable
centre of the greater trochanter (Figure 7.3). The scanning head was then
rotated to view a longitudinal section of the muscle where the aponeurosis of
the muscle and fascicles attached to it were clearly visible. A photograph
(computer-aided transparency) of the ultrasound image was taken for
subsequent pennation measurement. The scanning head was then moved
proximally and muscle thickness measured at regular intervals along the
Figure 7.2. The muscle-tendon junction of rectus femoris was determined by moving thescanning head (ultrasound) distally along the thigh. Diagram A shows the dark centre of rectusfemoris and the white connective tissue that surrounds it (circled). The muscle-tendon junctionwas defined as the point at which the whole of the muscle became white. A longitudinal section(Diagram B) where the rectus femoris can been seen to taper from dark muscle to whiteconnective tissue can verify this.
A B
Rectus femoristapers
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muscle. At a point where the muscle thickness was deemed greatest, the
measures were repeated. This point was named RF p (proximal rectus
femoris). Measures of muscle thickness and pennation after the five weeks of
training were taken as close as possible to these sights after measuring the
distances from the lateral condyle. Repeatability of the measures was
practiced prior to testing to ensure reliability and has been demonstrated
previously (Giorgi et al., 1999). The reliability of the sonographer has been
determined previously (Ostrowski et al., 1997).
For the vastus lateralis muscle, measures were taken with the subject
remaining in a supine position with the knee flexed to 90o. Measures of
muscle thickness and photographs for pennation assessment were taken two
centimetres from the most distal muscle point (VL d – distal vastus lateralis)
and at the point of greatest muscle thickness (VL p – proximal vastus
lateralis). Again, the distances to these points were measured from the lateral
condyle.
Figure 7.3. Muscle thickness, pennationand fascicle length estimates weremade at two sites of the rectus femorisand vastus lateralis muscle usingultrasound. These sites are shown inthe diagram and described in the text.
RF – Rectus femorisVL – Vastus lateralis
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Pennation measurement
The angles of three fascicles were measured manually three times on the
photograph transparency of the ultrasound image by a goniometer and the
angle for each fascicle taken as the median of the three recordings. The
fascicle angle was measured at the fascicle-aponeurosis junction. As such
slight fascicle curvature was not accounted for (Kawakami et al., 1993). The
mean of the median angle of the three fibre bundles was considered the
muscle pennation angle. The bundles chosen were contained within two
centimetres of each other in the muscle. Reliability of pennation
measurement has been shown (Kawakami et al., 1993; Henriksson-Larsen et
al., 1992) and reliability of our pennation measurements has also been shown
(Blazevich & Giorgi, 2001).
Estimation of fascicle length
Fascicle length (FL) at each region on the two muscles was estimated as the
length of the hypotenuse of a triangle with an angle equal to the pennation
angle (θ) and the side opposite to this angle equal to the muscle thickness (T).
Therefore, FL=T/sinθ. Fascicle length is commonly estimated by this method
(Henriksson-Larsén et al., 1992; Kawakami et al., 1995; Kumagai et al.,
2000). Nonetheless, more recently digital measures have been used where
the fascicle length is measured after tracing it from ultrasound photographs.
We have compared the two methods, the results are presented in Appendix
F). Briefly, mathematical estimation is less reliable than the digital method
making significant changes in fascicle length harder to detect. Given the
results in Appendix F, we predict an error of up to five millimetres may be
expected in the present study using the mathematical method. Digital
techniques were not available for use in this study.
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5.2.3.7 Electromyographic (EMG) analysis
EMG recordings of five muscles of the right leg (gluteus maximus, biceps
femoris [long head], psoas major, rectus femoris and vastus lateralis) were
analysed for contraction/co-contraction patterns after subjects performed both
two-legged vertical jumps and sprint runs. After hair removal and light
abrasion with sandpaper to decrease skin resistance, stainless steel, bipolar,
pre-amplified surface electrodes (inter-electrode distance = 20 mm) were
placed over the muscle belly’s of the five muscles (see Table 7.1). The
recording electrodes were oriented parallel to the predicted line of muscle
fibres. The leads from the electrodes were attached to 6 m extension leads to
allow the subjects to move over a 12 m distance. Subjects then performed
two maximal vertical jumps and two maximal sprints over 8 m such that the
right leg contacted the ground on at least three occasions. A video camera
operating at 50 Hz (shutter speed 1/1000 s) captured the movement on tape
and EMG data collection commenced immediately as the subjects were
instructed to perform the jump or sprint. A light-emitting diode placed in the
camera’s view was illuminated at the same time so the EMG could be
synchronised to the movement. During the movements, raw EMG signals
sampled at 1000 Hz were amplified and collected using A/D conversion
(DT01EZ; Data Translation, USA) by personal computer (386 DX IBM-
compatible). High frequency noise was reduced by a 500 Hz anti-alias filter
and low frequency noise (particularly that caused by movements of the long
electrode cables) was minimised by passing the raw signals through a 10 Hz
high-pass filter. The data was then stored for subsequent analysis.
The VJ was analysed as two parts, the first being the descending or eccentric
phase and the second being the ascending or concentric phase. The sprint
run was likewise divided into two parts, the first being from first contact of the
foot with the ground (foot-ground contact; right foot) to the first contact of the
contralateral (left) foot with the ground, and the second being from
contralateral foot-ground contact to foot-ground contact of the first (right) foot.
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For all subjects, the stride analysis started from the first contact of the right
foot after the subjects had left the starting position. To determine the sections
of EMG used for analysis, the video was analysed for event times. The
associated EMG was then rectified and then averaged in bins of 5% of
movement time. The two phases of each movement were analysed
separately so that the first 50% of the EMG output related to the first
movement phase while the second 50% related to the second movement
phase. Thus, the different phases of the movements were time-normalised.
The EMG data were analysed by two methods. First, EMG recorded during
each 5% period were normalised to the greatest EMG recorded in any 5% bin
for a particular muscle in that movement. Thus an indication of the magnitude
of EMG detected during the movements was obtained. Second, muscle co-
contraction patterns were calculated for the sprint run and muscle activity
onset times calculated for the VJ. A ten-point moving average (1% of
movement time) was applied to the rectified data before determining muscle
burst onset (on) and offset (off) times. Each muscle was analysed separately
and deemed ‘on’ when ten consecutive samples of EMG exceeded a
threshold of 15% of the maximum amplitude of EMG collected for the duration
Table 7.1. Details of electrode placements on the five thigh muscles.
Muscle Electrode placement
Gluteus maximus (GL) Centre of the palpable part of the muscle with the electrodealigned diagonally downwards in line with the fibres
Biceps femoris (BF) A point 50% of the distance from the gluteal fold to the poplitealcrease on a line drawn vertically up the thigh from the palpabletendon on the lateral aspect of the lower, posterior thigh.Subjects flexed the knee to cause contraction of the muscle toensure electrode placement on the belly of the muscle. Theelectrode was aligned parallel to the femur.
Vastus lateralis (VL) A point 50% of the distance from the lateral border of the patellato the greater trochanter and on the line joining these landmarks.The electrode was aligned such that the long axis of the electrodeconfiguration passed through the patella’s centre.
Rectus femoris (RF) A point 50% of the distance from the most medial palpable pointof the inferior superior iliac spine to the middle of the superiorborder of the patella and aligned parallel to the femur (thus thecomplex pennation of RF was not accounted for).
Psoas major (HF; hipflexor
Immediately below the inguinal fold and 2 cm medial to theanterior superior iliac spine. Aligned parallel to the femur.
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of the task. A 15% threshold was selected after trialing thresholds ranging
from 5% to 30% and comparing the on and off times derived manually. The
muscle was deemed ‘off’ when the EMG amplitude diminished to less than
15% of the maximum normalised EMG for ten consecutive samples. On and
off times were checked manually after analysis to reduce the risk of identifying
the muscle as ‘on’ when the muscle was relatively inactive (type I error). This
method of determineing on/off times has been previously presented (Steele &
Brown, 1999).
Muscle co-contraction changes (sprint run) for two pairs of muscles (GL/HF
and VL/BF) were evaluated. The analysis was run for three separate data
sets. First, the percent of movement time in which both muscles were active
in the first and second phases of the movements (i.e. foot-ground contact and
recovery phases for running, and descending and ascending phases of the
vertical jump) was calculated. Two further data sets were calculated, one
where co-contraction patterns were normalised to the average time in which
the muscles were labeled ‘on’ (average of percent time in which one muscle
was ‘on’ and the percent time the second muscle was ‘on’), and a second
where co-contraction patterns were normalised to the ‘on’ time of the muscle
that was active longest during the movement.
Specific terms have been used to describe certain phases of the sprint
running movement. These include:
Acceleration phase of the sprint run – Considered as that part of a sprint run
beginning at the movement’s onset and ending when maximal (or near-
maximal) speed is reached. In the present study, the term refers more to the
early part of this phase when the body has a distinct forward lean. Jacobs &
Ingen Schenau (1992) described this phase by examining sprint runners from
the second to the fourth step of a sprint run from a stationary start.
Foot-ground contact phase – occurs when the foot first strikes the ground and
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ends when the foot leaves the ground.
Recovery phase – describes that part of the running stride from when the foot
leaves the ground to when the foot once again makes contact with the
ground.
Toe-off – refers to the precise moment when the foot leaves the ground (ie
between foot-ground contact and recovery phases).
7.2.4 Training
7.2.4.1 Training groups
Squat (SQ) training
Subjects in the squat (SQ) group used the free-weight squat lift as their
dominant training exercise during the specific training phase (supplemenatry
exercises are described later). The squat lift required subjects to lower their
body to a sitting or squatting position with a knee angle of 90o with a weighted
bar rested across the shoulders then lift the weight back up to the starting
position. Subjects were guided to the correct knee angle by a supervisor
during each squat. Training was performed two times per week. In the first
session of each week (heavy day), subjects performed three warm up sets of
the squat lift (see Appendix D for details) followed by three sets of six squats
with weights equal to 50% - 80% of their pre-determined isometric maximum
force (described earlier). Three minutes rest separated sets. Weights were
increased when subjects could perform more than six repetitions in a set. The
weight lifted throughout the five weeks of training increased from 50 – 60% to
70% - 80%. In some instances, subjects lifted up to 90% of their
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predetermined isometric maximum in sessions toward the end of the
training period. In the second session of each week (light day), subjects lifted
weights equal to 30 – 50% of their isometric maximum for three sets of six
repetitions. No subjects were allowed to lift more than 50% of their
predetermined isometric maximum regardless of strength gains. In both
sessions, the ascending (concentric) phase of the squat was performed at
maximum velocity such that the subjects’ feet left the ground. Thus, the squat
could be considered a jump-squat. The loads were different between
sessions to provide a different movement stimulus (Wilson et al., 1993) and
prevent subjects becoming accustomed to the training. Typical training
sessions for heavy and light days are presented in Appendix D.
In addition to the squat lift training, SQ subjects also performed two sets of ten
repetitions of a back extension exercise, three sets of eight repetitions of a leg
curl (knee flexion) and two sets of eight standing calf raises. All sets were
performed with a weight that allowed movement failure within the allotted
number of repetitions on the heavy day, but could be performed with greater
movement speed and without failure on the light day. Subjects were also
encouraged to perform two sets of abdominal crunches and spend 15 minutes
stretching the major lower limb muscles after training. In addition to the
weight training, SQ subjects also performed two sprint/jump sessions per
week (see over).
Forward hack squat (FHS) training
Training performed by the forward hack squat (FHS) group differed to SQ only
in the exercise used as the dominant lift in weight training. FHS used the one-
legged FHS exercise as their dominant training exercise during the specific
training phase (Figure 7.4). Thus, in contrast to SQ, training was performed
unilaterally since sprint running is performed unilaterally and some research
(Häkkinen et al., 1996; Rube & Secher, 1990; Tanaguchi, 1997) has shown
that adaptations to RT can be specific to the laterality of training exercises.
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Within each session, legs were trained alternately with one set being
performed with the right leg and the next with the left. Training was performed
twice a week (same as SQ). In both sessions, the concentric (upward) phase
of the FHS was performed at maximum velocity such that the sled on which
the weights were placed was moved forcefully into a spring at the top of the
movement. The spring height was set individually for each subject. Typical
training sessions for heavy and light days are presented in Appendix D.
Sprint/jump (SJ) training
Subjects in the sprint/jump (SJ) group did not perform weight training during
the five-week specific training phase. Instead, SJ subjects participated in four
sprint/jump sessions. Thus, the total number of training sessions performed
by all training groups was the same.
7.2.4.2 Sprint and jump training
SQ and FHS subjects performed two sprint/jump training sessions per week
while the sprint/jump (SJ) group performed four sessions per week. The
Figure 7.4. Single-leg forward hack squat. These diagrams show clearly the body position andlaterality of the task. The ‘free’ leg can also be seen flexing while the ‘working’ leg extends.This movement was performed in an attempt to better simulate the acceleration phase of sprintrunning.
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sessions typically lasted one hour and consisted of a ten minute warm-up,
five minutes stretching, 35 min of sprint and jump training and another ten
minutes of stretching at the end of the session. The sprint/jump sessions
were divided into a sprint component and jump component. During the sprint
component, subjects predominantly practiced running over distances up to 30
m using the techniques previously taught to them. A qualified sprint coach
who was unaware as to the group allocation of subjects supervised all
sessions for each group. Subjects often ran up to 20 sprints in a session with
training volume increasing over the nine weeks of training (four-week
familiarisation and five-week specific training phases). The jump component
typically consisted of both one- and two-legged jumps in sets of three to five
repetitions. Subjects practiced jumping with different countermovement
distances in order to find their optimum knee bend. Subjects were also
expected to perform the jumps maximally and ensure complete extension of
the hip, knee and ankle joints at take-off.
Sessions typically consisted of 20 jumps separated by rest. The training load
was increased over the nine weeks of training. The intensity of the runs and
jumps was always maximal, however the volume of work increased. In the
first week of training, two sets of three sprint runs were separated by two
minutes of rest. Two sets of three vertical jumps were also performed with
one minute of rest separating sets. By the end of the study, four sets of four
sprints with two minutes rest were performed with four sets of four vertical
jumps. For SJ subjects, sprint sessions could not be performed on four
consecutive days. Sprint training may, for example, be performed on
Monday, Tuesday, Thursday and Saturday. For SQ and FHS subjects sprint
sessions were performed on different days to the RT and one rest day
separated the four sessions. For example, sprint sessions may have been
performed on Monday and Thursday with RT sessions being performed on
Tuesday and Friday.
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7.2.5 Data analysis
After satisfying the assumptions of homogeneity of variance (Lavene’s test),
sphericity (Mauchly’s test) and normal distribution of data (Kolmogorov-
Smirnov test), performance changes with training (sprint run, VJ, SQ and
FHS) were analysed using Repeated Measures ANOVA (SPSS v10.0, SPSS
Inc) with ‘group’ as the between subjects factor and ‘time’ (pre- to post-
training) as the within subjects factor. When significant group effects were
revealed, Tukey’s HSD post-hoc analysis was used to determine differences
between the three groups. For all analyses, significance was set at an alpha
level of p<0.05, unless otherwise stated.
Analyses of muscle thickness, pennation and fascicle length were performed
separately. For each measurement site, Repeated Measures ANOVA
examined significant effects of group and time. Interaction effects were
further analysed by one-way ANOVA of difference scores (ie. pre- to post-
training changes). Bonferroni post-hoc analysis tested for significant
differences. In the event of non-homogeneous distribution of data,
Tamhane’s T2 post-hoc analysis was used. Tamhane’s T2 post-hoc analysis
does not assume equal variances. To examine the relationships between
muscle thickness, pennation and fascicle length at each site on the muscles,
Pearson’s Product Moment correlation coefficients were computed on the
difference scores (absolute variable changes from pre- to post-training). In
order to control for type 1 error, significance was set at p<0.01.
Changes in isokinetic knee extension torque produced during contractions at
two speeds were compared using Repeated Measures ANOVA with ‘training
group’ as a between-group factor. Differences in the torque produced at the
different speeds, and changes in the angle at which peak torque was
produced were analysed. Between group effects were further analysed by
Tukey’s HSD post-hoc test.
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Electromyogram data were analysed in two ways. First, changes (±95%
confidence intervals) in normalised EMG for each muscle were calculated for
each 5% of movement. Paired t-tests with Bonferroni correction were used to
assess differences between groups. Due to loss of data, only ten subjects
were included in the analysis. Four subjects had performed RT (SQ and FHS
subjects) while six performed only sprint and jump training (SJ subjects). As
such, comparisons were made only between weight-trainers and SJ subjects.
No comparison was made between SQ and FHS groups because the low
subject number and large number of t-tests performed would have made
significant results unlikely (Perneger, 1998). Therefore effect sizes were
calculated to provide a description of between-group differences without
concern for sample size. In order to control for type I error rate only effect
sizes greater than 1.0 (i.e. between-group differences were greater than the
pooled standard deviation) were deemed large and of statistical importance.
Changes in muscle co-contraction (sprint run) and muscle activity onset times
(VJ) for gluteus maximus and psoas major (GL/HF), and vastus lateralis and
biceps femoris (VL/BF) muscle pairs were compared between the groups
(again, comparisons were only made for ten subjects. As such, comparisons
were made between weight-trainers and SJ subjects) by Repeated Measures
ANOVA. ‘Group’ and ‘movement phase’ were submitted as between-group
factors.
For all Repeated Measures ANOVA’s, power analysis was also performed to
examine the likelihood that significant effects could be detected. When power
was low (power < 0.8) effect sizes were calculated on near-significant results
(p<0.1) to examine differences without concern for sample size. When
significant group effects were revealed, Tukey’s HSD post-hoc analysis was
used to determine differences between the three groups. For all analyses,
significance was set at an alpha level of p<0.05, unless otherwise stated.
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7.3 RESULTS
7.3.1 Performance Changes with Training
There were no differences between the groups’ performances either before or
after the training in any strength, VJ or sprint test. There was however an
effect of time (p< 0.01) such that, for many strength and performance
measures, subjects improved over the five weeks of training. Pre- and post-
training test performances of all subjects (pooled) are presented in Table 7.2.
Test Variable Pre-test 95% CI Post-test 95% CI Mean
Change
p-value
10 m sprint (s) 1.91 1.78-2.02 1.86 1.77-1.95 -0.05 <0.05
20 m sprint (s) 3.26 3.00-3.47 3.22 3.05-3.40 -0.04 NS
VJ 1L (m) 0.29 0.25-0.33 0.28 0.25-0.32 -0.01 NS
VJ 2L (m) 0.40 0.34-0.46 0.41 0.36-0.46 +0.01 NS
FHS 1L iso (N) 1186 1030-1342 1455 1256-1654 +269 <0.01
FHS 2L iso (N) 1817 1558-2077 2108 1827-2389 +291 <0.01
FHS 2L 40% F (N) 1249 1055-1444 1277 1091-1463 +28 NS
FHS 2L 70% F (N) 2012 1721-2304 1952 1703-2201 -60 NS
FHS 2L 40% Velp (m.s-1) 1.60 1.51-1.68 1.19 1.14-1.24 -0.41 <0.001
FHS 2L 70% Velp (m.s-1) 1.13 1.04-1.23 1.19 1.14-1.24 +0.06 NS
SQ iso F (N) 1731 1573-1889 1743 1589-1896 +12 NS
SQ 30% F (N) 1937 1729-2145 2048 1866-2230 +111 <0.05
SQ 60% F (N) 2327 2022-2632 2374 2126-2622 +47 NS
Table 7.2. Pre-training, post-training and change scores for sprint, VJ, FHS and Squat tests (allsubjects pooled). There was an increase in some strength measures and decrease in 10 msprint time (p<0.05). There were no between-group differences.
NS – Not statistically significantVJ – vertical jump, FHS – forward hack squat, SQ – squat.iso – isometric contraction30%, 40%, 60%, 70% - load as a percent of isometric maximumVelp – Peak movement velocity1L – single-leg2L – double-leg
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7.3.2 Isokinetic Knee Extension Torque
7.3.2.1 Angle of peak torque
Reliability of measures of the angle at which peak torque was produced (APT
– Angle of Peak Torque) were poor at 180o.s-1, but were good at 30o.s-1 (see
Table 7.3). Thus changes in APT were analysed only for the slow speed.
There was a near-significant (p<0.07) increase in APT (i.e. the knee angle
was closer to 90o) when all subject data was combined for all groups,
however there was no difference between the groups (see Table 7.4).
Statistical power was low for both main effect (Power = 0.44) and interaction
(Power = 0.39) analyses making it unlikely that significant effects would be
seen. Effect sizes (ES) were thus calculated to examine performance
changes without concern for subject sample size. The effect statistics
suggest that changes in APT may have differed between SQ and FHS (ES =
0.71) and SQ and SJ (ES = 0.90) groups with the knee angle for SQ subjects
being greater (more flexed) after training. Low subject numbers in the present
study may therefore have prevented significance being reached.
Angular Velocity Statistic Score Lower 95% CI Upper 95% CI
30o.s-1 Change in mean 0.61o -2.54 1.32
ICC 0.85 0.64 0.94
180o.s-1 Change in mean 1.18o -1.56 3.91
ICC 0.63 0.26 0.84
Table 7.3. Reliability statistics for angle of peak torque. Inter-repetition reliability for the slow(30o.s-1) movement was better than for the fast movement (180o.s-1).
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Pre-testing Post-testing
Mean (o) SD Mean (o) SD
FHS 65.7 9.3 67.3 5.9
Squat 62.0 6.9 68.3 3.5
Sprint/jump 61.1 11.9 61.4 6.4
7.3.2.2 Velocity-specific isokinetic torque changes
Subjects produced more knee extension torque at 30o.s-1 than 180o.s-1 (246.7
± 62.6 Nm and 161.8 ± 45.1 Nm respectively; p<0.001) although there were
no significant between-group differences after training. Thus there were no
training-related changes in isokinetic knee extension torque at either
contraction velocity.
7.3.3 Muscle Size and Architecture
7.3.3.1 Muscle thickness
Mean muscle thickness for each training group at each test occasion is
presented in Table 7.5. There was an overall increase in muscle thickness
after training (p<0.05). However, the increase was not different between the
groups (see Figure 7.5). Thus, muscle thickness generally increased in both
muscles in response to training but the change was not related to the training
performed by the subjects. Given the low statistical power of the tests (power
< 0.6), effect sizes were calculated on near-significant results (p<0.1). At
VLd, muscle thickness of FHS subjects decreased relative to both SQ and SJ
(ES = 0.96 and 1.9 respectively). There was no apparent difference between
SQ and SJ. At VLp, muscle thickness of SQ and FHS increased more than
SJ (ES = 1.18 and 0.78 respectively). At RFd, muscle thickness of FHS and
SJ increased more than SQ (ES = 1.27 and 0.90 respectively). While there
Table 7.4. Angle of peak torque (0o = full extension) pre- and post-testing. There wereno differences between the groups.
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was a small difference between FHS and SJ (with muscle thickness of FHS
increasing more, ES = 0.43), the difference was small. There were no
apparent differences between the groups at RFp.
Table 7.5. Mean (±SD) pre- and post-test muscle thickness and change in thickness. Meanchange values are rounded to two significant figures and are not calculated from thepreviously-rounded pre- and post-test scores. There were no between-group differences inchanges in muscle thickness, however there was an overall increase in muscle thicknessacross all groups at each muscle site (p<0.05*) except VL d. VL d – vastus lateralis distal, VL p– vastus lateralis proximal, RF d – rectus femoris distal, RF p – rectus femoris proximal.
Muscle Pre-test
Mean (mm)SD
Post-test
Mean (mm)SD
Change*
Mean (mm)95%Confidence interval
SQ VL d 13.0 3.9 13.6 3.8 0.6 -0.4 – 1.6VL p 23.4 4.4 26.0 3.6 2.6 0.8 – 4.3RF d 13.4 2.3 13.6 3.2 0.2 -1.3 – 1.7RF p 24.0 2.6 25.9 2.2 2.4 0.7 – 4.2
FHS VL d 13.9 2.8 11.3 2.8 -2.6 -9.2 – 4.0VL p 20.0 0.8 22.3 1.4 2.3 0.1 – 4.5RF d 11.1 1.6 14.2 2.0 3.1 -0.6 – 6.8RF p 23.0 1.6 25.5 2.6 2.5 0.7 – 4.3
SJ VL d 11.0 0.6 12.4 2.0 1.3 -1.3 – 4.0VL p 21.0 2.1 21.6 1.7 0.7 -0.8 – 2.2RF d 11.4 1.0 13.8 2.8 2.3 -0.7 – 5.4RF p 20.8 3.3 25.0 4.1 4.2 0.9 – 7.5
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Figure 7.5. Muscle thickness changes for all muscle sites. There was a significant increasein muscle thickness after training (p<0.05) but no difference between groups. Solid barsrepresent mean scores while error bars represent the 95% confidence intervals of thechange in muscle thickness.
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7.3.3.2 Muscle pennation
Mean pennation for each training group at each test occasion is presented in
Table 7.6. Statistically significant (p<0.05) changes in pennation were only
seen at VLd where pennation increased after SQ and FHS training but
decreased after SJ training (Figure 7.6). Given the low statistical power of the
tests (power < 0.6), effect sizes were calculated on near-significant results
(p<0.2). For both VL p and RF d, squat and FHS groups showed increases in
pennation while SJ decreased. At VL p effect sizes for the differences in
pennation change scores were 1.08 and 0.78 for SQ and FHS respectively
when compared to SJ. At RF d effect sizes were 0.98 and 1.45. Thus there
was a trend toward greater increases in pennation of muscles of SQ and FHS
subjects that should be followed up in future research.
Table 7.6. Mean (±SD) pre- and post-test muscle pennation and change in pennation. There wasa significant difference in the change in pennation between both the SQ and SJ, and FHS and SJfor VL d (p<0.05*). VL d – vastus lateralis distal, VL p – vastus lateralis proximal, RF d – rectusfemoris distal, RF p – rectus femoris proximal.
Muscle Pre-test
Mean (deg) SD
Post-test
Mean (deg) SD
Change
Mean (deg) Confidence interval
SQ VL d 8.3 1.8 8.8 0.8 0.5 -1.4 – 2.4VL p 9.9 2.2 11.4 1.6 1.5 -0.5 – 3.5RF d 4.1 1.1 5.4 1.0 1.3 -0.2 – 2.8RF p 10.9 3.1 10.1 1.7 -0.9 -4.5 – 2.6
FHS VL d 8.8 0.5 9.9 1.8 1.1 -1.4 – 3.7VL p 10.0 3.2 11.3 3.1 1.3 -1.7 – 4.2RF d 4.1 0.6 6.0 1.2 1.9 0.2 – 3.5RF p 8.3 3.6 9.0 2.1 0.8 -7.5 – 9.0
SJ VL d 9.9 0.7 6.8 0.8 -3.1* -4.0 - -2.2VL p 9.6 1.8 9.0 1.6 -0.6 -2.7 – 1.5RF d 5.4 1.4 5.2 2.6 -0.2 -4.4 – 4.0RF p 10.7 5.2 11.3 5.6 0.6 -0.8 – 2.0
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Figure 7.6. Change in muscle pennation for all muscle sites. At VL d, SQ and FHSincreased pennation while SJ decreased (p<0.05*). There were no other significantchanges. Solid bars represent mean changes in pennation while error bars represent 95%confidence intervals for the change in pennation.
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7.3.3.3 Fascicle length
Mean estimated fascicle length for each training group at each test occasion
is presented in Table 7.7. At VLd, fascicle lengths for SJ subjects increased
while there were no changes in SQ and FHS subjects. This was reflected in a
significant group × time interaction effect where fascicle lengths of SJ subjects
changed differently to both SQ and FHS subjects (p<0.05; Figure 7.7). At VL
p, there was a non-significant trend toward a group × time interaction (p=0.08;
ES = 4.33) such that again, SJ increased while FHS and SQ did not change.
Thus for vastus lateralis, fascicle length did not change for the SQ and FHS
groups, but increased significantly for SJ.
There were no differences between the groups’ fascicle length changes in the
rectus femoris although for the proximal part of this muscle, fascicle length
increased overall after training (p<0.05). Therefore, training group did not
influence fascicle length of the rectus femoris.
Table 7.7. Mean (±SD) pre- and post-test estimated fascicle length and change in fasciclelength. At VL d there was a significant difference in the change in fascicle length between SQand SJ, and FHS and SJ (p<0.05a). There was also a near significant difference between SQ andSJ for VL p (p=0.08b). Estimated fascicle length increased for RF p with no differences betweenthe groups. VL d – vastus lateralis distal, VL p – vastus lateralis proximal, RF d – rectus femorisdistal, RF p – rectus femoris proximal.
Muscle Pre-test
Mean (deg) SD
Post-test
Mean (deg) SD
Change
Mean (deg)95%Confidence interval
SQ VL d 92.2 28.0 88.5 17.1 -3. 7a -24.3 – 16.9VL p 140.0 29.1 133.0 16.2 -6.1b -37.9 – 24.7RF d 170.0 42.1 207.4 69.4 51.6 -53.0 – 128.2RF p 117.9 34.0 216.1 16.5 -6.6 44.3 – 152.2
FHS VL d 78.9 18.6 71.9 22.9 10.5a -31.6 – 19.5VL p 108.1 53.0 113.9 38.6 32.2 -20.0 – 41.0RF d 131.7 11.9 137.7 33.3 37.6 -63.7 – 65.0RF p 160.1 97.0 181.9 64.0 0.6 -180.3 – 240.6
SJ VL d 64.4 7.1 116.0 15.8 67.5a 31.3 – 71.8VL p 129.3 27.0 161.5 24.1 98.3b 9.9 – 54.6RF d 127.3 41.5 194.9 48.8 31.6 -73.1 – 208.2RF p 106.2 29.3 147.8 36.8 41.6 10.9 – 72.3
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Figure 7.7. Change in fascicle length for all muscle sites. Fascicle length increased for SJat VL d (distal vastus lateralis) while there was no change for SQ and FHS (interactioneffect: p<0.05*). There was also a near-significant difference in the change in fascicle lengthbetween SQ and SJ at VL p (p=0.08+). There were no group differences in fascicle lengthfor rectus femoris. Solid bars represent mean changes in fascicle length while error barsrepresent the 95% confidence intervals for the change in fascicle length.
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7.3.3.4 Relationship between muscle thickness, pennation and
fascicle length
There was no correlation between changes in muscle thickness and
pennation or between changes in thickness and fascicle length. However,
highly significant correlations were found between muscle pennation and
fascicle length (r = -0.82 – -0.92, p<0.01; Table 7.8). Coefficients of
determination ranged from 0.67 to 0.85, therefore 67% - 85% of the variability
in fascicle length can be accounted for by changes in pennation, or vice
versa. Thus, while there was no relationship between muscle thickness and
pennation changes with training, there was a strong relationship between
pennation and fascicle length changes.
7.3.4 Electromyographic Changes
7.3.4.1 Changes in normalised EMG
Pre- to post-training changes in EMG amplitude (normalised to the greatest
EMG during the movement) were calculated for ten subjects. Of those, four
performed RT (SQ and FHS subjects) while six performed only sprint/jump
training (SJ). While low subject numbers likely yielded low statistical power,
Table 7.8. Results of correlation analysis on pennation and estimated fascicle lengthchanges after training. There was a strong relationship between pennation andfascicle length despite no relationship between thickness and either pennation orfascicle length.
Muscle site tested r r2 p-value
Distal vastus lateralis-0.84 0.71 <0.001
Proximal vastus lateralis -0.82 0.67 <0.001Distal rectus femoris -0.85 0.72 <0.001Proximal rectus femoris -0.92 0.85 <0.001
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data analysis was performed to determine trends that might have been
significant with a larger sample size. There were no differences between
those subjects who performed RT (SQ and SJ) and those who did not (SJ) in
the changes in normalised EMG during the sprint and VJ when univariate
tests were corrected for type I error rate (Bonferroni correction). Therefore,
effect sizes were calculated for 5% sections of movement to examine the
differences between groups without regard for sample size. A stringent effect
size of 1.0 was taken as a ‘large’ effect (Hopkins, 2000). In some cases
uncorrected p-values from t-tests performed on the data were used to indicate
parts of the movement where between-group differences were notable.
For running acceleration (see Figure 7.8) there was an increase in gluteus
maximus (GL) EMG in the weight-trained subjects from the point at which the
right foot left the ground to approximately the point at which the foot passed
under the body (45% - 70% of movement). No differences appeared for
biceps femoris (BF) although EMG for both groups decreased relative to pre-
training levels during foot-ground contact and then increased prior to foot-
ground contact. Thus BF may have been activated differently after training
regardless of the type of training performed by the subjects. Vastus lateralis
EMG of weight-trained subjects was greater from immediately after the right
foot left the ground to just prior to foot-ground contact (65% - 95% of
movement) suggesting greater muscle activity during the recovery phase of
the stride. For rectus femoris (RF), weight-trained subjects tended to increase
EMG prior to foot-ground contact (65 – 95% of movement) while there was no
change in SJ subjects. Finally, hip flexor (HF; psoas major) activity increased
in SJ subjects early in the foot-ground contact phase, and was elevated in
both groups around toe-off and early in the recovery phase. There was also a
marked decrease in HF activity immediately prior to foot-ground contact (90 –
100%) in weight-trained subjects. A t-test (not corrected for type I error rate)
found a significant difference between EMG changes in weight-trained and SJ
subjects in this part of the movement.
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% Movement Time
Figure 7.8. Change (±95% CI) innormalised EMG for five thighmuscles during the accelerationphase of a sprint run. There wereno differences between weight-trained subjects (dark line) andsprint/jump subjects (light line) forany muscle. Foot-ground contactoccurred at 0% of movement, thefoot left the ground at 50% ofmovement and then contacted theground again at 100% ofmovement.
GL – Gluteus maximusBF – Biceps femorisVL – Vastus lateralisRF – Rectus femorisHF – Hip flexor (psoas major)
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For VJ (see Figure 7.9) there was an increase in GL activity in weight-
trained subjects early in the descending phase (0 – 40% of movement) and
during the transition and early ascending phase (50 – 70% of movement).
However, late in the ascending phase, EMG of VL decreased in weight-
trained subjects (70 – 90%). Indeed t-tests revealed a significant (non-
corrected) difference between subjects who performed RT and those that did
not (significant differences from 75 – 80% and 85 – 90% of movement).
Similarly complex changes were seen in BF with the EMG of SJ subjects
decreasing late in the descending phase (35 – 40% of movement) and the
EMG of weight-trained subjects decreasing early in the ascending phase (60
– 70% of movement). Generally though, both groups produced less EMG
after training either late in the descending or early in the ascending phase, but
more during the middle of the ascending phase. There were no between-
group differences in the change in EMG for VL or HF, although for RF the
weight-trained subjects showed less muscle activity early in the descending
phase (5 – 25% of movement) with the difference being significant by t-test
(uncorrected; 5 – 10% of movement).
7.3.4.2 Changes in muscle co-contraction (sprint run) and activity onset
times (vertical jump)
There were no differences between changes in the co-contraction patterns of
weight-trained and SJ subjects in either phase of the sprint run and VJ
movements. While the observed power of the tests was generally poor
(<0.50) no comparisons approached significance. Thus effect sizes were not
calculated to examine the magnitude of differences without consideration for
sample size.
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-1.5
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Figure 7.9. Change (±95% CI) innormalised EMG for five thighmuscles during the performance of avertical jump. There were nodifferences between weight-trainedsubjects (dark line) and sprint/jumpsubjects (light line) for any muscle.Forward rotation of the upper body(which signalled the beginning of thedescending phase of the jump)occurred at 0% of movement, thetransition from the descending toascending phase occurred at 50% ofmovement, while the toe left theground at the end of the jump at100% of movement.
GL – Gluteus maximusBF – Biceps femorisVL – Vastus lateralisRF – Rectus femoris
HF – Hip flexor (psoas major)
% Movement Time
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7.5 DISCUSSION
This study aimed to describe short-term changes in both performance and
neuromuscular functioning after concurrent resistance- and sprint/jump
training. It was hypothesised that if rapid, movement pattern-specific changes
occurred the FHS-trained subjects should improve their sprint run more than
the SQ group, while the SQ-trained subjects should improve their VJ more
than the FHS group. The sprint/jump group was incorporated to determine
whether the addition of RT to a program affected performance differently to a
program where no RT is performed.
7.5.1 Performance Changes with Training
Neither RT per se nor the movement pattern of resistance exercises
influenced performance of SQ, FHS, sprint or jump tests. Several
explanations may be offered for the lack of training-specific performance
changes. First, the short (five-week) specific training phase may not have
been sufficient for meaningful changes to occur especially given that training-
induced performance changes are often marginal in athletes who have been
training for long periods (Häkkinen et al., 1987, 1991). However, there were
statistically significant performance improvements for the subjects as a whole
in many of the test variables. This suggests that the training period was long
enough for performance changes to occur. Furthermore, studies investigating
movement-specific changes to RT have shown significant effects after as little
as four weeks (Abernethy et al., 1996; Weir et al., 1994, 1995a,b) when RT is
performed in isolation (i.e. without accompanying task practice).
The lack of training-specific performance changes may also have resulted
from the three training groups each performing elements in training that were
beneficial to test performances, but no single group performing training that
was more advantageous than another group. As such, it is possible that all
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three training programs offered similar performance benefits over the short
training period used in the present study. Indeed Garnica (1986) observed
similar improvements in upper body, isokinetic muscle power in groups that
trained at slow (60o.s-1) and fast (180.o.s-1) speeds. Alternatively, variability in
subject’s training responses and the low subject numbers (23 in total) might
have made it difficult to show clear performance changes.
Improvements across all training groups may have resulted from subjects
training with extra vigor during the specific training phase. Häkkinen et al.
(1987) showed that improvements in strength and performance of highly
trained weightlifters in a one-year training cycle occurred during those periods
of training where training intensity was higher than normal. Similarly,
performances of subjects in the present study may have been improved if
their training intensity was higher than normal. An increase in training
intensity was likely given the training was somewhat novel. Also, subjects’
motivation might have been improved by the knowledge that their training
sessions were supervised and performance changes were to be assessed
after the training period. Given the likely increase in motivation a general
increase in training intensity and test performance could be expected.
Nonetheless, past research has also shown no performance differences
between groups who perform different types of RT with task training. Sleivert
et al. (1995) reported improvements in cycle ergometer power in subjects who
performed eight weeks of strength training and then six weeks of bicycle
sprint training that were similar to a group that performed sprint training for the
entire 14 weeks. This was despite between-group differences in some of the
physiological parameters measured. As such, examination of performance
changes should not be used as the sole indicator of the influence of combined
resistance- and speed training, especially when training is performed for short
periods. Delecluse et al. (1995) also reported no effect of RT movement
velocity on changes in running acceleration when subjects performed two
resistance and one sprint session a week for nine weeks. A high-velocity
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training group however improved their maximum running speed more than
a low-velocity group. Thus the results of the present study are similar to other
studies that have examined the effects of combined strength and speed
training on tasks involving high power outputs (eg cycle ergometer or running
acceleration).
7.5.2 Body Position-specific Strength Changes
Although the magnitude and timing of joint angle changes and laterality
differed between SQ and FHS exercises, one would expect that if body
position affected performance then some differences between SQ and FHS
groups would have been found given they had different body positions.
However there were no differences in the training responses between the
groups. Thus, it is possible, if not likely, that body position did not influence
test performances. Alternatively, a difference between the groups would not
have been conclusive evidence of an effect of body position given the other
factors that differed between the tasks.
7.5.3 Joint Angle-specific Strength Changes
Adaptations to RT are often specific to the joint angles through which force is
produced in training (Kitai & Sale, 1989; Lindh, 1979; Weir et al., 1994). In
the present study, the range of motion of the knee joint differed between SQ
and FHS groups with the knee angle of SQ subjects closing to 90o but the
knee angle of FHS subjects only closing to 70o (110o internal knee angle).
Given the 20o difference in knee range of motion between the groups, one
could anticipate post-training differences in the angle at which maximum
torque was produced (APT – angle of peak torque) during the knee extension
task.
Across all subjects, there was a near-significant increase in APT (i.e. shift
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toward increased torque at greater knee flexion; p<0.07) after training. The
increase was largely due to a shift in the APT of SQ subjects (Mean change =
6.3o ± 4.6) with little change in FHS and SJ subjects. Indeed effect size
statistics suggest that the change in APT for SQ subjects was far greater than
either FHS or SJ (ES = 0.71 and 0.90 for SQ versus FHS and SQ versus SJ
respectively). Changes in APT in that direction could be expected given SQ
subjects moved through a greater range of motion in training than both the
FHS (who trained to an internal knee angle of 110o) and SJ (who only
performed sprint and jump training, both of which require movements of less
than 90o at the knee during propulsive phases). The changes in APT
therefore could be considered evidence that, even during the concurrent
training of short duration performed in this study, angle-specific strength
changes occurred.
The mechanisms responsible for the small differences in APT between the
groups are not known. Certainly neural mechanisms have been implicated in
previous research (Kitai & Sale, 1989; Weir et al., 1994). However no EMG
measures were taken during the knee extension test. Muscular changes
might have also contributed however. Certainly a change in the length-
tension properties of fibres of the quadriceps muscle groups would have
resulted in changes in APT. Again, such changes were not monitored in this
study.
Muscular factors that influence the torque-angle relationship and were
measured in this study include the pennation and fibre length of quadriceps
muscles. The amount of force transmitted along a tendon from a contracting
fibre is inversely related to its angle of attachment, and since fibres of pennate
muscles rotate during muscular contraction, pennation and therefore the loss
of force is greater in muscles with greater pennation. Thus, there is a greater
reduction in relative force producing potential at short muscle lengths in highly
pennate muscles compared to muscles with smaller pennation. In this study,
pennation of the vastus lateralis and rectus femoris was not different between
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SQ and FHS subjects despite their APT changing differently. Therefore,
unless changes in vastus intermedius or vastus medialis had a significant
effect, it is unlikely that changes in pennation affected the APT of subjects in
this study.
Changes in fibre length can also change the length-tension properties of a
muscle (Goldspink, 1974; Williams et al., 1990). Decreases in fibre length are
associated with increases in passive tension and therefore a reduction in the
length at which optimum force is produced. Again, there were no differences
between SQ and FHS subjects. It is therefore unlikely that fibre length
changes affected APT of subjects.
7.5.3 Laterality-specific Strength Changes
Effects of laterality of training were investigated by comparing the
performances of SQ (who trained bilaterally) and FHS groups (who trained
unilaterally) on unilateral tests. There was no evidence for laterality-specific
adaptations as there were no between-group differences in unilateral VJ,
unilateral FHS or unilateral isokinetic knee extension performance after
training. The result might be due to the short training period or low subject
numbers. However, Tanaguchi (1997) reported significantly greater increases
in bilateral handgrip and leg extension strength after three weeks of training in
subjects who trained bilaterally as compared to subjects who trained
unilaterally. Thus, when resistance exercise was performed in isolation (i.e.
not concurrently with another mode of training) laterality-specific performance
changes seemed to occur rapidly.
It was also possible that the reliability of unilateral tests was low. This would
reduce the likelihood of detecting significant changes. Nonetheless, an
investigation of the reliability of the unilateral and bilateral FHS was conducted
to assess the reliability of uncommon unilateral and bilateral tasks in Study
Three. The research showed that the reliability of both tests were similar.
However, reliability was reduced in both unilateral and bilateral movements
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when light loads rather than heavy loads were lifted (ICC of unilateral FHS
with 40% and 70% of isometric maximum load were 0.70 and 0.90
respectively; ICC of bilateral FHS at 40% and 70% loads were 0.64 and 0.95
respectively). So poor reliability of unilateral tasks is unlikely to have affected
the results here. As such, the results of the present study might suggest that
early adaptations to concurrent strength and sprint/jump training are not
specific to the laterality of training exercises.
7.5.4 Velocity-specific Isokinetic Torque Changes
Adaptations to RT have also been shown specific to the velocity at which
training exercises are performed (Coyle et al., 1981; Caiozzo et al., 1981;
Wilson et al., 1993). In the present study, greater knee extension torque was
produced across all subjects at 30o.s-1 than at 180o.s-1. However there was
no general increase in torque at either movement velocity and there were no
between-group differences. Therefore, subjects who performed RT did not
show greater improvements in slow speed strength (as measured by an
isokinetic leg extension task at least) nor did subjects who trained only with
high-velocity sprint and jump movements significantly increase their high-
speed strength.
Given that the training performed by the subjects did not involve isokinetic
knee extension, the results could be attributed to poor test specificity
(Abernethy et al., 1995; Wilson et al., 1996). It is worth noting that muscles
with less pennation and shorter fibre lengths are better able to perform high-
velocity contractions (Sacks & Roy, 1982; Kumagai et al., 2000). In the
present study, pennation and fascicle length (used as a measure of fibre
length) decreased in the vastus lateralis muscle of SJ subjects. If these
changes were representative of changes in other vastii muscles, increases in
knee extension velocity could have been expected. Given no velocity-specific
isokinetic knee extension changes were seen it is possible that movement
pattern-specific training was also needed for performance changes to be
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realised. That is, the testing and training exercises might have had to be
similar. The result therefore highlights the movement pattern-specific nature
of strength adaptations. It is unlikely though that the results of the isokinetic
tests reflect an absence of absolute strength gains after training since
subjects improved their force production in many of the multi-joint resistance
tests.
Mechanisms other than architectural changes have been proposed for
velocity-specific strength gains. Neural adaptations might include increases in
muscle activation (Häkkinen & Komi, 1983, 1985, 1986; Häkkinen et al.,
1985a,b), selective activation of muscles with high fast-twitch fibre content
(Duchateau et al., 1986; Nardone & Schieppati, 1988) and increased motor
unit synchronisation (Moritani et al., 1987). Muscular changes might include
changes in myosin heavy chain (Jansson et al., 1990; Tesch et al., 1989) and
light chain expression (Jostarndt-Fogan et al., 1998; O’Brien et al., 1992),
increases in myosin ATPase activity (Essén et al., 1975) and increases in fast
tropomyosin and troponin isoforms (O’Brien et al., 1992). Given the
numerous changes that result in increases in movement-velocity, or force at a
given movement velocity, it seems likely that changes in high-speed isokinetic
knee extension, sprint or jump tests would have been seen if significant
adaptations had occurred. It therefore appears that there were few changes
other than muscle architecture.
7.5.5 Changes in Muscle Architecture
7.5.5.1 Training effects on muscle pennation and fascicle length
Muscle architecture of vastus lateralis changed in accordance with changes
that have been previously reported in the literature (Kawakami et al., 1995;
Kumagai et al., 2000). For subjects who performed RT as part of their training
program, muscle pennation increased while fascicle length decreased. For
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SJ subjects, who performed only high-velocity training, pennation
decreased while fascicle length increased. Greater pennation and shorter
fascicle lengths are reported to be prominent in muscles that regularly perform
high-force, low-velocity contractions (Burkholder et al., 1994; Van Eijden et
al., 1997) whereas muscles that participate more regularly in movements of
high velocity tend to possess smaller pennation and longer fascicle lengths
(Burkholder et al., 1994; Kumagai et al., 2000). Indeed the length of a muscle
fibre has been theoretically and experimentally shown to be related to the
fibre’s contraction velocity (Burkholder et al., 1994; Sacks & Roy, 1982;
Wickiewicz et al., 1983). Until recently however, no research had shown a
relationship between muscle architecture and the performance in complex
tasks until Kumagai et al. (2000) reported a high correlation between 100 m
sprint performance and fascicle length of leg musculature (faster sprint times
correlated with longer fibres). Furthermore, while changes in pennation have
been more extensively researched and the relationship between pennation
and physical performance highlighted (Kawakami et al., 1993, 1995), no
research has examined muscle architecture changes when both high-velocity
and high-force training has been performed concurrently.
The results of the present study suggest that high-velocity training in the
absence of low-velocity, high-force training was associated with a decrease in
pennation and increase in fascicle length. One could deduce from this that
the length of muscle fibres increased in subjects who performed only high-
velocity training (assuming muscle fibre length is synonymous with fascicle
length). Also, when RT was performed with the high-speed training (in the
present study the quantity of high-speed training was also reduced for the
weight training groups) muscle architecture changes were similar to those
seen in muscles that participate often in high-force contractions. Given this,
the muscle architecture of SJ subjects appeared to adapt to produce higher
velocity contractions. The muscle architecture of SQ and FHS subjects,
despite subjects in these groups also performing high-velocity training,
adapted to produce contractions of higher force.
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For rectus femoris, muscle architecture changes were less consistent.
Pennation increased in the distal part of the muscle in SQ and FHS subjects
compared to SJ suggesting similar changes to vastus lateralis. However no
changes were seen at the proximal site and no changes were seen in fascicle
length. The inconsistent results might be attributed to the complex functioning
of this biarticular muscle. During most multi-joint lower limb movements (eg
pushing movements), knee extension and hip flexion occur simultaneously, as
do knee flexion and hip extension. As such, even during movements where
the joint ranges of motion are large, the length of rectus femoris muscle may
change little but instead act almost isometrically to transfer force (or more
correctly joint power) from the hip to the knee (Bobbert & Ingen Schenau,
1988, 1992; Jacobs et al., 1993; Van Soest et al., 1993). Given that pushing
movements are performed frequently in sport, the training stimulus provided
to the rectus femoris may not have been sufficiently unique to promote
architectural changes.
7.5.5.2 Training effects on muscle thickness (hypertrophy)
Muscle hypertrophy is not only well correlated with strength levels in humans,
but is considered important for continued strength increases in well trained
athletes (Jones, 1992; Narici et al., 1989). Since the ability to produce power
in movements depends on both the speed and force of muscle contraction,
larger and stronger muscles may contribute to greater power production. In
the present study there was a significant increase in muscle size of rectus
femoris and vastus lateralis (as estimated by muscle thickness changes)
across all subjects. However the increase was not different between the
groups. Effect statistics suggest there were some differences in hypertrophy
among the groups, but these changes were small and inconsistent. There
was no apparent effect therefore of RT per se or the movement pattern of
training exercises on hypertrophy. Whether the five-week training phase was
too short for significant differences in hypertrophy to be seen is unclear.
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However given there were significant increases in muscle thickness over
the training period across all subjects one would have to assume that training-
related differences in hypertrophy would occur only in the long term.
It is perhaps of interest to note that muscle thickness increases were as large
for SJ as they were for FHS and SQ. Given hypertrophy is often associated
with RT, it is unclear how hypertrophy occurred in SJ. One theory is that the
hypertrophy in SJ muscles reflected the accumulation of fluid within the
muscle. The accumulation of metabolites during exercise triggers osmotic
changes that pull plasma into the muscle cells. Therefore the muscles of SJ
subjects may have become more ‘full’ as a result of their high-intensity
training. A second theory is that the training promoted increases in
sarcoplasmic material (Nikituk & Samoilov, 1990). Namely, increases in
creatine phosphate, free creatine, ATP and glycogen stores, as well as some
increase in capillarisation may have occurred (Fleck & Kraemer, 1988;
MacDougall et al., 1977). However, given the subjects often performed sprint
and jump training, and performed a four-week familiarisation, significant
increases in fluid within the muscle and greater sarcoplasmic content (an
acute exercise response) would not have been expected unless training was
of higher-than-normal intensity (a point that was discussed earlier).
Furthermore, at least four days separated the final training session and the
assessment of muscle thickness. This period would have allowed much of
the muscle volume associated with the acute exercise response to subside.
As such, it is unlikely that these two mechanisms would have been solely
responsible for the increase in muscle thickness of SJ subjects.
Another theory is that some selective hypertrophy of type II muscle fibres
occurred over the training period as training volume increased. Hypertrophy
of type II fibres has been shown to occur within weeks of beginning sprint-type
training (Mero et al., 1983; Sleivert et al., 1995). Indeed Sleivert et al. (1995)
showed that both fast- and slow-twitch fibres areas increased in a sprint-
trained group (10 s cycle sprints) similarly to a resistance-trained group in an
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eight week training regime using untrained subjects. Again however,
hypertrophy of fast-twitch fibres of the subjects in the present study could be
expected to be small given the subjects’ training history and their lack of
improvement in high-speed isokinetic knee extension.
A final theory is that, despite the pennation of vastus lateralis muscles of SJ
subjects becoming smaller after training, increases in fibre length may have
resulted in increases in muscle thickness. Increases in pennation are often
accompanied by decreases in fibre length (Benninghoff & Rollhauser, 1952;
Burkholder et al., 1994), so the opposite would also be likely. However, given
that muscle thickness is a function of muscle pennation and fibre length
(MT=FL•sinθ, where MT = muscle thickness, FL = fascicle [fibre] length and θ
= pennation), if fibre length increases were of greater proportion to pennation
reductions then an increase in fibre length would cause an increase in muscle
thickness, regardless of actual fibre hypertrophy. More likely, the hypertrophy
seen in the present study reflected a combination of adaptations. Whether the
rate of hypertrophy seen here would have continued with further training is
unclear.
7.5.5.3 Relationship between Muscle Thickness, Pennation and Fascicle
Length
Much research has investigated the relationship between muscle size
(especially muscle thickness) and pennation. While it is logical that increases
in muscle size are coupled with increases in pennation to allow more muscle
tissue to attach to a given area of tendon (Kawakami et al., 1993; Rutherford
& Jones, 1992), research has shown inconsistent results. Both cross-
sectional and longitudinal studies have investigated the relationship with some
finding a relationship (Kawakami et al., 1993, 1995, 2000) and others not
finding a relationship (Henriksson-Larsén et al., 1992; Rutherford & Jones,
1992) between the two architectural features. Therefore, correlation analysis
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was used in the present study to further assess the relationship between
the different architectural measures. There was no correlation between
muscle thickness and pennation. Therefore changes in muscle thickness
appeared not to be related to changes in pennation supporting the reports of
Henriksson-Larsén et al. (1992) and Rutherford and Jones (1992)
There was however a significant relationship between muscle pennation and
estimated fascicle length. Indeed, between 67% and 85% of the variability in
fascicle length can be attributed to changes in pennation, or vice versa. The
result is in agreement with other research showing a similar relationship
between pennation and fascicle length where longer fibres tend to attach at
smaller angles to the tendon (Burkholder et al., 1994; Henriksson-Larsén et
al., 1992; Lieber & Blevins, 1989; Sacks & Roy, 1982). Since there was no
correlation between muscle thickness and fascicle length, one may speculate
that fascicle length change occurred independently of muscle thickness.
Given however that pennation and fascicle length were highly correlated and
changed differently between the groups (decrease in pennation and increase
in fascicle length in SJ compared to SQ and FHS), the movement velocity and
force requirements of training exercises might have affected pennation and
fascicle length
7.5.6 Muscle Recruitment Pattern Changes with Training
7.5.6.1 Changes in EMG amplitude or ‘neural drive’
The recruitment timing and magnitude of agonist (Buchanan et al., 1989;
Buchanan & Lloyd, 1997; Theeuwen et al., 1994), antagonist (Buchanan et
al., 1986, 1989; Sergio & Ostry, 1995) and stabilising muscles (Oddsson &
Thorstensson, 1990) has been shown to change when forces are applied in
different directions and at different joint angles. For example, Nakazawa et al.
(1993) found that the recruitment of brachioradialis and biceps brachii
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muscles changed depending on the range of motion through which the
elbow joint moved (0-30o, 30-60o and 60-90o) and the mode of contraction
(concentric or eccentric). One might expect therefore that chronic training
could alter muscle contraction patterns (Carolan & Cafarelli, 1992; Moritani,
1992; Sale, 1992).
In the present study, changes in normalised EMG during the acceleration
phase of a sprint run were inconsistent between subjects. Generally however,
subjects who performed weight training exhibited greater gluteus maximus
(GM) activation during the recovery part of the stride cycle and greater biceps
femoris (BF), vastus lateralis (VL) and rectus femoris (RF) activation
immediately prior to foot-ground contact (see Figure 7.8). The increase in GM
activity during the recovery phase could be considered counterproductive
since hip flexion is the predominant movement in this phase. The increases
in BF, VL and RF activity possibly helped prepare for foot-ground contact. For
SJ subjects there was little change in normalised EMG throughout the stride
cycle, although a slight increase in hip flexor (HF) activity could be seen early
in the foot-ground contact phase and early in recovery (Figure 7.8). The
importance of the increase in activity in the foot-ground contact phase is
unclear, but might allow greater control of the leg during ground contact. The
increase early in recovery however seems important since one would expect
greater hip flexor force to improve the speed of leg recovery. As such, more
change can be seen in the EMG patterns of subjects who performed
resistance training. It is possible that most of these changes are
counterproductive.
For the VJ, a marked decrease in RF activity was seen early in the
descending phase followed by increases in GM activity during the transition
from descending to ascending phases (see Figure 7.9). Furthermore, there is
a marked decrease in GM EMG prior to the end of the jump. The decrease in
RF activity early might suggest a more passive beginning to the jumping
movement whereas the increase in GM activity in the transition phase and
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decrease late in the jump suggests that GM was contributing to force
earlier in the jump. Given that greater hip extension torque can be transferred
to the knee and ankle joints by the biarticular muscles (RF and
gastrocnemius) and that earlier increases in muscle activity are associated
with greater jumping performance (Bobbert et al., 1996; Voigt et al., 1995), the
change in GM activity may be beneficial to jump performance.
Few changes were observed in EMG activity of SJ subjects, although a slight
decrease in BF activity early in the transition phase and an increase in activity
during the ascending phase suggests that activation of this muscle was
altered after training (Figure 7.9). Given the biceps femoris is a hip extensor
(and knee flexor) the increase in activity during ascent may be beneficial.
Again then, greater (non-significant) changes were seen in subjects who
performed weight training, however for the VJ, the changes may have been
more productive than for the sprint run.
Given these results, it could suggested that RT influenced muscle recruitment
patterns. For weight trainers the changes may have affected their efficiency
during the acceleration phase of a sprint run, but for the VJ these changes
might have improved performance. For SJ subjects, muscle recruitment
patterns appeared not to change significantly. It appears therefore that the
provision of RT in addition to sprint and jump training may, even in training
periods of only a few weeks, influence muscle recruitment patterns. These
changes however did not significantly affect their sprint or jump test
performances. Unfortunately data were only available for ten subjects. Also
inter-subject variability was high (see 95% confidence intervals in Figures 7.5
& 7.6). Thus it was difficult to make clear conclusions about muscle
recruitment strategies. Also, longitudinal changes in EMG are difficult to
detect using surface electrodes since exact replication of the preparation and
positioning of electrodes is impossible. Nonetheless, future research may be
compared to the current research and a more clear idea of muscle contraction
changes gained.
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7.5.6.2 Muscle co-contraction and muscle activation onset changes
Some authors have suggested that movement-specific adaptations to training
are partially attributable to changes in muscle co-contraction (Weir et al.,
1994, 1995b). Certainly, antagonistic co-contraction may be modified after
training (Baratta et al., 1988; Carolan & Cafarelli, 1992). Thus, co-contraction
patterns of subjects who performed weight training could be expected to
change. However no differences were observed in co-contraction during the
acceleration phase of the sprint run in either group. Furthermore, there were
no changes in EMG onset times during the VJ. While the small sample size
and high variability of test performances may have masked significant
findings, none of the variables investigated approached statistical
significance. As such, there was no evidence that muscle co-contraction
patterns (for the sprint run) or activation onset times (for the VJ) were altered
during training. Thus it is unlikely that the training performed here was
sufficient to promote such changes. One can consider that short duration RT
has little effect on muscle contraction sequences and therefore on
performance.
7.5.7 Practical Implications
There were no performance differences between those athletes who
performed RT and those that did not. Generally all groups improved their
performance in strength and power tasks but showed no marked improvement
in sprint (except 10 m sprint time) and jump performance. Nonetheless, there
was some evidence that changes had occurred in muscle architecture and in
the nervous system. Furthermore, there was evidence of angle-specific
training changes in SQ subjects. Given that the muscle architecture of
subjects who performed resistance exercises adapted in a way thought to
produce higher force contractions, whereas muscles of SJ subjects adapted
to produce higher velocity contractions (Burkholder et al., 1994; Kawakami et
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al., 1993, 1995), it could be suggested that the incorporation of RT into a
longer training plan could have a negative impact on movement speed.
Nonetheless, power rather than pure speed is often required for successful
performance in sport. Since power production requires a combination of both
muscle force and contraction velocity, an absence of training that can
enhance muscle force could also have long-term detrimental effects.
Of interest here though was that muscle architectural changes occurred
rapidly. Data presented in this study may provide a solution to the problem of
how to use RT to improve muscle force characteristics without compromising
contraction speed (at least from a muscle architecture point of view). Strength
and speed training could be performed concurrently in a training regime. The
speed training (often representing task training) would improve the efficiency
of task performance and promote changes that improve muscle contraction
velocities while RT would improve the force of muscle contractions. Then,
several weeks from a major competition (or whatever the season’s focus) RT
could be phased out. Muscle architectural changes might then rapidly adapt
to the speed training, muscle activation patterns that may have been
compromised by RT may revert closer to optimum, and fatigue and muscle
damage synonymous with RT could be reduced. Thus optimum conditions
would exist for high-speed or powerful movements. Taper periods commonly
used by athletes would probably serve this purpose.
There was less evidence to suggest that movement pattern-specific changes
occurred in the present study with only some change in the angle at which
peak isokinetic knee extension torque was produced in SQ subjects.
Unfortunately, no comparisons could be made between SQ and FHS subjects
regarding muscle activation changes because data was only collected for a
small number of subjects. However, past evidence, and evidence from the
knee extension test in the present study, suggests that the movement pattern
of training exercises has some effect on movement efficiency (Baratta et al.,
1988) and strength expression (Kitai & Sale, 1989; Lindh, 1979; Weir et al.,
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1994; Wilson et al., 1996). If this is indeed true, then athletes should use
resistance exercises that mimic the task they wish to improve.
179
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8.1 DOCUMENTATION OF THEORY
There is much contention as to the process of neuromuscular adaptation to
RT. Commonly, neural adaptations are believed to occur prior to muscular
changes, however much evidence suggests that changes to sarcomere
length, fibre size, and muscle architecture can occur within hours or days of a
stimulus. It is therefore possible that adaptations in the nervous system are
secondary to muscular changes. That is, the nervous system adapts to the
‘new’ muscle forged by training. As such, the purpose of this chapter is to
speculate as to the process of neuromuscular adaptation to RT or concurrent
RT and speed training.
8.1.1 Are strength changes related to muscle activation?
Early changes in strength during a period of RT have traditionally been
ascribed to adaptations within the neural system (DeVries, 1968; Narici et al.,
1989; Sale, 1988). This is most likely due to research showing that early
strength changes were related to changes in muscular electrical activity (i.e.
increases in EMG) rather than changes in muscle size (e.g. Moritani, 1992;
Narici et al., 1989). It was suggested that strength increases resulted from
greater activation of muscle rather than increases in the size or number of
contractile elements. Indeed, early research using electrical muscle
stimulation suggested that, after training, those subjects who were unable to
fully activate their muscles during a contraction were able to do so after
strength training (Jones & Rutherford, 1987; Rutherford & Jones, 1986).
However more recently, the idea that untrained subjects could not fully
activate their muscles to the same degree as their strength-trained
counterparts has been questioned (Behm & St-Pierre, 1998; Cafarelli &
Fowler, 1993). While research has shown that untrained subjects could not
fully activate their muscles (Allen et al., 1995; Belanger & McComas, 1981;
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Dowling & Cardone, 1994; Lloyd et al., 1991; Strojnic, 1995) complete
muscle activation has been shown to occur in untrained subjects (Bellemare
et al., 1983; Gandevia & McKenzie, 1988; Rutherford et al., 1986).
Presenting the results of training studies, some researchers reported that
most or all subjects could fully activate their muscles prior to training
(Garfinkel & Cafarelli, 1992; Jones & Rutherford, 1987; Rutherford & Jones;
1986) and Sale et al. (1992) did not find a change in subjects’ quadriceps
activation after dynamic RT. More recently, Lyle & Rutherford (1998) and
Martin et al. (1994) showed that increases in strength occurred after
stimulation training where motor commands were not required in training.
Also, Herbert et al. (1998) showed increases in strength only occurred in
subjects who weight trained but not in subjects who performed imagined
contractions. There was also no change in muscle recruitment (estimated by
a sensitive form of the electrical stimulation technique) after training. These
studies provide further evidence that short-term changes need not result from
an increased recruitment of muscle.
Therefore, other factors might explain the increases in EMG seen with weight
training. For example Yao et al. (2000) reported that greater surface EMG
occurs concomitantly with greater motor unit synchronisation. Also, increases
in muscle mass (Alway et al., 1992; Bell & Jacobs, 1990; Hortobágyi et al.,
2000) and decreases in radial packing density (Claassen et al., 1989; Horber
et al,. 1985; Jones & Rutherford, 1987) after RT might allow more active
tissue to be located within the pick-up area of a surface electrode. Similarly,
reduced EMG signal filtering could be expected with decreases in
subcutaneous and/or intra-muscular fat that might accompany training. It is
very possible then that increases in EMG after RT do not reflect increased
muscle activation. Thus, early strength improvements might result from some
other mechanism in addition to, or exclusive of, muscle activation changes.
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8.1.2 How does muscle strength increase with resistance training?
In view of conflicting evidence as to the cause of the increase in EMG with
RT, mechanisms involving systems other than the nervous system must also
be considered. Hypertrophy is rarely suggested to be a factor in early
strength adaptation (Narici et al., 1989). This is largely because changes in
muscle thickness, cross-sectional area or volume are significant only weeks
after training onset. However it may be possible that early fibre hypertrophy
cannot be detected by anthropometric, ultrasound or magnetic resonance
imaging techniques. Needle biopsy studies have shown Increases in fibre
area within weeks of the commencement of training (Esbjörnsson-Liljedahl et
al., 1996). Furthermore, significant fibre hypertrophy (up to 30%) has been
seen in electrically-stimulated rabbit muscle after only four days. However
increases in radial packing density (Claassen et al., 1989; Horber et al,. 1985;
Jones & Rutherford, 1987) or decreases in intramuscular fat could minimise
changes in muscle cross-section or volume. Furthermore, a change in the
size and pennation of fibres in pennate muscles occurs with a decrease in
fibre length (Benninghoff & Rollhauser, 1952; Muhl, 1982). Such adaptations
would minimise muscle volume changes to allow the muscle to better fit within
its compartment (Benninghoff & Rollhauser, 1952; Burkholder et al., 1994).
Thus, muscle size changes might not be readily detected by ultrasound or
MRI techniques. However the dismissal of muscle hypertrophy as a factor
involved in strength increases with RT is perhaps unwarranted.
Muscle architecture is hypothesised to affect muscle function in that larger
angles of pennation and shorter muscle fibres are beneficial to higher-force
contractions (Burkholder et al., 1994; Kumagai et al., 2000; Sacks & Roy,
1982; Van Eijden et al., 1997; Wickiewicz et al., 1984). While fibre lengths
have been shown to change rapidly, no studies have thoroughly examined the
time course of pennation changes. Certainly however, such changes occur
within weeks (Henriksson-Larsén et al., 1992). The results of the present
thesis also suggest this. Some authors hypothesise that increases in
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pennation are a response to muscle hypertrophy allowing more contractile
tissue to attach to a given area of tendon (Kawakami et al., 1993; Rutherford
& Jones, 1992). However poor relationships between muscle size (thickness
or fibre area) and pennation have been shown (Blazevich & Giorgi, 2001;
Blazevich et al., 1998; Henriksson-Larsén et al., 1992; present thesis). Also,
Rutherford and Jones (1992 [longitudinal study]) found no relationship
between changes in muscle size and changes in pennation, and no
relationship was seen between the two in the present thesis. So pennation
changes do not seem to mirror changes in muscle hypertrophy.
8.1.3 How would muscle architecture affect strength?
In Study Five of this thesis all training groups showed similar increases in
muscle size, although only the groups that performed RT showed greater
pennation of the vastus lateralis. This suggests perhaps that the stimulus
provided by RT influenced pennation changes. Theoretically this makes
sense. The muscle length change of highly-pennate muscle is greater for a
given length of fibre shortening since fibres not only shorten during
contraction, but rotate. So sarcomeres in a pennate muscle could probably
work closer to their optimum lengths during a dynamic contraction (Muhl,
1982). There is good theoretical evidence therefore that pennation should
increase in response to high-load training even before hypertrophy occurs.
The shorter fibres in muscles with greater pennation might point to another
mechanism by which strength can be improved. Force from sarcomere
shortening is transmitted through all of the serially-arranged sarcomeres
within a fibre. Thus, force produced by the contracting fibre can only be as
great as the weakest sarcomeres. Indeed, when force produced by one
sarcomere has to be transmitted through other sarcomeres, energy will be lost
at each sarcomere. Thus, fibre contraction force could be greatest when only
a small number of sarcomeres are arranged in series. Improved force
production however would be attained from many parallel columns of
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sarcomere strings.
Moreover, shorter fibres tend to possess longer sarcomeres. The longer
sarcomeres would have longer actin and myosin filaments. Assuming all
fibres of a given species of animal have a similar number of cross-bridges per
unit length of filaments, and similar likelihood for cycling of cross-bridges,
longer sarcomeres would have more actin-myosin attachments and provide
greater contractile force. So decreases in fibre length (and increases in
sarcomere length) would benefit high force production by allowing more
cross-bridges per sarcomere to produce force.
Early losses of sarcomeres in series could also minimise the energy cost of
muscle hypertrophy if it mirrored increases in sarcomeres arranged in parallel.
The energy saved, or absorbed, by sarcomere loss could be used to build
more sarcomeres in series. Therefore, early increases in fibre area would be
cost-effective. Longer-term hypertrophy that involves increases in
sarcomeres arranged in parallel, with no further decreases in sarcomeres
arranged in series would only occur if the stimulus for strength increases were
chronic. Therefore, muscles with both greater pennation and shorter fibres
may be better for contractions involving high forces.
8.1.4 Is there a neural explanation for angle-specific strength changes?
Adaptations to strength training have been shown to be highly specific
(Abernethy & Jürimäe, 1994; Lindh, 1979; Rutherford et al., 1986; Thépaut-
Mathieu et al., 1988; Weir et al., 1995a). Therefore, strength gained by the
performance of one task does not necessarily translate to strength in another
task. Most clearly, strength adaptations are specific to the joint angle (or
muscle length) at which training is performed (Kitai & Sale, 1989; Weir et al.,
1994). No single mechanism has been proven responsible for the angle-
specific adaptations reported by such investigators. Kitai and Sale (1989)
suggested that neural mechanisms were likely since angle-specific
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plantarflexor strength changes were seen in voluntary but not stimulated
contractions. However many studies have not shown changes in muscle
activation after RT (Brown et al., 1990; Carolan & Cafarelli, 1992; Harridge et
al., 1999; Herbert et al., 1998; Sale et al., 1992). The lack of changes is
perhaps due to muscle activation being nearly maximal in most subjects
(Carolan & Cafarelli, 1992; Garfinkel & Cafarelli, 1992). It has also been
suggested that such techniques are not sensitive enough to detect small
changes in muscle recruitment (Allen et al., 1995; Gandevia et al., 1995).
Further evidence for a neural explanation for angle specificity was provided by
Weir et al. (1994) who showed angle-specific changes in both a trained and
untrained limb. They hypothesised that strength increases seen in the
untrained limb indicated that neural mechanisms were involved. However
Srihari (1981) reported changes in myosin light chain expression of the soleus
muscle in a control limb after cross-innervation of soleus with gastrocnemius.
Therefore muscular changes can occur in a control limb, even in the absence
of training or learning. Thus cross-education may not be evidence for a
neural explanation for angle-specific strength changes.
Other studies have also not shown changes in surface EMG with angle-
specific strength changes (Weir et al., 1994, 1995b). Further, angle-specific
torque changes have been shown with electrical muscle stimulation training
where central motor commands are not required (Martin et al., 1994). Despite
neural mechanisms being held most likely responsible for angle-specific
strength changes, no research has definitively shown this to be the case.
Therefore, adaptations that do not involve changes in the nervous system
resulting from the learning process might be involved in the angle-specific
strength adaptations seen with resistance training.
8.1.5 How could muscle strength increase in an angle-specific manner?
Sarcomere length has been shown to change not only in response to periods
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of immobilisation at lengths greater or lesser than rest length (Tabary et al.,
1972; Goldspink et al., 1974; Heslinga et al., 1995) but also in response to
imposed stretch (Williams, 1990), stretch combined with electrical stimulation
(Williams et al., 1986) and downhill running (Lynn & Morgan, 1994).
Therefore, sarcomere adaptation may occur in response to an imposed load.
Herring et al. (1984) found that masticatory muscles’ optimum length for force
production was most related to the length at which maximum force was
required in vivo. Thus, sarcomere length might adapt to a new length should
resistance-type training be performed at a given muscle length. This could
explain the angle-specific strength adaptations shown in some studies (see
Koh, 1995).
Sarcomere length affects the active length-tension relationship of muscle.
Although elastic and viscous properties of a muscle affect its length-force
relationship (Gillard et al., 2000), active muscle force is usually greatest near
the length of optimum filament (actin-myosin) overlap. A slight change in the
length of optimum overlap would alter the length at which the fibre produces
optimum force. However, in pennate muscles, length-tension properties are
more complex. The force produced along the length of a tendon is reduced
as the angle at which fibres attach to the tendon is increased (Burkholder et
al., 1994; Wottiez et al., 1983). In pennate muscles, muscle shortening is
caused not only by fibre shortening, but also by rotation of those fibres (Muhl,
1982). As such, the angle of fibres to the tendon increases as the muscle
shortens and the proportion of fibre force acting along the tendon is reduced.
The greater the pennation of a muscle, the earlier in a contraction fibre
rotation becomes significant and force declines. Therefore, a muscle’s length-
tension characteristics are influenced, among other things, by both the length-
tension characteristics of its constituent fibres the angle they attach to the
tendon (or aponeurosis).
While the length of sarcomeres influences the properties of a muscle,
sarcomere length is heterogeneous throughout the muscle (Scott et al., 1993;
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Van Eijden & Raadsheer, 1992; Willems & Huijing, 1994). Therefore, for a
given shortening of muscle, some fibres will shorten more than others (Weijs
& Van der Wielen-Drent, 1983; Van Eijden & Raadsheer, 1992). It would be
more efficient perhaps for motor units at near-optimum lengths to contract in
most contractions while those on their descending limb could lengthen to
provide passive force and improve force transmission through the muscle
fibres.
Indeed motor units of some longer muscles are not randomly distributed
throughout a muscle and are not equally likely to be recruited, but are
grouped as sub-populations or ‘functional compartments’ based on the
likelihood of their activation during a given contraction (Segal, 1992). For
example, the biceps brachii appears to contain a group of motor units that are
readily recruited during arm flexion but a separate group that are readily
recruited during forearm supination (Ter Haar Romeny et al., 1982; 1984;
Theeuwen et al., 1994; Van Zuylen et al., 1988). Such compartmentalisation
has also been shown in muscles such as the human masseter (Tonndorf &
Hannam, 1994) and cat lateral gastrocnemius (English & Weeks, 1984).
Further evidence that selective activation of compartments can increase the
number of sarcomeres in a region of muscle has been provided by studies
showing selective hypertrophy of certain regions of muscle. Narici et al.
(1989) found that hypertrophy of the quadriceps was greater in vastus
medialis and vastus intermedius than rectus femoris and vastus lateralis after
isokinetic strength training. Furthermore, Housh et al. (1992) reported
significant increases in vastus lateralis and vastus intermedius cross-sectional
area at the mid-level and in rectus femoris across the entire muscle following
isokinetic strength training. In the present study, there was evidence that
hypertrophy of parts of vastus lateralis and rectus femoris differed depending
on the training performed by subjects.
Therefore, continued selective recruitment of muscles and sections of
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muscles may result in selective hypertrophy of these regions. Given that
muscle hypertrophy is at least partly attributable to increases in the number of
sarcomeres (Alway et al., 1989; Gollnick et al., 1981; McDonnagh & Davies,
1984), increases in the number of those sarcomeres at optimum length might
occur in certain regions of muscle with RT. Therefore, the recruitment of
motor units within a muscle seems not only contingent on the ‘size principle’
(Milner-Brown et al., 1973), type of contraction (Person & Kudina, 1970) and
sensory input (Garnett & Stephens, 1981; Grimby & Hannerz, 1974;
Romanguére et al., 1992) but on their spatial location within the muscle.
It is likely then that the recruitment of functional compartments is related to the
length of sarcomeres in the muscle fibres. Van Zuylen et al. (1988) found that
the recruitment of these compartments was dependent on the joint angle, and
therefore the muscle length, at which a contraction was performed. Indeed,
Herring et al. (1984) found that sarcomere lengths varied between different
locations in the pig medial pterygoid, masseter and temporalis muscles. It is
therefore possible that functional compartments are organised on the basis of
the length-tension relationships of a fibre’s constituent sarcomeres. Strength
training using a particular movement pattern or joint angle could stimulate
changes in sarcomere length within the functional compartment which was
most readily recruited for a given contraction. However, if changes also
occurred in those functional compartments that were not readily recruited,
sarcomeres in these latter compartments would then be of more similar length
at rest to those compartments that were readily recruited during the
contraction. They could therefore contribute more to subsequent
contractions. The increased muscle activity in these regions could result in
greater EMG during a given contraction at all contraction strengths since more
fibres would be recruited at low levels of force and the firing rates at
subsequently greater contraction strengths would be higher. However these
increases would only be seen if a surface electrode was placed close to the
site of increased muscle activation. The areas over which functional
compartments span would possibly also change since some compartments
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may become homonymous with others.
8.1.6 How does muscle strength increase in a velocity-specific manner?
Most increases in movement velocity have been attributed to increases in
fast-twitch fibre size or content. This makes intuitive sense since fast-twitch
fibres have higher contraction velocities than slow-twitch fibres. However,
other muscle properties can affect its velocity characteristics. Longer fibres
have been theoretically and experimentally shown to exhibit greater
shortening velocities (Burkholder et al., 1994; Sacks & Roy, 1982; Wickiewicz
et al., 1984). Furthermore, longer fibres are prevalent in fibres that often
perform higher-velocity, low-force contractions (Van Eijden et al., 1997), and
in muscles of well-trained sprint athletes (Kumagai et al., 2000). Fibre
lengthening occurs by an increase in the number, but decrease in the length
of sarcomeres (Matano et al., 1994; Williams, 1990). While it is unclear how
quickly these changes proceed in humans, they have been shown within
hours of a stretch stimulus in animals (Williams, 1990). In the present thesis
fibre length changes occurred within weeks.
The total length change of a contracting fibre equals the sum of shortening of
individual sarcomeres. Therefore, the more sarcomeres arranged in series,
the greater propensity for fibre length change. Since velocity is determined by
the length change per unit time, small displacements in each sarcomere
would culminate in large fibre length changes in a given amount of time. Thus
shortening velocity would be great. In addition, sarcomeres could shorten
less, and maintain lengths around optimum more often, if more are arranged
in series. Thus the force involved would be increased and power (dictated by
both the force and velocity of the contraction) would be greater.
8.1.7 What about conflicts in architecture and fibre type?
While fibre type changes should parallel architecture changes this is not often
190
the case. For example, the gastrocnemius muscle is characterised by large
pennation angles, short fibres and a high fast-twitch fibre percentage.
Furthermore, Burkholder et al. (1994) found a poor correlation between fibre
length and slow-twitch fibre percentage in human muscles. Why is it that a
muscle can have architecture conducive to slow-velocity, high force
production, but fibre type preponderance consistent with muscles that
produce fast force?
Perhaps fibre type is dependent more on metabolic and velocity constraints
whereas architecture is dependent more on force requirements. Fast-twitch
fibre content is highly correlated with performance in tasks requiring fast force
production (Coyle et al., 1979; Froese & Houston, 1985; Suter et al., 1993).
Their shorter half-relaxation times might also be a benefit in rapid eccentric
contractions where sarcomere elongation is required. Finally, they have a
better anaerobic capacity than slow-twitch fibres. The gastrocnemius is often
used in jumping movements where high forces are necessary, but small
amplitude rapid movements are required. Furthermore, the highly anaerobic
nature of fast-twitch fibres are useful given the muscle rarely participates in
endurance-type exercise. As an added benefit, the improved anaerobic
capacity of fast-twitch fibres might be more important in pennate muscles
where higher intra-muscular pressures could impede blood flow (Van
Leeuwen & Spoor, 1994). Increases in pennation however are usually
proportional to increases in the force production of a muscle (Benninghoff &
Rollhauser, 1952; Wottiez et al., 1983) or inversely related to fibre length
(Burkholder et al., 1994). Also, strength increases seem related to changes in
pennation, but not necessarily hypertrophy (Blazevich & Giorgi, 2001;
Blazevich et al., 1998; Henriksson-Larsén et al., 1992). So the relationship
between muscle pennation, fibre length and fibre type is complex and
probably determined by the force, velocity and metabolic requirements of a
muscle.
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8.1.8 Conclusion
The purpose of this section of the thesis was to provide evidence for the
hypothesis that changes at the muscle level, or within some regions of
muscle, can result in increases in strength without noticeable increases in
muscle activation or muscle size. Should changes in sarcomere length occur
with RT, adaptations to strength would include specific increases in strength
at the joint angle at which maximum force was exerted during training and
therefore predicts that strength increases should be task specific.
8.2 ‘PERIPHERAL ADAPTATIONS’ EXAMPLE OF STRENGTH CHANGES
AFTER RESISTANCE EXERCISE.
Any model used to explain neuromuscular changes to training (particularly
resistance training in this instance) must predict several outcomes. These
include the following:
1. Muscle activation changes should increase with strength changes,
although, since this does not occur in many cases, strength increases
should not be dependent on increases in muscle activation.
2. Strength increases must be obtainable without a marked increased in
twitch or tetanic force (i.e. level of muscle activation).
3. Early increases in muscle size should not be detectable by ultrasound or
MRI techniques.
4. Changes in strength must be specific to the muscle lengths or joint angles
used in training.
5. Angle-specific strength improvements should not occur with a decrease in
force at non-training angles, but rather little or no increase at those angles.
6. Changes in strength must be specific to the body position or posture used
in training.
7. Changes in strength must be specific to the velocity of the training
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exercises without changes in muscle activation.
8. Significant cross-education effects must be possible after unilateral
training.
9. Large increases in strength must be obtainable within the first few weeks
of training, but smaller increases should be seen thereafter.
In order to explain such an adaptive process, a fictional muscle (FM) will be
chosen as the subject of the model. It will be unipennate and able to perform
two functions, flexion and rotation. It will have a proportion of motor units
(MU’s) that are recruited mostly for flexion tasks (medial portion) and others
recruited mostly for rotation (lateral portion). Muscle fibres that are central will
tend to be activated easily during both tasks, but are not recruited for low level
force production. Thus FM is similar in function to the biceps brachii (Ter Haar
Romeny et al., 1984). 60% of its fibres will be fast-twitch and 40% slow
twitch. Furthermore, its original position of greatest strength will be with a
joint angle of 90o. Flexor training of the right limb will be performed at a slow
(15o.s-1) velocity through the range of 0o – 60o (full range of motion = 0o to
1700) of elbow flexion three times a week for eight weeks. Long rest periods
will separate three sets of 6 repetitions of exercise training.
8.2.1 What adaptations are likely in the first week of training?
Sarcomeres seem to adapt such that optimum overlap exists at muscle
lengths where high forces are commonly produced. Based on the evidence
presented previously, one might expect that an increase in sarcomere number
and decrease in length would occur with the process beginning after the first
session and predominate early in the training weeks. Consequently there
would be a change in the functional length-tension characteristics of FM
fibres. Since sarcomere lengths are not uniform throughout the muscle one
might also expect that fibres would adapt such that more sarcomeres with
ideal length-tension characteristics for the exercises are available within the
muscle. However, those sarcomeres near optimum length for elbow flexion
193
through this range of motion would have been most maximally recruited.
Even during maximal contractions sarcomeres at extreme (short or long)
muscle lengths would contribute little to the overall muscle force. Indeed
fibres on their descending limb would probably lengthen maximally and
provide passive tension and aid force transmission.
Therefore, it would most likely be that sarcomeres that were close to optimum
length when working through the training range of motion (in this example
these would probably be the centrally-located motor units that are active
during both low-level rotation and flexion) would adapt first. This would occur
with no change in neural pathways initially, however the body might soon
adapt to the new distribution of fibres with changes to the innervation of
muscle. Consequently, the number of motor units activated during low-force
flexion contractions would increase and, approaching maximum, the firing rate
of those motor units would be greater given their early recruitment. In this
case, the change in the number of fibres that are at an ideal length would
increase and be reflected in greater EMG detected at surface electrodes.
However, since only a small portion of closely-grouped MU’s would have
greater activity, changes in EMG would be small, and probably not detected
unless the electrode/s was/were placed immediately over the MU group.
If the theory previously presented is true then in multifunctional muscles the
area over which motor units are readily recruited during the task being trained
should increase if the other training is not being performed concurrently.
Indeed, Tonndorf and Hannam (1994) found some motor unit territories
crossed the intramuscular tendons that typically separated functional
compartments within the human masseter. Does this provide evidence that
motor unit territories were expanding? The model also predicts of course that
training while the muscle is in a lengthened position will culminate in fibre
length-tension changes that are ideal for working at long lengths, especially in
those motor units which are most readily recruited.
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Similarly, the theory also explains why increases in EMG are not always
seen after periods of strength training. Since only some areas of muscle will
contain sarcomeres at, or near, optimum length for a given contraction, other
sarcomeres must be either too short or too long. Sarcomeres that are too
long are said to be on the ‘descending limb’ of their length-force curve.
Research by Morgan (1990; although tentatively refuted by Allinger et al.
[1996]) has shown that such sarcomeres might lengthen to their physiological
maximum. At this length they provide only passive tension created by their
elastic structures. There would be no requirement for activation of these
sarcomeres. Thus EMG electrodes placed on the muscle around areas
where sarcomeres tended to their physiological maximum may not record
signals that represent total muscle activity. Thus one difference between
those studies that showed increases in EMG after training and those that did
not may be the positioning of electrodes over the muscle. Multiple electrode
arrays (see Chanaud et al., 1991; Thusneyapan & Zahalak, 1989) may
therefore be more useful in gauging muscle activity changes after training.
It is possible also that hypertrophy of fibres (increases in contractile and
connective tissues) that are most active would occur rapidly. This might
parallel decreases in intra-muscular fat deposits and increases in the radial
packing density of contractile tissue. As such, increases in overall muscle
thickness, cross-section or volume would not be seen. Furthermore, early
hypertrophy might be confined only to those areas where sarcomeres are
near optimum length. Selective hypertrophy has been shown after RT (Housh
et al., 1992; Narici et al., 1996) and there was good evidence that it may have
occurred in Study Five of the present thesis. Nonetheless, if as presented
above joint-angle specific changes occur largely by sarcomere length
changes one could speculate that not only would a muscle become stronger
at one muscle length, but weaker at another. A more general hypertrophy of
the muscle would prevent such a decline at non-training angles.
Due to its unipennate fibre arrangement, increases in pennation would
195
contribute to strength increases in FM. It is possible that pennate muscles
have a greater propensity for early strength increases since increases in
pennation could occur simultaneously with other changes. Alternatively, the
increased pennation of such muscles might occur in place of other
adaptations. The increase in force production capability of pennate muscles
would then be the same as for parallel muscles. Fibre lengths would also
decrease, firstly because fibre shortening would reduce the volume of the
muscle after pennation had increased, thus allowing the muscle to remain a
size that easily fits into the compartment in which it sits. Also the decrease in
fibre length would increase force-generating capacity. The slow contractions
might induce some changes in fibre type, but since the muscle is rarely
performing contractions in an ischaemic state (i.e. many contractions at high
force with minimal rest) fibre type transition from its current proportions would
be unlikely.
Increases in the left (non-trained) FM might also occur. Generally, cross-
education has been attributed to neural causes. However changes at the
muscle level might occur. Srihari (1981) showed that myosin light chain
expression changed in a soleus muscle after cross-innervation of the
contralateral soleus with gastrocnemius. It was hypothesised that a neural
feedback mechanism was involved in this muscular adaptation. However it is
possible that, since messengers (namely hormones) stimulate protein
synthesis, a blood-borne messenger is responsible. Indeed increases in
blood flow to a non-training limb have been shown after unilateral training
(Yasuda & Miyamura, 1983). What if training of one muscle stimulated the
release of these messengers into the bloodstream? If these messengers
attached to particular receptors that differed between muscles, or differed
between sections of muscles, then muscular changes could occur without
intervention from the nervous system. Such a mechanism is purely
speculation, changes in muscle architecture of fibre properties have not been
investigated after unilateral training. The cause of the cross-education effect
therefore is unclear.
196
It must be added however that some early neural adaptations could occur.
Increases in synchronisation might enhance force production. Early changes
could at least partially explain the increase in surface EMG shown in some
studies (Yao et al., 2000). Also, a decrease in reflex inhibition in the first two
weeks of training would allow more motor units to contribute to force under
high loads. A reduced reflex inhibition however is most likely to be significant
in ‘untrained’ as apposed to ‘active’ or ‘well-trained’ subjects whose
neuromuscular systems would have experience in lifting heavy loads.
Nonetheless, early strength increases do not have to be mediated by a
‘reworking’ of neural pathways initially, but by muscular changes which occur
in response to the stresses placed on them.
8.2.2 What about muscle activation?
It is interesting to hypothesise why we often do not see a change in muscle
activation after training. First, studies which have examined sub-populations
of motor units (i.e. functional compartments) have reported some motor units
which are not activated during some tasks at low force levels (Ter Haar
Romeny et al., 1982, 1984; Van Zuylen et al., 1988). What if this is caused by
an inhibitory mechanism at the muscle level that could be controlled by neural
circuitry of the central nervous system. In this case, if muscle stimulation
could not activate these motor units during a maximum contraction, then
subjects may not be activating their muscles fully but muscle stimulation
would not allow any additional recruitment.
Should this be correct, increases in force after stimulation would be ascribed
to subjects not providing maximum effort prior to stimulation or subjects
learning how to involve all possible muscles for that specific task. After task
training, the number of motor units containing fibres of ideal length for that
contraction would increase. The inhibitory mechanism at the muscle level
would then be switched off to allow those extra motor units to be recruited
197
early. There may still be other motor units that cannot be activated.
Therefore, even though more of the muscle can be activated during a given
contraction. Electrical stimulation still might not recruit any more muscle than
is already activated during the voluntary contraction unless the subject failed
to attain maximum effort or they had not learned to produce maximum force.
Or perhaps those extra motor units are unable to significantly increase the
force of contraction since they are not near optimum length. Therefore, after
training the muscle force will improve and muscle activity would increase, but
muscle stimulation will only produce greater gains in force if the subject was
not providing a maximal contraction prior to stimulation. Again, this is purely
speculation.
Alternatively, the failure of electrical stimulation techniques to increase muscle
force might be related to the length of sarcomeres during maximal
contractions. As described earlier, sarcomeres that are at longer-than-
optimum lengthen further to their physiological maximum and exert passive
force during maximal muscle contractions. The provision of electrical
impulses to the muscle may still not allow these sarcomeres to contract since
their actin-myosin overlap would not allow sufficient force to be produced.
Those sarcomeres that are at, or are less than, optimum may always be more
readily recruited. Thus increases in muscle force with training may occur
when fewer sarcomeres lengthen to their physiological maximum, or when the
sarcomeres at or near optimum increase their force generating capacity. The
response to resistance training, particularly angle-specific adaptations to
resistance training, may reflect the number of sarcomeres at or near optimum
for a movement of given characteristics.
8.2.3 What about general strength increases?
Since adaptations to the sarcomeres, and therefore the muscle
compartments, is specific to the training task, increases in strength will not be
likely in an unassociated task. This is generally shown in past studies
198
(Abernethy & Jürimäe, 1994; Lindh, 1979; Rutherford et al., 1986; Thépaut-
Mathieu et al., 1988; Weir et al., 1995b). Unfortunately, no research has
examined the activation of compartments during maximal contractions to
determine if compartments that remain inactive during a particular task
become active at maximum.
8.2.4 Long-term adaptations?
Several processes could mediate longer-term improvements in strength.
First, the working muscle will be better able to cope with the loads imposed on
it such that eventually muscle damage and breakdown are of smaller
magnitude and protein synthesis can more dramatically outweigh it. As such,
increases in muscle size would be more rapid. This greater muscle
hypertrophy would lead to improved muscle strength. Also, the nervous
system would continue to adapt to the ‘new’ muscle state acquired from
training. Inter- and intra-muscular coordination would be enhanced so that
certain muscles within a group would be recruited before others thus
amplifying both angle-specific and body position- or posture-specific training
adaptations. Indeed one would ‘learn’ how to most effectively use the muscle
that has changed since training began. Importantly, by providing the muscle
with several stimuli (i.e. concurrent training) the adaptive process would be
more complex and clear changes would not be as readily seen. Such a result
was clearly observed in the present thesis. The processes outlined above
can be summarised as in Figure 8.1.
8.3 SUMMARY
Changes in neural pathways may not adequately predict early increases in
strength with RT. However many adaptations within the muscular system can
account for research observations well. These include changes in sarcomere
lengths and number, architectural changes and fibre hypertrophy (without total
muscle size increases). Neural adaptations may be secondary to these
199
muscular changes while long-term strength changes might be a result of
continued hypertrophy and more minor neural adaptations.
Visible hypertrophy
Fibre hypertrophyPennation & fibre length
Sarcomere adaptation
Inter- and intra-muscular coordination
Synchronisation/inhibitory reflex
0 1 2 3 4 5 6 7 8
Week of Training
0 1 2 3 4 5 6 7 8
Week of Training
50
10
0%
Rat
e of
Cha
nge
Rel
ativ
eto
Max
imum
50
10
0%
A
BFigure 8.1. Hypothesised time course of muscular (A) and neural (B) changes with resistance exercise.Many of the early changes (<2 weeks) might result from muscular adaptations with changes in thenervous system promptly following. Long-term (>6 weeks) adaptations might occur from considerablehypertrophy and continuing neural adaptation. Different muscles (i.e. different size, architecture, action,etc.) would respond differently, the model presented here is theoretical and may not be faithful to the timecourse f change.
B
A
200
CCHHAAPPTTEERR 99:: TTHHEESSIISS
SSUUMMMMAARRYY
201
9.1 SUMMARY
The first study examined the movement patterns of several resistance and
performance tasks in order to describe similarities between them. The results
were that the VJ without arm swing (particularly with arms placed across the
chest) was kinematically similar to the jump squat exercises. The traditional,
slower squat lift however was not similar largely because joint angle changes
occurred simultaneously rather than sequentially. Also, none of the broad
jump variations were similar to the FHS. Nonetheless the acceleration phase
of sprint running, as described by Jacobs and Ingen Schenau (1992) did
appear similar in both the magnitude and timing of joint angle changes to the
FHS. Given that the FHS is performed in a semi-prone position and can be
performed unilaterally, one could consider the pushing phases of these two
movements very similar. A kinematic study investigating the movement
patterns of subjects performing both tasks is required to more clearly establish
their similarity.
Although two groups of tasks (VJ with arms across the chest and jump-squat,
and the FHS and acceleration phase of a sprint run) were found to be
kinematically similar, it was unclear if they could be described as functionally
(kinetically) similar. That is, do subjects who perform well in a resistance task
also perform well in its related performance task? It is possible that for
optimum improvements in a performance task to occur, the resistance task
might have to be both kinematically and functionally similar. Results of Study
Four included a strong relationship existed between ISQ and VJ performance,
but not JSQ and VJ performance. This suggested that JSQ, while being
kinematically similar, was not functionally similar. The similarity between ISQ
and VJ may reflect their requirement for high muscle forces/stiffness at long
muscle lengths. In the VJ, high muscle forces/stiffness may be required for
optimum use of the stretch-shorten cycle. There was however a strong
relationship between the FHS and acceleration phase of a sprint run.
Furthermore, component analysis hinted at a similarity in their force-velocity
202
characteristics. As such the FHS and sprint tasks could be considered
both kinematically and functionally similar. Given the results of this fourth
study, it was deemed possible to test the effects of kinematic and functional
similarity on performance adaptations in the third study.
The purpose of the fifth study was to examine changes in SQ, FHS, sprint and
VJ performance after a short period of either concurrent resistance- and
sprint/jump training or sprint/jump training alone. Further, the effect of
movement pattern of RT exercises could be compared by two of the
resistance groups performing tasks with different movement patterns as their
dominant training exercise. After five weeks of training there was no
difference between the groups in squat, FHS, sprint or VJ performance.
Therefore, short duration, concurrent training appeared to have no significant
movement pattern- or velocity-specific effects in well-trained subjects. It was
also not possible therefore to determine if only kinematic similarity, or both
kinematic and functional similarity, was required between resistance and
performance tasks for optimum improvements in a task to occur. The low
statistical power resulting from low subject numbers may have affected
significant findings. However, if clear differences existed between groups,
these would have likely been detected since statistically significant
improvements in many of the resistance and task tests were found across the
groups after the five weeks of training.
Many factors affect the movement pattern-specific effect. Three of these were
examined in this fifth study: body position, joint angle and laterality. There
was no apparent effect of body position on training adaptations as there was
no difference between the resistance groups in their performance of the FHS
and squat tests. Although the magnitude and timing of joint angle changes
and laterality also differed between these two tasks, one would expect that if
body position affected performance then some differences between groups
would have been found given they trained with exercises that had different
body positions. On the other hand, a difference between the groups would
203
not have been conclusive evidence of an effect of body position given the
other factors that differed between the tasks.
With respect to joint angle changes, while the timing and magnitude of joint
angle changes differed between the SQ and FHS tasks, there were no
differences between the groups that trained with these tasks. Nonetheless,
there was some evidence (supported by high effect sizes) of between-group
differences in the angle at which peak torque was produced (APT) during slow
isokinetic knee extension. APT in subjects who performed SQ training was
produced at a more closed angle after training while there was no difference
in the angle for subjects who trained with the FHS. Given that the range of
motion through which the knee moved was greater for subjects who
performed the SQ training, the result provides some evidence for angle-
specific torque changes. If small changes in APT did occur between groups,
between-group differences in dynamic tests could possibly be expected after
longer training periods.
Effects of laterality of training were also investigated. There was no evidence
for laterality-specific adaptations as there were no differences in unilateral VJ,
unilateral FHS or unilateral isokinetic knee extension performance after
training. Again, the result might be due to the short training period and/or low
subject number. Alternatively the result might suggest that early adaptations
to concurrent strength and sprint/jump training are not specific to the laterality
of training exercises.
The effects of training velocity could be examined since one group performed
no RT and therefore performed only high-speed running and jumping
movements. There was strong evidence that muscle pennation of the vastus
lateralis muscle increased while fascicle length decreased in groups who
performed RT in addition to the sprint/jump training. Subjects who performed
no RT however showed no increase in pennation but longer fascicle lengths.
Such changes may have contributed to similar increases in muscle thickness
204
after training. The changes were certainly similar to those described
previously in the literature (Burkholder et al., 1994; Kawakami et al., 1995).
Nonetheless, these architectural changes, while theoretically important to the
shortening velocity of the muscle, did not manifest themselves by changes in
dynamic performance in this short-term study. There was no difference
between groups in the performance of the SQ, FHS, sprint or jump tests, nor
was there a difference in their improvements in isokinetic knee extensor
torque at any movement speed (30o.s-1 or 180o.s-1). The lack of significant
change in the knee extension test might be due to the training and testing
modes being different. However, the change in architectural characteristics of
muscle suggest that long-term training, even when resistance- and task
training are performed concurrently, might result in velocity-specific
performance changes. Given that changes occur rapidly however, athletes
who use resistance- and task training concurrently might be able to quickly
reverse any adverse architectural changes by performing only sprint-type
training.
Finally, the results of the EMG analyses were equivocal due to high inter-
individual variability and low statistical power. There was some evidence
however that changes in muscle activity of resistance-trained subjects may
have affected sprint running but improved VJ efficiency. However there was
no change in muscle co-contraction patterns in sprint running or in the muscle
activity onset times during VJ. There were also no changes in the muscle
activity patterns of sprint/jump subjects. As such, changes in the nervous
system may be highly individual, especially when resistance- and task training
are performed concurrently by well-trained subjects for short periods and
changes in the nervous system resulting from training may not be as
consistent as when RT is performed in isolation.
In conclusion, for the subjects tested here there was some evidence of
muscle architectural changes related to the velocity of training exercises.
However there were no differences between the groups in their performance
205
of SQ, FHS, sprint or VJ tests, and little or no change in joint angle-specific
torque at the knee or muscle activity patterns. Therefore, for short training
periods, changes resulting from concurrent training appear different to those
where RT is performed in isolation in that changes are not as abrupt or
consistent across subjects. Nonetheless, there is enough evidence to
suggest that differences between ‘specific’ and ‘non-specific’ training may be
significant after longer training periods.
9.2 FUTURE RESEARCH
There are many neuromuscular adaptations that can occur with RT and with
concurrent training. Certainly there is still much work needed to ascertain the
exact nature of these adaptations. This work been highlighted throughout the
thesis and will not be reiterated here. Some important research that must be
conducted however stems from limitations of Study Five. Namely:
1) changes in muscle activation need to be examined in greater detail,
2) more subjects are required to provide a more detailed and accurate
account of neuromuscular and performance changes,
3) training should be performed for longer (> 3 months) periods to allow
examination of both short- and long-term adaptations to the training.
4) Different concurrent training regimes need to be used in studies to assess
the effects of relative volumes and intensities of resistance- and task
training.
Such research, combined with more detailed research investigating singular
mechanisms would improve our knowledge of adaptations to concurrent
resistance- and speed training and help coaches and athletes plan their
training for optimum performance.
206
RREEFFEERREENNCCEESS
207
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339. Srihari, T., Seedorf, U. & Pette, D. (1981). Ipsi- and contralateralchanges in rabbit soleus myosins by cross-innervation. European Journalof Physiology, 390(3): 246-249.
340. Staron, R.S, Karapondo, D.L., Kraemer, W.J., Fry, C.C., Gordon, S.E.,Falkel, J.E., Hagerman, F.C. & Hikida, R.S. (1994). Skeletal muscleadaptations during early phase of heavy-resistance training in men andwomen. Journal of Applied Physiology, 76: 1247-1255.
341. Staron, R.S., Malicky, E.S., Leonardi, M.J., Falkel, J.E., Hagerman,F.C. & Dudley, G.A. (1990). Muscle hypertrophy and fast fiber typeconversions in heavy resistance-trained women. European Journal ofApplied Physiology and Occupational Physiology, 60(1): 71-79.
342. Steele, J.R. & Brown, J.M.M. (1999). Effects of chronic anteriorcruciate ligament deficiency on muscle activation patterns during an abruptdeceleration task. Clinical Biomechanics, 14: 247-257.
343. Steiner, L.A., Harris, B.A. & Krebs, D.E. (1993). Reliability of eccentricisokinetic knee flexion and extension measurements. Archives of PhysicalMedicine and Rehabilitation, 74: 1327-1335.
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380. Voigt, M. & Klausen, K. (1990). Changes in muscle strength and speedon an unloaded movement after various training programmes. EuropeanJournal of Applied Physiology, 60: 370-376.
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383. Walshe, A.D., Wilson, G.J. & Ettema, G.J.C. (1997). Stretch-shortencycle compared with isometric preload: contibutions to enhanced muscularperformance. Journal of Applied Physiology, 84(1): 97-106.
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385. Wang, N., Hikida, R.S., Staron, R.S. & Simoneau, J. (1993). Musclefibre types of women after resistance training – quantitative ultrastructureand enzyme activity. European Journal Physiology, 424: 494-502.
386. Weijs, W.A. & van der Wielen-Drent, T.K. (1982). Sarcomere lengthand EMG activity in some jaw muscles of the rabbit. Acta Anatomica, 113:178-188.
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388. Weir, J.P., Housh, D.J., Housh, T.J. & Weir, L.L. (1995a). The effect ofunilateral eccentric weight training and detraining on joint angle specificity,cross-training, and the bilateral deficit. Journal of Orthopaedic and SportsPhysical Therapy, 22(5): 207-215.
389. Weir, J.P., Housh, D.J., Housh, T.J. & Weir, L.L. (1997). The effect ofunilateral concentric weight training and detraining on joint anglespecificity, cross-training, and the bilateral deficit. Journal of Orthopaedic &Sports Physical Therapy. 25(4): 264-270.
390. Weir, J.P., Housh, T.J. & Weir, L.L. (1994). Electromyographicevaluation of joint angle specificity and cross-training after isometrictraining. Journal of Applied Physiology. 77(1): 197-201.
391. Weir, J.P., Housh, T.J., Weir, L.L. & Johnson, G.O. (1995b). Effects ofunilateral isometric strength training on joint angle specificity and cross-training. European Journal of Applied Physiology, 70: 337-343.
392. Whalen, R.G. (1985). Myosin isoenzymes as molecular markers formuscle physiology. Journal of Experimental Biology, 115:43-53.
393. Wickiewicz, T.L., Roy, R.R., Powell, P.L. & Edgerton, V.R. (1983).Muscle architecture of the human lower limb. Clinical Orthopaedics, 179:275-283.
394. Wickiewicz, T.L., Toy, R.R., Powell, P.L, Perrine, J.J. & Edgerton, V.R.(1984). Muscle architecture and force-velocity relationships in humans.Journal of Applied Physiology, 57(2): 435-443.
395. Wiemann, K. & Tidow, G. (1995). Relative activity of hip and kneeextensors in sprinting – implications for training. New Studies in Athletics,10(1): 29-49.
396. Wilhite, M.R., Cohen, E.R. & Wilhite, S.C. (1992). Reliability ofconcentric and eccentric measurements of quadriceps performance usingthe KIN-COM dynamometer: The effect of testing order for three differentspeeds. Journal of Sports Physical Therapy, 15(4): 175-182.
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397. Willems, M.E.T. & Huijing, P.A. (1994). Heterogeneity of meansarcomere length in different fibres: effects of length range of active forceproduced in rat muscle. European Journal of Applied Physiology, 68: 489-496.
398. Williams, P., Watt, P., Bicik, V. & Goldspink, G. (1986). Effect of stretchcombined with electrical stimulation on the type of sarcomeres produced atthe ends of muscle fibers. Experimental Neurology, 93: 500-509.
399. Williams, P.E. (1990). Use of intermittent stretch in the prevention ofserial sarcomere loss in immobilised muscle. Annals of the RheumaticDiseases, 49: 316-317.
400. Willoughby, D.S. (1993). The effects of mesocycle-length weighttraining programs involving periodization and partially equated volumes onupper and lower body strength. Journal of Strength and ConditioningResearch, 7(1): 2-8.
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APPENDIX A
ETHICS APPLICATION
BIOMECHANICAL AND CROSS-SECTIONAL ANALYSIS OF
FOUR RESISTANCE TRAINING EXERCISES
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Southern Cross University
Human Experimentation Ethics Committee
Proposed Project Using Experimental Procedures on HumanSubjects
INITIAL APPLICATION for approval for year 1997
1. Name of Project: Biomechanical and Cross-sectional Analysis of FourResistance Training Exercises
2. Name: Anthony Blazevich
Position: PhD Candidate
School: Exercise Science and Sport Management
Telephone Extension: 3231
3. Supervisor: Dr. Greg Wilson
4. Technicians associated with experiment:Mr. Robert BaglinMr. Mark Fisher
5. Funding - Have you received or applied for external funding of thisexperiment?
NO
6. Proposed date of commencement: September 15 1997.
7. Duration and estimated finishing date: October 31 1997.
8. Intended number of participants: 30 active male subjects, who haveexperience in weight training, will be voluntarily recruited from the Universityand local community.
9. Age range of participants: 18 - 30 yrs
10. Aim or purpose of the experiment: The purpose of the study is two-fold.The first purpose is to compare subject’s performances in several resistancetraining exercises with their performance in vertical jump, broad jump andsprint running tests. Resistance training exercises will include a reverse hacksquat (i.e. the subject performs a movement similar to a squat on a hacksquatmachine but faces the machine such that the body is prone but inclined to45o), barbell squat lift, Smith Machine squat lift and incline seated leg press
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(hereafter referred to as leg press). The second purpose is to describe thekinetics, kinematics and electromyogram (EMG) patterns of the fourresistance training exercises. The movement pattern and EMG will then becompared to that of the running acceleration phase of sprint running and thevertical jump as described in the literature.
11. Methodology of the proposed study (including the source ofparticipants and how they were selected), procedures (e.g. blood samples),and methods to be adopted:
Thirty experienced male and female weight trainers who also perform trainingwhich includes running (eg soccer, hockey or rugby players, recreationalathletes, etc.) will be recruited from the University population and local area.The subjects will perform maximal lifts with a load equal to 80% of maximumon the reverse hack squat, barbell squat, Smith Machine squat and leg pressexercises as well as performing vertical jump, broad jump and 20 m sprinttests over three days. The vertical jump tests will include both squat jumpswith (counter-movement jump, CMJ) and without (squat jump, SJ) a counter-movement (i.e. a noticeable dip of the body before the vertical jump).Subjects will be asked to perform a training session three days prior to thefirst testing day to become familiar with the resistance training exercises.Training will involve two sets of ten repetitions of each of the resistanceexercises at a weight which could be lifted only ten times in each set.
On the first day of testing, subjects will perform each resistance trainingexercise at incremental weights until a weight cannot be lifted after a thoroughwarm-up including 5 minutes of cycling and several submaximum lifts. Thus,a measure of each subject’s maximum lift (1 RM - one repetition maximum)will be determined. On the second day of testing - two days after thedetermination of 1RM’s - subjects will perform two maximal SJ’s, CMJ’s and20 m sprints from a standing start. A third repetition will be performed if thesecond trial is greater than the first. On the third day, maximum lifts with eachof the four resistance exercises with 80% of each subject’s 1 RM will beperformed. Force will be recorded on a force platform which will be positionedeither under the feet (for the squat lifts) or on face of the weighted sledge (forthe leg press). The force platform will register zero force when the subject isstanding on the platform with the weight taken on the shoulders (or, for the legpress, while the subject is supporting the weight). Two trials will be allowed,but a third trial will be allowed if the second lift is greater than the first.
To minimise fatigue, four minutes of passive rest will be allowed betweeneach 1 RM and 80% of 1 RM trial and between the 30 m sprints, while twominutes rest will be allowed between successive jumps. Ten minutes of restwill be allowed between each testing block (i.e. between 1 RM tests on eachresistance exercise, and between the jumps and sprints). Subjects will beallowed to perform low intensity cycle exercise or jogging to aid recoveryduring this period. The order of testing will be randomised for each subject oneach day. This should ensure that effects of fatigue or familiarisation do notresult in a bias towards any one test.
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During the testing period, ten male subjects will be randomly selected toparticipate in a biomechanical analysis of the resistance training movements.EMG data will be recorded from eight muscles (as described below) by bipolarsurface electrodes prior to a video analysis of the same movement.
(If there is insufficient space, an addendum should be attached)
12. Indicate any potential risk you can envisage to the participants andsafety precautions to be taken.
Subjects will be required to exert maximum effort during the testing sessionsand as such there is always the possibility that muscular strains can occur.However, only previously trained subjects are to be recruited as subjects andall subjects will be thoroughly warmed up prior to testing. Further, the testingwill be strictly supervised such that appropriate loads and techniques areemployed on all exercises. Dermal infection has also been reported afterplacement of EMG electrodes on the skin. To prevent infection, alcohol willbe applied to the skin prior to electrode placement and an antiseptic creamwill be applied to the skin after the electrodes have been removed.
13. Comment of any relevant ethical considerations, and attach theconsent form to be signed by participants, for approval.
The project is a standard cross-sectional and biomechanical study involvingtesting methods which are common practice and have been successfully andsafely performed by the investigator on a number of occasions.
A copy of the consent form to be signed by participants must be attached forapproval.
14. Comments (if thought necessary from Head of School e.g. onrelationship of this experiment to current practice in the discipline.
Signed Head of School: ________________________________
Date: ____________________
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15. Certification:
I, the person responsible, certify that the proposed experiment will confirmwith the general principles set out in the N.H. and M.R.C. “Statement onHuman Experimentation and Supplementary Notes (1987)”.
Signed: _____________________________ Date: _____________
Supervisor: __________________________ Date: _____________
Approval of Committee on Ethics in Experimentation of Human Participants:
Signed: _____________________________ Date: ______________
Approval No: ________________________ Issued: ____________
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Southern Cross University
FORM OF DISCLOSURE AND INFORMED CONSENT
Biomechanical and Cross-sectional Analysis of Four Resistance TrainingExercises
You are invited to participate in a study designed to compare subject’sperformances in four resistance training exercises (reverse hack squat,barbell squat, Smith Machine squat and leg press) with their performance invertical jump, broad jump and sprint running tests, and to describe the kinetics(forces), kinematics (motions) and electromyogram (EMG) patterns of the fourresistance training exercises. The movement pattern and EMG will then becompared to that of the running acceleration phase of sprint running and thevertical jump as described in the literature.
PROCEDURES TO BE FOLLOWEDAll testing will be carried out in the Biomechanics and Rehabilitation ResearchLaboratories of the School of Exercise Science and Sport Management. Afterperforming a training session three days prior to the first testing day tobecome familiar with the resistance training exercises, subjects will undergothree days of testing. On the first day of testing, subjects will perform eachresistance training exercise (the reverse hack squat, barbell squat, SmithMachine squat and leg press) at incremental weights until a weight cannot belifted. Thus, a measure of each subject’s maximum lift (1 RM - one repetitionmaximum) will be determined. On the second day of testing, two days afterthe determination of 1RM’s, subjects will perform two maximal SJ’s, CMJ’sand 20 m sprints from a standing start. A third repetition will be performed ifthe second trial is greater than the first. On the third day, maximum lifts witheach of the four resistance with 80% of their 1RM will be performed. Forcewill be recorded on a force platform which will be positioned either under thefeet (for the squat lifts) or on face of the weighted sledge (for the leg press).The force platform will register zero force when the subject is standing on theplatform with the weight taken on the shoulders (or, for the leg press, whilethe subject is supporting the weight). Two trials will be allowed, but a thirdtrial will be allowed if the second lift is greater than the first..
During the testing period, ten male subjects will be randomly selected toparticipate in a biomechanical analysis of the resistance training movements.EMG data will be recorded from eight muscles (as described below) by bipolarsurface electrodes prior to a video analysis of the same movement.Participation in the biomechanical analysis is not dependent uponparticipation in the cross-sectional analysis.
The above are standard tests of lower body strength and power. Further, thebiomechanical analysis is similar to that performed in numerous previousstudies. To minimise fatigue during the three days of testing, four minutes ofpassive rest will be allowed between each 1 RM and 80% of 1 RM trial and
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between the 30 m sprints, while two minutes rest will be allowed betweensuccessive jumps. Ten minutes of rest will be allowed between each testingblock (i.e. between 1 RM tests on each resistance exercise, and between thejumps and sprints). Subjects will be allowed to perform low intensity cycleexercise or jogging to aid recovery during this period. The order of testing willbe randomised for each subject on each day. This should ensure that effectsof fatigue or familiarisation do not result in a bias towards any one test.
POSSIBLE SUBJECT DISCOMFORTS/RISKS
Subjects may experience some muscular soreness after the familiarisationand testing sessions. Further, the performance of maximal muscularcontractions, either during the testing or familiarisation sessions, has apotential to result in muscular strains. All necessary safe guards (includingproper warm-up and supervision) will be used to minimise such anoccurrence. Also, acute dermal infections have been reported after EMGelectrode use. To eliminate the chance of infection, an alcohol solution will beapplied to the skin prior to EMG electrode placement and an antiseptic creamwill be applied after EMG electrode removal.
SUBJECT BENEFITS
Subjects can benefit from participation in the study by:Having the opportunity to observe methods of experimental research in thisarea.Contributing to the advancement of science as a research participant.Obtaining information and advice on strength and power training.Being first to obtain the results and practical implications of the study.Having their lower body strength and power, and sprinting and jumpingabilities tested at no expense.
INVESTIGATOR RESPONSIBILITIES
Any information that is obtained in connection with this study and thatcan be identified with you will remain confidential and will be disclosed onlywith your permission.
If you decide to participate, you are free to withdraw your consent andto discontinue participation at any time without prejudice. However, priornotice of withdrawal would be appreciated.
If you have any questions, please contact Tony Blazevich on (H) 223 763 or(Uni) 203 231, at any time.
You will be given a copy of this form to keep.
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SUBJECT’S DECLARATION OF CONSENT
I _________________________________ , being over eighteen years of ageconsent to being a subject in the research project “Biomechanical and Cross-sectional Analysis of Four Resistance Training Exercises”.
I have been given a copy of a “Form of Disclosure and Informed Consent”document which I fully understand describing the procedures to be followedand the consequences and risks involved in my participation as a subject.
I have read the information above and any questions I have asked have beenanswered to my satisfaction. I agree to participate in this activity, realisingthat I may withdraw without prejudice at any time.
I agree that research data gathered from the study may be published providedmy name is not used.
NAME OF SUBJECT ______________________________
SIGNATURE OF SUBJECT _________________________DATE ____________
NAME OF WITNESS ______________________________
SIGNATURE OF WITNESS _________________________DATE ____________
SIGNATURE OF RESEARCHER _____________________DATE ____________
certifying that the terms of the form have been verbally explained to thesubject, that the subject appears to understand the terms prior to signing theform, and that proper arrangements have been made for an interpreter whereEnglish is not the subjects first language.
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APPENDIX B
ETHICS APPLICATION
INFLUENCE OF MOVEMENT PATTERN OF RESISTANCE
TRAINING EXERCISES ON VERTICAL JUMP AND SPRINT
RUNNING PERFORMANCE DURING CONCURRENT
RESISTANCE AND TASK TRAINING
258
Southern Cross University
Human Experimentation Ethics Committee
Proposed Project Using Experimental Procedures on HumanSubjects
INITIAL APPLICATION for approval for year 1999
1. Name of Project: Influence of movement pattern of resistance trainingexercises on vertical jump and sprint running performance during concurrentresistance and task training
2. Name: Anthony Blazevich
Position: PhD Candidate
School: Exercise Science and Sport Management
Telephone Extension: 3231
3. Supervisor: Dr. Robert Newton
4. Technicians associated with experiment:Mr. Robert BaglinMr. Mark Fischer
5. Funding - Have you received or applied for external funding of thisexperiment?Submitted full version to American Society of Biomechanics Graduate StudentGrant-in-aid scheme.
6. Proposed date of commencement: March 21, 1999.
7. Duration and estimated finishing date: June 1, 1999.
8. Intended number of participants: 60 active male subjects will bevoluntarily recruited from the University and local community.
9. Age range of participants: 18 - 30 yrs
Aim or purpose of the experiment: The present investigation will examine theperformance changes of complex tasks (vertical jump and acceleration phaseof a sprint run) while task training is performed with resistance training (eitherthe squat lift or a new forward hack squat exercise). In addition, performancechanges after concurrent task and resistance training will be compared toperformance changes of subjects performing no resistance training but twice
259
the number of task training sessions.
11. Methodology of the proposed study (including the source ofparticipants and how they were selected), procedures (e.g. blood samples),and methods to be adopted:
Experimental Design:Training will consist of a four-week familiarisation training phase in which allsubjects will perform sprint running (20 m) and vertical jump training twice aweek in addition to two resistance training sessions a week. The resistancetraining will consist of exercises that can be regarded as being non-specific tothe vertical jump and sprint running tasks. The familiarisation period willincorporate that period of training where substantial performanceimprovements in vertical jump and sprint running would occur. Thus, smallerimprovements are likely during the specific phase of training. The specificphase of training will last 6 weeks, short enough for minimal increases inhypertrophy to occur and for architectural (including sarcomere lengthchanges) and neural adaptations to be the most likely culprits for adaptation.During this phase of training, subjects will be organised into three traininggroups (2 experimental and 1 control), one group will dominantly use thesquat lift (or jump squat) and one group the one-legged forward hack squatduring their resistance training. Biomechanical analyses in our laboratoryhave compared and contrasted several versions of the vertical jump andsquat lift as well as examining the forward hack squat. Versions of theseexercises have been found that are very similar and could be deemedmovement pattern-specific. Other supplementary exercises will also beperformed during the training. Both of experimental groups will also performtwo vertical jump and sprint running sessions a week. The third, control,group will perform no resistance training but will participate in four verticaljump and sprint running sessions a week. Subjects will undergo a series oftests before and after this six-week specific training period.
Resistance TrainingDuring the ‘non-specific’ training phase, all subjects, including the controls,will perform resistance training twice a week with the dominant exercise beingthe leg press (incline). Other supplementary exercises will include the legextension, leg flexion (leg curl), deadlift and standing calf raise exercises.Four sets of leg press will be performed and two sets of all other exercises.Weights will be increased such that in week one, subjects will perform sets of12 repetitions and proceed to sets of 6 – 8 by the fourth week. Thus, allsubjects will perform general strengthening prior to the specific training phase.
During the ‘specific’ training phase, the two experimental groups will use their‘specific’ exercise as the dominant movement. Training will alternate suchthat the first session of each week is performed at weights of 80% of 1 RMwhile in the second session weights of 30% of 1 RM will be used. The ‘squat’group will perform the bilateral squat lift as their dominant exercise with all liftsbeing performed with a maximal concentric phase. As such, the exercisecould be likened to the jump squat since most subjects will leave the ground
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at the end of the concentric phase. The eccentric phase will always beperformed over a 1 – 2 s period. In the first week, the subjects will perform 3sets of 6 repetitions of the squat exercise after 2 warm-up sets at increasingweights. Training will progress to 4 sets of 8 repetitions by the end of thetraining period. Supplementary training will include 3 sets of 10 repetitions ofprone back extension, 3 sets of 10 repetitions of leg curl and 3 sets of 10repetitions of the standing calf raise exercise. The group using the forwardhack squat exercise (‘FHS’) will perform the task unilaterally in training. Thus,while each leg might perform those repetitions in which they are directlyinvolved, synergist and fixator musculature will be involved in all repetitions.As such, training will be adjusted accordingly. In the first week, the subjectswill perform 2 sets of 6 repetitions on each leg after 2 warm-up sets atincreasing weights. Training will progress to 3 sets of 8 repetitions by the endof the training period. As for the squat group, all movements will beperformed with a maximal concentric phase with the weight being stopped atthe top of its movement by a spring to prevent injury. Supplementary trainingwill be identical to the squat group. Weights used by both groups will beincreased over the training period as their performances in these lifts improve.
Vertical Jump and Sprint Running Training
Experimental subjects will perform two sessions, while the control group willperform four session, each week. After a thorough warm-up, subjects willperform sets of 20 m sprint and vertical jumps. In the first session each week,sprint training will be performed first while in the second session verticaljumps will be performed first. This should eliminate the effects of fatigue onlearning and performance. In the first week, subjects will perform sessionsinvolving 3 x 30 m sprints and 3 sets of 3 countermovement jumps with oneminute rest between sets. By the end of the full 10 weeks of training, trainingwill increase to 6 x 30 m sprints and 6 sets of 4 countermovement jumps with4 minutes rest between sprints and 2 minutes rest between sets of jumps. Allsubjects will be briefed on the fundamentals of sprint running and verticaljumping during the familiarisation period.
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Testing
Testing will be performed immediately prior and subsequent to the six weekspecific training phase with the test battery for each subject being spacedover several sessions to minimise fatigue.
1) Squat lift: squat lifts with a maximal concentric phase and an eccentricphase lasting 1 – 2 s will be performed on a force platform. Performancemeasures will include maximum force, time at which maximum force occurredand impulse during the concentric phase of the movement. In addition, bardisplacement will be registered by use of a flywheel instrument attached to thebar from which the concentric and eccentric phases can be discerned and barvelocity can be calculated. Subjects first perform a maximal isometric squatat the bottom position of a squat (individually determined at the point theirlowest point in a jump squat) and maximum force will be measured. Squat lifttesting will then be performed with weights equivAlént to 30% and 80% of thismaximum isometric force. By not performing lifts with maximum weight, therisk of injury should be dramatically reduced. Since the aim of the presentstudy is to investigate the effect of movement pattern, rather than velocity, oftraining exercises, testing after the 6 week training period will utilise thesesame weights, rather than a new weight that is congruent with subject’sstrength increases. Thus, subjects’ performances will be compared at a givenweight, similar to the vertical jump where weights are not changed aftertraining. Subjects will be allowed three attempts at each.2) Forward Hack Squat: after measuring subjects isometric force at thebottom of the forward hack squat movement, subjects will perform maximalone- and two-legged forward hack squats with a 1 – 2 s eccentric phase.Measures will be as per the squat lift. Subjects will be allowed three attemptsat each.3) Countermovement Vertical Jump: subjects will jump for maximumheight on a force platform. Ground reaction forces will be mearsured for eachjump from which body displacement will be estimated. Thus, problemsassociated with jump and reach tests will be eliminated. Subjects will performboth one- and two-legged trials; three repetitions will be performed of each.4) Sprint Test: 10 m and 20 m sprint times will be recorded during a 20 mmaximal sprint. Subjects will begin from a standing start with one foot in frontof the other but will be allowed to bend the knees to lower the body’s centre ofgravity. Subjects will be allowed three trials.5) Muscle Pennation and Thickness Tests: ultrasound will be used toimage the vastus lateralis and rectus femoris of subjects (10 subjects fromeach group only). For the rectus femoris, photographs will be taken at points20% and 50% of the distance from the tendomuscular junction (clearly visiblein most subjects) to its attachment at the hip. Thus measures of pennation,thickness and anatomical cross-sectional area will be taken at the midpointand at one end of the muscle. For vastus lateralis, photographs will be takenat 20% and 50% of the distance from the lateral condyle of the femur to thegreater trochanter.6) Electromyographic Analysis of the Vertical Jump and Sprint Run: Afterstandard skin preparation including hair removal, light abrasion with
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sandpaper and swabbing with disinfecting alcohol, 8 subjects from each ofthe three groups will perform two-legged vertical jumps and 10 m sprints withelectrodes placed on their gluteus maximus, vastus lateralis, biceps femoris(long head), illiopsoas and rectus femoris muscles. Timing of musclecontractions and level of cocontraction will subsequently be estimated. Allsubjects will be filmed to ascertain key events during each task; an LED willbe used to synchronise EMG and video data.7) Isokinetic Knee Extension: To examine changes in the torque-anglerelationship about the knee, subjects will perform slow (30o.s-1) and fast(300o.s-1) isokinetic knee extensions. An isometric pre-load force will beimposed prior to the movement to minimise force spikes at the onset ofmovement and provide more reliable force measures in the early part of themovement. Biomechanical analyses suggest that the angle through which theknee moves differs between the squat and FHS exercises making this jointideal for torque-angle testing.
Statistical Analysis
After testing for normality of the data, repeated measures ANOVA’s with twofactors (group and time) will examine differences in performance from pre- topost-training. An Alpha Level of 0.05 will be used to minimise type I error.Correlation coefficients will also be calculated to examine relationshipsbetween test performances, and between changes in test performances andchanges in physiological variables (eg muscle thickness, pennation, level ofco-contraction, joint-specific torque, etc.).
12. Indicate any potential risk you can envisage to the participants andsafety precautions to be taken.
Subjects will be required to exert maximum effort during the testing sessionsand as such there is always the possibility that muscular strains can occur.However, only previously trained subjects are to be recruited as subjects andall subjects will be thoroughly warmed up prior to testing. Further, the testingwill be strictly supervised such that appropriate loads and techniques areemployed on all exercises. Dermal infection has also been reported afterplacement of EMG electrodes on the skin. To prevent infection, alcohol willbe applied to the skin prior to electrode placement and an antiseptic creamwill be applied to the skin after the electrodes have been removed.
13. Comment of any relevant ethical considerations, and attach theconsent form to be signed by participants, for approval.
The project is a standard training study involving testing methods which arecommon practice and have been successfully and safely performed by theinvestigator on a number of occasions.
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14. Comments (if thought necessary from Head of School e.g. onrelationship of this experiment to current practice in the discipline.
Signed Head of School: ________________________________
Date: ____________________
15. Certification:
I, the person responsible, certify that the proposed experiment will confirmwith the general principles set out in the N.H. and M.R.C. “Statement onHuman Experimentation and Supplementary Notes (1987)”.
Signed: _____________________________ Date: ___________________
Supervisor: __________________________ Date: ___________________
Approval of Committee on Ethics in Experimentation of Human Participants:
Signed: _____________________________ Date: ___________________
Approval No: ________________________ Issued: __________________
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Southern Cross University
FORM OF DISCLOSURE AND INFORMED CONSENT
Influence of movement pattern of resistance training exercises on verticaljump and sprint running performance during concurrent resistance and tasktraining
You are invited to participate in a study designed to examine the performancechanges of complex tasks (vertical jump and acceleration phase of a sprintrun) while task training is performed with resistance training (either the squatlift or a new forward hack squat exercise). In addition, performance changesafter concurrent task and resistance training will be compared to performancechanges of subjects performing no resistance training but twice the number oftask training sessions.
PROCEDURES TO BE FOLLOWED
Experimental Design:Training will consist of a four-week familiarisation training phase in which allsubjects will perform sprint running (20 m) and vertical jump training twice aweek in addition to two resistance training sessions a week. The resistancetraining will consist of exercises that can be regarded as being non-specific tothe vertical jump and sprint running tasks. The familiarisation period willincorporate that period of training where substantial performanceimprovements in vertical jump and sprint running would occur. Thus, smallerimprovements are likely during the specific phase of training. The specificphase of training will last 6 weeks, short enough for minimal increases inhypertrophy to occur and for architectural (including sarcomere lengthchanges) and neural adaptations to be the most likely culprits for adaptation.During this phase of training, subjects will be organised into three traininggroups (2 experimental and 1 control), one group will dominantly use thesquat lift (or jump squat) and one group the one-legged forward hack squatduring their resistance training. Biomechanical analyses in our laboratoryhave compared and contrasted several versions of the vertical jump andsquat lift as well as examining the forward hack squat. Versions of theseexercises have been found that are very similar and could be deemedmovement pattern-specific. Other supplementary exercises will also beperformed during the training. Both of experimental groups will also performtwo vertical jump and sprint running sessions a week. The third, control,group will perform no resistance training but will participate in four verticaljump and sprint running sessions a week. Subjects will undergo a series oftests before and after this six-week specific training period.
Resistance TrainingDuring the ‘non-specific’ training phase, all subjects, including the controls,will perform resistance training twice a week with the dominant exercise being
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the leg press (incline). Other supplementary exercises will include the legextension, leg flexion (leg curl), deadlift and standing calf raise exercises.Four sets of leg press will be performed and two sets of all other exercises.Weights will be increased such that in week one, subjects will perform sets of12 repetitions and proceed to sets of 6 – 8 by the fourth week. Thus, allsubjects will perform general strengthening prior to the specific training phase.
During the ‘specific’ training phase, the two experimental groups will use their‘specific’ exercise as the dominant movement. Training will alternate suchthat the first session of each week is performed at weights of 80% of 1 RMwhile in the second session weights of 30% of 1 RM will be used. The ‘squat’group will perform the bilateral squat lift as their dominant exercise with all liftsbeing performed with a maximal concentric phase. As such, the exercisecould be likened to the jump squat since most subjects will leave the groundat the end of the concentric phase. The eccentric phase will always beperformed over a 1 – 2 s period. In the first week, the subjects will perform 3sets of 6 repetitions of the squat exercise after 2 warm-up sets at increasingweights. Training will progress to 4 sets of 8 repetitions by the end of thetraining period. Supplementary training will include 3 sets of 10 repetitions ofprone back extension, 3 sets of 10 repetitions of leg curl and 3 sets of 10repetitions of the standing calf raise exercise. The group using the forwardhack squat exercise (‘FHS’) will perform the task unilaterally in training. Thus,while each leg might perform those repetitions in which they are directlyinvolved, synergist and fixator musculature will be involved in all repetitions.As such, training will be adjusted accordingly. In the first week, the subjectswill perform 2 sets of 6 repetitions on each leg after 2 warm-up sets atincreasing weights. Training will progress to 3 sets of 8 repetitions by the endof the training period. As for the squat group, all movements will beperformed with a maximal concentric phase with the weight being stopped atthe top of its movement by a spring to prevent injury. Supplementary trainingwill be identical to the squat group. Weights used by both groups will beincreased over the training period as their performances in these lifts improve.
Vertical Jump and Sprint Running Training
Experimental subjects will perform two sessions, while the control group willperform four session, each week. After a thorough warm-up, subjects willperform sets of 20 m sprint and vertical jumps. In the first session each week,sprint training will be performed first while in the second session verticaljumps will be performed first. This should eliminate the effects of fatigue onlearning and performance. In the first week, subjects will perform sessionsinvolving 3 x 30 m sprints and 3 sets of 3 countermovement jumps with oneminute rest between sets. By the end of the full 10 weeks of training, trainingwill increase to 6 x 30 m sprints and 6 sets of 4 countermovement jumps with4 minutes rest between sprints and 2 minutes rest between sets of jumps. Allsubjects will be briefed on the fundamentals of sprint running and verticaljumping during the familiarisation period.
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Testing
Testing will be performed immediately prior and subsequent to the six weekspecific training phase with the test battery for each subject being spacedover several sessions to minimise fatigue.
1) Squat lift: squat lifts with a maximal concentric phase and an eccentricphase lasting 1 – 2 s will be performed on a force platform. Performancemeasures will include maximum force, time at which maximum force occurredand impulse during the concentric phase of the movement. In addition, bardisplacement will be registered by use of a flywheel instrument attached to thebar from which the concentric and eccentric phases can be discerned and barvelocity can be calculated. Subjects first perform a maximal isometric squatat the bottom position of a squat (individually determined at the point theirlowest point in a jump squat) and maximum force will be measured. Squat lifttesting will then be performed with weights equivalent to 30% and 80% of thismaximum isometric force. Since the aim of the present study is to investigatethe effect of movement pattern, rather than velocity, of training exercises,testing after the 6 week training period will utilise these same weights, ratherthan a new weight that is congruent with subject’s strength increases. Thus,subjects’ performances will be compared at a given weight, similar to thevertical jump where weights are not changed after training. Subjects will beallowed three attempts at each.2) Forward Hack Squat: after measuring subjects isometric force at thebottom of the forward hack squat movement, subjects will perform maximalone- and two-legged forward hack squats with a 1 – 2 s eccentric phase.Measures will be as per the squat lift. Subjects will be allowed three attemptsat each.3) Countermovement Vertical Jump: subjects will jump for maximumheight on a force platform. Ground reaction forces will be measured for eachjump from which body displacement will be estimated. Thus, problemsassociated with jump and reach tests will be eliminated. Subjects will performboth one- and two-legged trials; three repetitions will be performed of each.4) Sprint Test: 10 m and 20 m sprint times will be recorded during a 20 mmaximal sprint. Subjects will begin from a standing start with one foot in frontof the other but will be allowed to bend the knees to lower the body’s centre ofgravity. Subjects will be allowed three trials.5) Muscle Pennation and Thickness Tests: ultrasound will be used toimage the vastus lateralis and rectus femoris of subjects (10 subjects fromeach group only). For the rectus femoris, photographs will be taken at points20% and 50% of the distance from the tendomuscular junction (clearly visiblein most subjects) to its attachment at the hip. Thus measures of pennation,thickness and anatomical cross-sectional area will be taken at the midpointand at one end of the muscle. For vastus lateralis, photographs will be takenat 20% and 50% of the distance from the lateral condyle of the femur to thegreater trochanter.6) Electromyographic Analysis of the Vertical Jump and Sprint Run: 8subjects from each of the three groups will perform two-legged vertical jumpsand 10 m sprints while electrodes are placed on the gluteus maximus, vastus
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lateralis, biceps femoris (long head), illiopsoas and rectus femoris muscles.Timing of muscle contractions and level of cocontraction will subsequently beestimated. All subjects will be filmed to ascertain key events during eachtask; an LED will be used to synchronise EMG and video data.7) Isokinetic Knee Extension: To examine changes in the torque-anglerelationship about the knee, subjects will perform slow (30o.s-1) and fast(300o.s-1) isokinetic knee extensions. An isometric pre-load force will beimposed prior to the movement to minimise force spikes at the onset ofmovement and provide more reliable force measures in the early part of themovement. Biomechanical analyses suggest that the angle through which theknee moves differs between the squat and FHS exercises making this jointideal for torque-angle testing.
POSSIBLE SUBJECT DISCOMFORTS/RISKS
Subjects may experience some muscular soreness after the familiarisationand testing sessions. Further, the performance of maximal muscularcontractions, either during the testing or training sessions, has a potential toresult in muscular strains. All necessary safe guards (including proper warm-up and supervision) will be used to minimise such an occurrence. Also, acutedermal infections have been reported after EMG electrode use. To eliminatethe chance of infection, an alcohol solution will be applied to the skin prior toEMG electrode placement and an antiseptic cream will be applied after EMGelectrode removal.
SUBJECT BENEFITS
Subjects can benefit from participation in the study by:Opportunity to improve speed and strength by taking part in a supervised,periodised training regime.Being tested on two occasions to determine level of training and rate ofimprovement.Free use of an air conditioned gym for training.Obtaining information and advice on strength and power training.Having the opportunity to observe methods of experimental research in thisarea.Contributing to the advancement of science as a research participant.Being first to obtain the results and practical implications of the study.
INVESTIGATOR RESPONSIBILITIES
Any information that is obtained in connection with this study and thatcan be identified with you will remain confidential and will be disclosed onlywith your permission.
If you decide to participate, you are free to withdraw your consent andto discontinue participation at any time without prejudice. However, priornotice of withdrawal would be appreciated.
If you have any questions, please contact Tony Blazevich on (H) 216 617 or
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(Uni) 203 231, at any time.
You will be given a copy of this form to keep.
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SUBJECT’S DECLARATION OF CONSENT
I _________________________________ , being over eighteen years of ageconsent to being a subject in the research project “Influence of movementpattern of resistance training exercises on vertical jump and sprint runningperformance during concurrent resistance and task training”.
I have been given a copy of a “Form of Disclosure and Informed Consent”document which I fully understand describing the procedures to be followedand the consequences and risks involved in my participation as a subject.
I have read the information above and any questions I have asked have beenanswered to my satisfaction. I agree to participate in this activity, realisingthat I may withdraw without prejudice at any time.
I agree that research data gathered from the study may be published providedmy name is not used.
NAME OF SUBJECT ______________________________
SIGNATURE OF SUBJECT _________________________DATE ____________
NAME OF WITNESS ______________________________
SIGNATURE OF WITNESS _________________________DATE ____________
SIGNATURE OF RESEARCHER _____________________DATE ____________
certifying that the terms of the form have been verbally explained to thesubject, that the subject appears to understand the terms prior to signing theform, and that proper arrangements have been made for an interpreter whereEnglish is not the subjects first language.
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APPENDIX C
STATEMENT OF INFORMED CONSENT
RELIABILITY AND VALIDITY OF ISOMETRIC SQUAT AND
FORWARD HACK SQUAT TESTS
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Southern Cross University
FORM OF DISCLOSURE AND INFORMED CONSENT
Reliability and validity of isometric squat and forward hack squattests.
You are invited to participate in a study designed to examine the reliability andvalidity of isometric squat and forward hack squat tests.
PROCEDURES TO BE FOLLOWED
Experimental Design:
Subjects will attend two 45-min testing sessions. Each session will involve 3isometric squat lifts, 3 isometric forward hack squat (FHS) lifts, and theperformance of 1 repetition maximum (1 RM) of either the squat or FHS.
Testing
Squat: Subjects will stand under an immoveable bar with a knee angleof 90o and the bar resting across the shoulders. When instructed, subjectswill push upward against the bar with maximal exertion. Force producedduring the push will be recorded by force platform.
FHS: Subjects will position themselves on the FHS machine with aknee angle of 90o and a hip angle of 110o. When instructed, the subjects willpush upward against shoulder pads that are immoveable. Force producedduring the push will be recorded by load cell.
1 RM squat: After warm up including several repetitions of submaximal squatlifts, subjects will perform single squat lifts with the weight being increasedincrementally until the weight cannot be lifted. Metal stops will prevent the barand weights from moving below a predetermined level to minimise injury risk.The maximum weight lifted will be taken as that subject’s 1 RM.
1 RM FHS: After warm up including several repetitions of submaximal FHSlifts, subjects will perform single FHS lifts with the weight being increasedincrementally until the weight cannot be lifted. Metal stops will prevent thesled and weights from moving below a predetermined level to minimise injuryrisk. The maximum weight lifted will be taken as that subject’s 1 RM.
Following the testing, reliability of the isometric lifts will be calculated, and therelationship between isometric and 1 RM strength will be determined.
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POSSIBLE SUBJECT DISCOMFORTS/RISKS
Subjects may experience some muscular soreness after the testing sessions.Further, the performance of maximal muscular contractions can potentiallyresult in muscular strains. All necessary safe guards (including proper warm-up and supervision) will be used to minimise such an occurrence.
SUBJECT BENEFITS
Subjects can benefit from participation in the study by:Obtaining information and advice on strength and power training.Having the opportunity to observe methods of experimental research in thisarea.Contributing to the advancement of science as a research participant.
INVESTIGATOR RESPONSIBILITIES
Any information that is obtained in connection with this study and thatcan be identified with you will remain confidential and will be disclosed onlywith your permission.
If you decide to participate, you are free to withdraw your consent andto discontinue participation at any time without prejudice. However, priornotice of withdrawal would be appreciated.
If you have any questions, please contact Tony Blazevich on (Uni) 66 203231, at any time.
You will be given a copy of this form to keep.
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SUBJECT’S DECLARATION OF CONSENT
I _________________________________ , being over eighteen years of ageconsent to being a subject in the research project “Reliability and validity ofisometric squat and forward hack squat tests.”.
I have been given a copy of a “Form of Disclosure and Informed Consent”document that I fully understand describing the procedures to be followed andthe consequences and risks involved in my participation as a subject.
I have read the information above and any questions I have asked have beenanswered to my satisfaction. I agree to participate in this activity, realisingthat I may withdraw without prejudice at any time.
I agree that research data gathered from the study may be published providedmy name is not used.
NAME OF SUBJECT ______________________________
SIGNATURE OF SUBJECT _________________________DATE ____________
NAME OF WITNESS ______________________________
SIGNATURE OF WITNESS _________________________DATE ____________
SIGNATURE OF RESEARCHER _____________________DATE ____________
certifying that the terms of the form have been verbally explained to thesubject, that the subject appears to understand the terms prior to signing theform, and that proper arrangements have been made for an interpreter whereEnglish is not the subjects first language.
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APPENDIX D
TRAINING PROGRAMS
EXAMPLE RESISTANCE TRAINING PROGRAMS FOR SQ
(SQUAT) AND FHS (FORWARD HACK SQUAT) GROUPS
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Gym Training ProgramName: Person ATraining Group: SquatPredicted Maximum: 189.12 kg
Weights for Heavy Sessions should range from approximately:Week 1 85.96 – 107.46 kgWeek 5 128.95 – 150.44 kg
Weights for Explosive Sessions should range from approximately:Week 1 42.98 – 64.47 kgWeek 5 64.47 – 85.96 kg
Heavy day program:
Warm-up on squats bar only, 8 repsWarm-up on squats, 20% of max. predicted = 40 kg, 8 repsSet 1, 30 - 40% of max. predicted = 60 - 85 kg, 8 repsSet 2, use weight in range above (heavy) = 6 repsSet 3, use weight in range above = 6 repsSet 4, use weight in range above = 6 reps
2 sets of 10 repetitions of back extension (use weights if required)3 sets of 8 repetitions of leg curl (heavy and controlled)2 - 3 sets of 8 calf raises (heavy and controlled)
Light day program:
Warm-up on squats bar only, 8 repsWarm-up on squats, 20% of max. predicted = 40 kg, 8 repsSet 1, 30 - 40% of max. predicted = 60 - 85 kg, 8 repsSet 2, use weight in range above (light) = 6 repsSet 3, use weight in range above = 6 repsSet 4, use weight in range above = 6 reps
2 sets of 10 repetitions of back extension (use weights if required)3 sets of 8 repetitions of leg curl (slightly lighter and faster)2 - 3 sets of 8 calf raises (slightly lighter and faster, slow down, fastup)
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Gym Training ProgramName: Person BTraining Group: Forward Hack SquatPredicted Maximum: 103.65 kg
Weights for Heavy Sessions should range from approximately:Week 1 14.53 – 32.35 kgWeek 5 50.18 – 68.00 kg
Weights for Explosive Sessions should range from approximately:Week 1 0 kgWeek 5 0 – 14.5 kg
Heavy day program:
Warm-up on squats bar only, 8 repsWarm-up on squats, 20% of max. predicted = 0kg, 8 repsSet 1, 30 - 40% of max. predicted = 0 kg, 8 repsSet 2, use weight in range above (heavy) = 6 repsSet 3, use weight in range above = 6 reps
2 sets of 10 repetitions of back extension (use weights if required)3 sets of 8 repetitions of leg curl (heavy and controlled)2 - 3 sets of 8 calf raises (heavy and controlled)
Light day program:
Warm-up on squats bar only, 8 repsWarm-up on squats, 20% of max. predicted = 0 kg, 8 repsSet 1, 30 - 40% of max. predicted = 0 kg, 8 repsSet 2, use weight in range above (light) = 6 repsSet 3, use weight in range above = 6 reps
2 sets of 10 repetitions of back extension (use weights if required)3 sets of 8 repetitions of leg curl (slightly lighter and faster)2 - 3 sets of 8 calf raises (slightly lighter and faster, slow down, fastup)
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APPENDIX F
RELIABILITY STUDY
A COMPARISON OF DIGITAL CURVIMETER AND
MATHEMATICAL ESTIMATES OF FASCICLE LENGTH IN
CONTRACTING MUSCLE.
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ABSTRACT
Fascicle length can be measured in vivo by ultrasound techniques, although
two methods of estimating fascicle length are currently used: mathematical
estimation and curvimeter measurement. The purpose of this study was to
first to determine if significant differences exist between fascicle length
measures estimated by mathematical and curvimeter methods, and second to
examine the reliability of the mathematical procedure relative to the
curvimeter procedure. Photographs of up to nine sites on the gastrocnemius
medialis muscle of six subjects were taken using ultrasound imaging.
Photographs were taken in both relaxed and contracted (plantarflexion at 50%
of maximum) conditions and muscle thickness, pennation and fascicle length
subsequently measured. Differences between mathematical and curvimeter
estimates of fascicle length were examined by multilevel regression analysis.
There was no significant difference between fascicle length measures
estimated by the two methods, although differences were greater for the
relaxed and relaxed-contracted (change in fascicle length from relaxed to
contracted state) conditions compared to the contracted condition. Reliability
of single estimates were high for the curvimeter method (Intraclass
correlations [ICC’s] = 0.75 – 0.91) but low for mathematical estimation (ICC’s
= 0.39 – 0.60). Nonetheless, by averaging a number (N=9) of repeated
measurements on the subjects, reliability of the mathematical method was
increased significantly (ICC’s = 0.85 – 0.93). These results suggest that, for
the gastrocnemius medialis muscle, there was little difference between
fascicle length estimated by mathematical or curvimeter methods although the
reliability of mathematical estimates was very low, and statistical power would
be dramatically reduced. Nonetheless, reliability of a number of repeated
measurements was high and comparable to the curvimeter method.
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INTRODUCTION
Muscle contraction properties are strongly influenced by architectural
characteristics such as muscle size, pennation (fibre angle relative to the
tendon or aponeurosis) and fibre length. For example, muscles that are often
recruited to perform high force, low velocity contractions tend to have shorter
fibres and greater pennation while muscles recruited during rapid contractions
have longer fibres and lesser pennation (Burkholder et al., 1994; Kawakami et
al., 1995; Kumagai et al., 2000). Assessing inter-individual differences and
longitudinal changes in muscle architecture aids our understanding of the
muscular system. Moreover, knowledge of muscle architecture during
contraction is important for the development of realistic muscle models. Since
pennation and fibre length change during contraction, muscle models that
incorporate only architectural parameters of relaxed muscle are prone to
prediction errors. Therefore, knowledge of muscle architecture both at rest
and during contraction can allow researchers to better predict the functional
properties of human muscle.
Muscle architecture has been studied in both resting (Kumagai et al., 2000;
Van Eijden et al., 1997) and contracting (Herbert & Gandevia, 1995;
Kawakami et al., 1998; Narici et al., 1996) muscle. Such research has
examined how exercise affects architecture (Henriksson-Larsén et al., 1992;
Kawakami et al., 1993, 1995; Kumagai et al., 2000) and how architecture
changes during muscle contraction (Herbert & Gandevia, 1995; Narici et al.,
1996). While there are recognised methods of measuring muscle size and
pennation, methods for measuring fibre length are not consistent. The fibre
length of many human muscles is synonymous with the length of the fascicles
that encase fibre bundles. Since fascicles can be clearly visualised using
ultrasound imaging, fascicle length can be estimated from ultrasound
photographs.
Nonetheless, fascicle length can be estimated by two different methods. First,
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fascicle length can be estimated mathematically by the equation:
FL = MT/sin θ
where FL is the fascicle length, MT the muscle thickness, and θ the angle of
muscle pennation. Prediction of fibre length from fascicle length by this
method has been used extensively in past research (Henriksson-Larsén et
al., 1992; Kawakami et al., 1995; Kumagai et al., 2000). However, this
method incorrectly assumes that fascicles are linear within the muscle. More
recently, researchers have captured entire fascicles on ultrasound images
and used a digital curvimeter (Comcurve-8, Koizumi, Japan) to more directly
measure fascicle length (Fukunaga et al., 1997; Kawakami et al., 1998, 2000).
Here, the ultrasound images are printed onto calibrated recording film (SSZ-
305, Aloka) and the length of fascicles measured by a curvimeter. The
advantage of this method is that the curve of the fascicle is accounted for.
Thus, compared to mathematical estimation, it can be considered that the
measures of fascicle length by digital curvimeter are truer.
Unfortunately, digital curvimeter procedures have not been used in many
previous studies. Nonetheless, it is unclear how reliable current mathematical
estimation procedures are given fascicle curvature is not accounted for.
Furthermore, no research has compared fascicle length measures obtained
by the two methods. The purpose of the present study therefore was two-fold,
first to determine if a significant difference exists between fascicle length
values estimated by the two methods in both relaxed and contracted muscle,
and second to examine the reliability of the mathematical procedure relative to
the digital curvimeter procedure.
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METHODS
Measurement of Muscle Architecture
Previously published measures of fascicle length, fascicle angle (pennation)
and muscle thickness of the human gastrocnemius medialis (GM) (Kawakami
et al., 2000) were reanalysed to calculate mathematical estimates of fascicle
length. Methods used to measure muscle architecture are presented in
Kawakami et al. (2000), however a summary of the methods will be presented
here. B-mode ultrasonography was used to view images of GM in a two-
dimensional plane while six male subjects lay prone with their knee extended
and ankle at 90o. Each subject’s foot was firmly attached to an electric
dynamometer (Myoret, Asics) and the lower leg fixed to a test bench.
Measurements were taken for two conditions, with the gastrocnemius relaxed
and while performing isometric plantar flexion at a level of 50% of maximum
voluntary force. Plantar flexor torque was recorded from the output of the
dynamometer by a computer (PC-9801, NEC). It was assumed that there
was no muscle activity in the passive condition.
In both relaxed and contracted conditions, ultrasound images were obtained
from up to nine sites on GM. Longitudinal ultrasonic images of GM were
obtained at each site such that the echoes from interspaces of fascicles and
from the superficial and deep aponeuroses were visualised (Figure 1). The
ultrasonic images were then printed onto calibrated recording films (SSZ-305,
Aloka). The plane of the ultrasonogram was deemed parallel to the fascicles
since the fascicles could be followed from superficial to deep aponeurosis
(Kawakami et al., 1993). In the printed images, the length of the fascicles and
fascicle angles (pennation) were measured. Fascicle length was measured
by the use of a digital curvimeter (Comcurve-8, Koizumi) which allowed the
somewhat curved fascicles to be measured directly. Reliability of fascicle
length measures using the digital curvimeter has been previously established
(Fukunaga et al., 1997). Fascicle angle was measured with a protractor after
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a line was drawn tangentially to the fascicle at the contacting point onto the
aponeurosis. The angle made by the line and aponeurosis was measured as
the fascicle angle. At each point, muscle thickness was also measured.
Muscle thickness was defined as the distance from the junction of the adipose
and muscle boundaries to the internal aponeurosis. From measures of
muscle thickness and fascicle angle at each of the eight sites, fascicle length
was also mathematically estimated (FL = MT/sin θ, where FL is the fascicle
length, MT the muscle thickness, and θ the angle of muscle pennation).
Values for fascicle length using the two methods (digital curvimeter versus
mathematical estimation) were then compared.
A
B
Muscle/adiposeboundary
Fascicle
Aponeurosis
Musclethickness
Figure 1. Ultrasound photographs of gastrocnemius medialis under relaxed (A) andcontracted (B; 50% MVC) conditions. When contracted, muscle thickness and fasciclelength decrease compared to the relaxed state. Digital curvimeter estimates of fasciclelength are performed by tracing a fascicle from the aponeurosis to the muscle/adiposeboundary. For the mathematical method, fascicle length is estimated by the formula FL =MT/sin θ, where FL is the fascicle length, MT the muscle thickness, and θ the angle ofmuscle pennation (angle between the fascicle and aponeurosis).
B
A
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Data Analysis
Description of data
The change in fascicle length from the relaxed (A) to contracted (B) state was
designated ‘relaxed-contracted (C)’. There were eight repeated measures
(replicates) on two subjects and nine repeated measures (replicates) on the
other four subjects. Although Kawakami et al. (2000) found systematic
variation among these repeated measures, for present purposes they were
treated as randomly varying replicates. Corresponding to the curvimeter-
measured data (mFL; measured fascicle length), fascicle lengths were
estimated by the equation presented previously to construct a completely
parallel ‘estimated fascicle length’ (estFL) data set.
Data Analysis
Hierarchical (multilevel) linear regression models were fitted to the data.
(Goldstein, 1995; Hox, 1994; Snijders and Bosker, 1999). The residuals
about the fixed parts of the models (overall constant and any explanatory
factors) were modeled as varying randomly at the replicate within subject (e0ij)
and subject (u0j) levels. Restricted maximum likelihood estimates were
obtained to correct for the downward bias of maximum likelihood estimates of
variance components (Snijders and Bosker, 1999, p.56).
Three sets of three analyses (A1 to C3) were performed. For each of the sets
of relaxed (A), contracted (B) and relaxed-contracted (C) data, analyses were
performed on the measured lengths (A1,B1,C1), the estimated lengths
(A2,B2,C2) and the relationship between the measured and estimated lengths
(A3,B3,C3). The analyses A and B were variance components models in
which no explanatory variables (other than the overall intercepts) were fitted,
but in analyses C the measured values were regressed on the estimated
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values. The purpose of the analyses A and B was to estimate the
reliabilities of the measured and estimated lengths, while the purpose of the
analyses C was to estimate the ‘predictability’ of measured from the estimated
lengths.
Three subsidiary analyses (two-level variance components models) - one
each for relaxed, contracted and relaxed-contracted muscle - were performed
on the measurement-estimate difference scores in order to estimate the
extent to which the estimates were high (overestimates) or low
(underestimates) relative to the digital curvimeter measurements.
Two measures of reliability were determined for variance components
(intercept only) models: the intraclass correlation coefficient (ICC = ρ1)
measuring the reliability of a single replicate and ρ2 measuring the reliability of
the mean of n level 1 units as a measure of a level 2 unit (mean of a number
of replicates as a measure of subject fascicle length). Measures of reliability
were calculated according to the formulae presented in Snijders and Bosker
(1999, pp.24-26; n=9 in the present analyses). Two measures of explained
variance are reported for models with explanatory variables: R12 and R2
2
measuring the proportional reductions in mean squared prediction errors at
levels 1 and 2 respectively due to the explanatory variables, calculated
according to the formulae presented in Snijders and Bosker (1999, pp.102-
103).
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RESULTS
Results are presented in Table 1. An explanation of abbreviations is provided
below the table. Due to the length of the table, it is presented at the end of
this paper.
Comparison of Measured and Estimated Fascicle Length
Error-bar plots showing the subjects means and 95% confidence intervals for
the measured and estimated fascicle length are presented in Figure 2. For
relaxed, contracted and relaxed-contracted muscle, estimated fascicle length
underestimated the digital curvimeter measurements. The average
underestimation ranged from 0.43mm (1.2%) for contracted muscle, through
1.02mm (1.8%) for relaxed muscle to 1.21 (3.2%) for relaxed-contracted
muscle. These difference estimates correspond closely to the absolute
differences in the sizes of the β0ij parameter estimates from the A1-A2, B1-B2,
and C1-C2 pairs of analyses, as reported in Table 1. In no case were the
underestimates significant. t-values (parameter estimate / standard error)
ranged from 0.51 for relaxed-contracted, 0.58 for contracted and 1.03 for
relaxed muscle.
Relationship between the Estimates and the Measurements
The analyses A3, B3 and C3 found highly significant relationships between
the estimates and the measurements for each of the relaxed, contracted and
relaxed-contracted muscle fascicle lengths (the β1 estimates from Table 1).
However, although highly significant, the effects were far smaller than might
be expected of the relationship between reliable estimates and their
corresponding measurements. At the replicate level, the proportional
reductions in the mean squared prediction errors R-squared measure range
from 0.18 for relaxed-contracted, through 0.20 for relaxed to 0.22 for
contracted muscle. At the subject level, the proportional reductions in mean
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squared prediction errors were slightly higher at 0.20, 0.21 and 0.23
respectively. These relatively small proportions of the total variation among
the measurements ‘explained by’ the estimated fascicle length values are due
mostly to the variability or unreliability of these estimates.
Variance Components and Reliability
The proportions of total variance for the measurements at the subject level –
Figure 2. Mean fascicle lengths (with 95%confidence intervals) for measured ("") andestimated (ï) relaxed, contracted andrelaxed-contracted fascicle lengths.Estimated fascicle lengths were generallyshorter (not significant) and more variablethan measured fascicle lengths.
287
the intraclass correlations (ICC’s) or reliabilities of measurement at the
subject level from a single, randomly selected replicate (ρ1’s) - range from
0.75 for relaxed-contracted, 0.90 for relaxed and 0.91 for contracted muscle.
Although 0.75 is somewhat lower than ideal, this would be an acceptable level
of measurement reliability for some research. In contrast, the proportions of
total variance for estimated fascicle length at the subject level range from 0.39
for relaxed-contracted, 0.48 for relaxed and 0.60 for contracted muscle.
Apart, perhaps, for the 0.60 estimate for contracted muscle, these are less
than acceptable levels of measurement reliability, with adverse effects on
statistical power and contributing to production of inconsistent findings in
research on small samples.
These reliability estimates might be lower than the values of reliability for true
replicates because the ‘replicates’ here were expected to vary systematically
to some degree (since measures were taken from different regions within the
muscle rather than at one site). Nonetheless, the unreliability of the estimates
relative to the measurements is clear in the comparisons of their respective
amounts of replicate variation: ie 57.1 to 5.4 for relaxed, 21.4 to 3.1 for
contracted and 59.7 to 11.2 for relaxed-contracted.
Whilst single estimates provide unacceptably low levels of measurement
reliability at the subject level (ICC’s = ρ1’s), the means of a number of
replicates (ρ2’s) possess quite acceptable reliabilities. These were calculated
on the basis of 9 replicates (the mode in the present data) and ranged from
0.85 for relaxed-contracted, through 0.89 for relaxed and to 0.93 for
contracted muscle.
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DISCUSSION
Average estimated fascicle length (estFL; mathematical method) was less
than measured fascicle length (mFL; curvimeter method) for all conditions
(relaxed, contracted and relaxed-contracted muscle) with differences ranging
from approximately 0.4 to 1.2 mm (1.2 – 3.2%). None of these differences
were statistically significant. Whether underestimation of this order is
substantively important will depend upon the context of the particular
research, but the small number of subjects and low statistical power would
have influenced its significance here. In the present study however, there
was no significant difference in fascicle length measures between the two
methods.
Nonetheless, differences between estFL and mFL were greater for relaxed
than contracted muscle. While small, the difference is likely to be related to
the length of fascicles in these muscle states. Fascicles are longer in relaxed
than contracted muscle. For a given relative difference in fascicle lengths
determined by the two methods, the absolute difference will be greater than in
contracted muscle. The difference between estFL and mFL was greatest
when fascicle length change from relaxed to contracted states was estimated
(1.2 mm or 3.2% of average fascicle length). When measures of fascicle
length in relaxed and contracted muscle were used to determine the change
in fascicle length, there was a summation effect culminating in greater
differences between the two methods. Thus, for the gastrocnemius medialis
muscle, there was no significant difference between fascicle length
determined by digital curvimeter and mathematical methods, although in
muscle with long fascicles the difference between the methods would be
greater and the difference between muscles might be significant.
There was also no statistically significant difference between the measured
fascicle lengths and those predicted from the regression of measured fascicle
lengths on estimated fascicle lengths for relaxed, contracted and relaxed-
289
contracted muscle. Nonetheless, for repeated measures at each section of
the muscle, the proportional reductions in the mean squared prediction errors
R-squared measures ranged from 0.18 for relaxed-contracted, through 0.20
for relaxed to 0.22 for contracted muscle. When measures at different sites of
the muscle were averaged for each subject, the proportional reductions in
mean squared prediction errors were slightly higher at 0.20, 0.21 and 0.23
respectively. While these relatively small proportions of the total variation
among the measurements ‘explained by’ estFL were due largely to the
variability or unreliability of these estimates (see below), approximately 80%
of the total variance was left unexplained. Thus, despite mFL being predicted
well by estFL in the present study, there were clearly other factors affecting
the prediction of mFL besides estFL variability.
Reliability of the Measures
The reliability of digital curvimeter measurements at the subject level from a
single, randomly selected replicate (ρ1’s) on the gastrocnemius was
calculated. ICC’s were 0.91. 0.90 and 0.75 for contracted, relaxed and
relaxed-contracted conditions respectively. These reliability estimates might
be lower than the values of reliability for true replicates because the
‘replicates’ here were expected to vary systematically to some degree (since
measures were taken from different regions within the muscle rather than at
one site). Nonetheless, ICC’s for fascicle length determined mathematically
were 0.60, 0.48 and 0.39 for contracted, relaxed and relaxed-contracted
conditions respectively. The unreliability of estFL relative to mFL was further
highlighted by the comparisons of their respective amounts of replicate
variation: ie 57.1 to 5.4 for relaxed, 21.4 to 3.1 for contracted and 59.7 to 11.2
for relaxed-contracted. Thus, again, variability of mathematical estimation
was far greater than for the curvimeter method. Such reliability is less than
acceptable and would adversely affect statistical power and contribute to
inconsistent findings in research on small samples.
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Increasing the Reliability of Mathematically Estimated Fascicle Lengths
Whilst single estimates provide unacceptably low levels of measurement
reliability at the subject level (ICC’s = ρ1’s), the means of a number of
replicates (ρ2’s) possessed quite acceptable reliabilities. ICC’s for the
average fascicle length of a subject ranged from 0.85 for relaxed-contracted,
through 0.89 for relaxed and to 0.93 for contracted muscle. This suggests a
remedy in terms of averaging repeated measurements on the same region of
muscle (replicates) within subjects and conditions. As Table 1 shows,
although reliabilities at the replicate level (ICC = ρ1) vary between only 0.39
and 0.60, the reliabilities of averages of 9 replicates as measures at the
subject level (ρ2) range between 0.85 and 0.93. The minimum number of
replicates (nmin) required to yield a desired level of reliability at the subject
level (ρ2) given the reliability of an estimate at the replicate level (ρ1) is given
by Snijders and Bosker (1999, p.144) as,
nmin = ρ2(1-ρ1) / ρ1 (1-ρ2)
Although the power of studies could be increased by increasing the sample
size at the subject level, it may generally be more efficient to increase the
reliability of measurements at the within-subject (replicates) level (i.e. take
repeated measurements on individual subjects). This raises the general
question of how best to allocate resources between the two levels so as to
maximise research efficiency: increase subject numbers or increase the
number of repeated measurements on each subject. Snijders and Bosker
(1993) and Mok (1995) address this issue, and Snijders, Bosker and
Guldemond offer free, downloadable software (PINT = ‘power in two-level
designs’ at http://stat.gamma.rug.nl/snijders/multilevel.htm. Thus, a
comprehensive discussion of the issue will not be presented here.
In summary, for the gastrocnemius medialis muscle, there was no significant
difference between mathematical and curvimeter measures of FL. The
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mathematical method therefore provided a good estimation of fascicle
length in relaxed, contracted and relaxed-contracted conditions. Nonetheless,
there was a trend toward greater error in the mathematical method compared
to curvimeter measures (which were assumed to be accurate measures of FL)
in relaxed muscle where fascicles are long. This suggests that differences in
FL determined by the two methods would be greater for muscles with long
fascicles. The reliability of the mathematical method for measures of a single
muscle point was low. However, by taking the average of repeated measures
on subjects, reliability increased significantly. Thus researchers using
mathematical estimation of FL from muscle thickness and pennation
measurements should consider increasing the number of repeated measures
of individual subjects to improve reliability and increase statistical power.
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Relaxed muscle Model A1 1 Model A2 2 Model A3 3
Fixed effects Coefficient S.E. Coefficient S.E. Coefficient S.E. β0ij = intercept 55.52 2.87 54.51 3.16 49.58 3.46 β1 = estFLr 0.11 0.04Random effects 10
u0j : Var(subjects) 48.73 28.41 53.39 34.57 38.21 22.20 e0ij : Var(replicates) 5.38 1.12 57.12 11.91 4.95 1.03Statistics-2LL 11 260.33 370.16 254.00ICC 12 0.90 0.48ρ2
13 0.99 0.89R1
2 14 0.20R2
2 15 0.21Contracted muscle Model B1 4 Model B2 5 Model B3 6
Fixed effects Coefficient S.E. Coefficient S.E. Coefficient S.E. β0ij = intercept 37.39 2.35 36.95 2.41 32.61 2.85 β1 = estFLc 0.13 0.05Random effects 10
u0j : Var(subjects) 32.71 19.04 32.28 20.02 25.08 14.63 e0ij : Var(replicates) 3.08 0.64 21.42 4.47 2.87 0.60Statistics-2LL 11 232.31 321.77 226.48ICC 12 0.91 0.60ρ2
13 0.99 0.93R1
2 14 0.22R2
2 15 0.23Relaxed - contracted Model C1 7 Model C2 8 Model C3 9
Fixed effects Coefficient S.E. Coefficient S.E. Coefficient S.E. β0ij = intercept 32.55 2.43 31.50 2.740 27.82 2.89 β1 = est∆FL 0.15 0.06Random effects 10
u0j : Var(subjects) 34.22 20.39 38.13 25.291 27.13 16.31 e0ij : Var(replicates) 11.16 2.38 59.67 12.442 10.29 2.15Statistics-2LL 11 291.91 370.45 285.82ICC 12 0.75 0.39ρ2
13 0.96 0.85R1
2 14 0.18R2
2 15 0.20mFL: measured fascicle length (digital curvimeter)estFL: estimated fascicle length (mathematical method)r: relaxed muscle, c: contracted muscle1 Model A1: dependent variable = mFLr; independent variable = intercept only2 Model A2: dependent variable = estFLr; independent variable = intercept only3 Model A3: dependent variable = mFLr; independent variables = intercept, estFLr4 Model B1: dependent variable = mFLc; independent variable = intercept only5 Model B2: dependent variable = estFLc; independent variable = intercept only6 Model B3: dependent variable = mFLc; independent variables = intercept, estFLc7 Model C1: dependent variable = m∆FL; independent variable = intercept only8 Model C2: dependent variable = est∆FL; independent variable = intercept only9 Model C3: dependent variable = m∆FL; independent variables = intercept, est∆FL10 Variance components and their standard errors (SE)11 –2LL = minus 2 loglikelihood = deviance12 ICC = intraclass correlation coefficient = ρ1 = reliability of a single replicate13 ρ2 = reliability of mean of 9 replicates as measure of a subject
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14 R12 = proportion of replicate variance explained
15 R22 = proportion of subject variance explained
Table 1. Results of the multilevel regression analysis for relaxed (A), contracted (B) andrelaxed-contracted (C) conditions. Fascicle length calculated by curvimeter (1) andmathematical (2) methods are indicated in the ‘β0ij = intercept’ row and are in the units ofmillimetres. For all contraction states, mathematical estimates were slightly, but notsignificantly, lower than curvimeter estimates. Variance of measures at one site on themuscle were higher for mathematical estimates [e0ij : Var(replicates)], although variancecalculated on the mean of repeated measures (ie at the subject level) was relatively similarbetween the methods [u0j : Var(subjects)]. Reliability of fascicle length estimates at individualsites using the mathematical method were low (ICC = ρ1) although reliability was improvedsubstantially when repeated measures were averaged (ρ2). Models A3, B3 and C3 show theprediction of measured fascicle length (mFL; curvimeter estimates) from estimated fasciclelength (estFL; mathematical estimates) with proportions of replicate and subject varianceexplained (R1
2 and R22 respectively). There was no statistically significant difference between
measured fascicle lengths and those predicted from estimated fascicle length although theproportion of variance explained was low.
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REFERENCES
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Fukunaga, T., Ichinose, Y., Ito, M., Kawakami, Y., & Fukashiro, S. (1997).
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Goldstein, H. (1995). Multilevel Statistical Models. 2nd Edition London:
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Henriksson-Larsén , K., Wretling, M.-L., Lorentzon, R., & Öberg, L. (1992). Do
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Kawakami, Y., Abe, T., & Fukunaga, T. (1993). Muscle-fiber pennation angles
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Kawakami, Y., Abe, T., Kuno, S., & Fukunaga, T. (1995). Training-induced
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functional features of human triceps surae muscles during contraction.
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(2000). Sprint performance is related to muscle fascicle length in male 100-m
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APPENDIX G
FORWARD HACK SQUAT DATA COLLECTION SCHEMATIC
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1
2
3
4
6
5
7
8
9
10
11
13
12
14
15
1618
17
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Diagram(ICAM)
Description/definition
Setpoint: implements voltage reference, DC voltage – (1) 10 V, (2)0 V.Analog output: directs data stream to an output on an analogmodule, here it powers the load cell (3) or position transducer (4).Analog input: receives external signals, e.g. fromtransducers/potentiometers. (5) received force input, amplifier gain= 300 volts/volt, DC offset range = 127. (6) received position input,amplifier gain = 10 000 volts/volt, DC offset range = 127.Zero order hold: set to hold value in input data stream [force (7)or position (8)] until next trigger (see below).Subtraction: subtracts two input values (e.g. a raw input from aheld [see above] value).Multiplication: multiplies two input values.
Variable amplifier: amplifies input data stream by a specifiedvalue using a potentiometer while the system is running. (9)calibrate force, gain = 0.742 units/unit, (10) calibrate position, gain= 1.02 units/unit.Display trace: displays a moving trace of the values of a datastream. (11) force trace, (12) position trace.Numeric display: displays a value in numeric form.
Peak detector: measures the peak value of a signal, can be resetto a specified level (usually zero) before each data acquisitionperiod (trial). (13) detects peak force, resets to zero.Square wave generator: provides a square wave at frequencyproportional to the voltage at its input, allows setting to 0 V (as inthis case) to provide 0 Hz. (14) oscillator calibration = 10 Hz/unit,frequency with 0V input = 3 Hz, Peak to peak amplitude = 10 units,zero offset.Check box or trigger: triggers an event such as data collection orreset. (15) collect data.Pulse generator: outputs pulse of specified duration. Used here tocollect 400 samples of force and position data over a 4 s timeperiod.Variable set point: implements a floating point variable voltagereference, allows reference voltage to be altered while program isrunning. (16) set to ‘angle = 51 deg’.Function: converts X to Y. (17) convert degrees to radians, (18)cos function to calculate vertical component of force.
300