Quantifying the Movement and the Influence of Load

QUANTIFYING THE MOVEMENT AND THE INFLUENCE

OF LOAD IN THE BACK SQUAT EXERCISE

MARK R. MCKEAN, PETER K. DUNN, AND BRENDAN J. BURKETT

Australian Institute of Fitness Research, University of Sunshine Coast, Queensland, Australia

ABSTRACT

McKean, MR, Dunn, PK, and Burkett, BJ. Quantifying the

movement and the influence of load in the back squat exercise.

J Strength Cond Res 24(6): 1671–1679, 2010—The squat is

used extensively in strength and conditioning, physical therapy,

rehabilitation, and fitness programs. However, the movement

pattern of the hip and knee is still relatively unknown, in

particular, the timing of when maximum angles is reached. The

purpose of this study was to quantify the hip and knee

movements of the squat and establish if load alters these

movements. Twenty-eight subjects (16 men and 12 women)

performed 2 sets of 8 squats. Load was applied in random

order as no additional weight (body weight [BW]) or an

additional load of 50% of the subject’s weight (BW+50%).

Joint angles and time for hip and knee, as well as forward knee,

displacement in the descent and ascent phases were measured

with significance at p, 0.05. Regardless of gender, phase, and

load, all subjects achieved their maximum hip and knee angles

within 2% of the deepest position. Load significantly increased

the flexion angle at the hip and knee joints in men. The knees

movement forward of the toes ranged from 63.8 to 64.7 mm in

men and 93.2 to 96.6 mm in women. A significant difference

in the timing of when the maximum forward knee movement

occurred was observed because of gender. The overriding

factor for the practical prescription of squat technique was

regardless of load, gender, or phase; the maximum angles of the

hip and knee are reached almost simultaneously at the bottom

of the squat. Furthermore, for all subjects, the knee moved

forward of the toes when squatting with men reaching their

maximum forward knee position around 84% of the descent

phase, whereas this occurred for women around 93%.

KEY WORDS technique, hip, knee, knee movement, pattern

INTRODUCTION

The squat exercise is commonly used by strengthcoaches, health professionals, physical therapists,and fitness trainers in exercise programs. The squathas been generally categorized into 3 groups:

partial squats, parallel squats, and full or deep squats (8,31,37).Partial squats represented as a squat less than parallel, parallelsquats indicated by thighs being parallel to the floor, and fullsquats indicated by a deeper squat than parallel thighs, allof which have a broad range of applications across manyenvironments. The most common squat cited in the literatureto date is the parallel squat (19,25,34,37), but because of thevariety of squat depths cited in the literature, any comparisonof joint movements and timing from these studies is difficult.Previous research on squat movements has predominantlyfocused on the movements of the knees in isolation to the hipfor a rehabilitation focus, such as the forces at the knees(4,27,35), knee stability (7,13), and muscle recruitment of thethigh (6,22,33). No previous studies have provided a completepicture of the hip-knee movements and timing in squattingbecause they have not been examined as part of a coordinatedglobal movement. Knee angles have been shown to reach asmuch as 40� flexion (9) and hip angles up to 34�(37), yet bothknee and hip angles have been reported as maximums onlywith no mention as to the timing of when these maximumangles occur during the descent or ascent phases of the squat.Young athletes, people new to strength training, and those

recovering from injury are taught to squat as part of theexercise regimen with the aim of increasing the loads used forsport-specific gains (32,36) or developing better muscularcontrol to support the knee after injury (22,26). Coaches,therapists, and trainers who work with these groups ofpeople need to have an understanding of the coordinatedpattern of squatting to develop a new pattern of movement orretrain the desired pattern of movement, which may changeas a result of injury (21). The coordination of joints and thetiming of these movements in squatting need to be quantifiedto provide a clearer understanding of the squat movementpattern when coaching this exercise.Multiple loading parameters have also been used in

previous squat research ranging from body weight (BW)squats to 1 repetition maximum (1RM). In 2005, Scaglioni-Solano et al. (31) studied movement patterns of squats using

Address correspondence to Mark R. McKean, [email protected] funding was received for this research project.

24(6)/1671–1679

Journal of Strength and Conditioning Research� 2010 National Strength and Conditioning Association

VOLUME 24 | NUMBER 6 | JUNE 2010 | 1671

BWonly, finding that deeper squatting shifted the effort fromthe knee joint to the hip joint and after 65�knee bend, the hipand knee movements became more similar in behavior.Abelbeck (2) used BW squats to study the biomechanics oflinear motion squats reporting segment mass movements andproviding feedback on hip and knee positions. Finally,Dionisio et al. (11) applied BWas the squat load to investigatethe kinematic, kinetic, and electromyographic pattern indownward squatting. Submaximal loads have been used inresearch to minimize fatigue (6) and use a repetition rangesimilar to those common in training (15), whereas 1RM loadsup to 2.5 times a subject’s BW (25) have been used to studybehavior at a subject’s strength limits. To determine if loadinfluences squat technique, loads that allow a number ofrepetitions to be performed without fatigue and provide forsafe progressions need to be used, so the repetitions capturedcan be analyzed for consistency and coordination.Strength training exercises can be broken into the phases

of descent and ascent. To the author’s knowledge, the dif-ferences, if any, in the movements of the hip and knee in eachphase is not mentioned in the literature, despite the fact thatthe squat requires both up and down phases, which sub-sequently requires different concentric and eccentric muscleinnervations. Specific knee angles or the parallel position ofthe thighs have been used as the finish point for the descentphase of the squat, yet this restriction may limit the user’snatural movement pattern of the squat. A more appropriatemeasure of determining squat depth would be the verticaldisplacement of the pelvis to set the start and completion ofeach phase. In exercise prescription, changing training tempofor each phase is commonly used to create a training emphasis(1,20), yet there has been little research to determine if thereare changes in joint coordination in the different phases,which may ultimately alter the muscles involved and theinfluence of adjusting eccentric and concentric speeds.Because of the different contraction types during the decentand ascent phases, each phase should be quantified sepa-rately and the vertical displacement was used to set top andbottom positions of the squat.Forward horizontal movement of the knees over the toes

during the squat has been associated with increased forces atthe knee joint and suggests that the knees should be restrictedto a position behind the vertical line of the toes to protectthe knees (30). The study by Fry et al. (19) showed that thetechnique of restricted forward knee movement adjusted thesquat movement and produced more anterior lean and anincreased hip angle when compared with the unrestrictedsquat technique. Forward knee movement in the back squatneeds further examination to understand its impact on jointcoordination and the relative timing in squatting movements.There is also a contradiction in previous studies regarding

differences in the patterns of movement between men andwomen. Some studies show that there had been a significantdifference in these patterns (29,39), and others have shownno significant differences between genders (3,10). To address

these issues, the specific aims of the current study were toquantify the timing and movement relationships of the hipand knee joints for the back squat exercise and changes tothese patterns because of (a) changes in load, (b) the ascentand descent phases, and (c) gender.

METHODS

Experimental Approach to the Problem

A 3-dimensional analysis of the lower limbs and torso wasconducted as subjects completed 2 sets of 8 repetitions of theback squat exercise. The independent variables were load,phase, and gender. The dependent variables were hip angle,knee angle, knee forward position, and timing. The 3-dimensional analysis machine allows the timing and move-ment of the hip and knee joints to be measured simulta-neously during both the descent and ascent phases ofmovement. Subjects performed 8 squats with 2 different loads(BW with no external load, and BW + 50% of BW as anexternal load); the order for each subject was randomized. Foreach load, each subject did 8 squats (with 90- to 120-secondrecovery between each set); data were only collected for 3 ofthese squats, but the 3 selected for data recording were notmade known to the subjects.In random order, the load for each set was either BW (BW,

no external load) or BW plus 50% BW load (BW+50%).

Subjects

Twenty-eight subjects with at least 1-year experience in usingthe back squat as an exercise in their training routinevolunteered for the study (Table 1). Subjects were either intheir final year of study to become a personal trainer oralready working as an accredited personal trainer. Subjectshad been performing squats as an exercise in their strengthand conditioning training programs at least twice a week fora minimum of 12 months. Subjects were informed of theexperimental risks, and written informed consent wasobtained under the guidelines approved by the universityhuman research and ethics committee before any experi-mental testing. All subjects indicated that they had noexisting conditions or history of musculoskeletal injury.

Procedures

Total body mass was measured to the nearest 0.01 kg withcalibrated electronic scales (TI BWB-600P, Digital PersonalScale; Wedderburn Pty Ltd, Willawong, Australia), andstanding height of individual subjects was measured to thenearest 1 mm with a portable stadiometer (Telescopic MetalHeight Scale [PE063]; Mentone International, Moorabin,Australia) The laboratory is a nationally accredited facility forathletic testing. Real-time kinematic motion of the lowerlimbs and torso was collected at 120 Hz by a 3-dimensionalmagnetic tracking device (Motion Monitor, Version 6.50.0.1;Innovative Sports Training, Chicago, IL, USA). Eightmagnetic sensors were placed on anatomical segments asdescribed in Table 2. Validation of the system was confirmedagainst standardized reference measures, and the variation

1672 Journal of Strength and Conditioning Researchthe TM

Influence of Load in the Back Squat Exercise

was less than 0.5� and within 0.0034 m. Three-dimensionalmagnetic tracking has been shown to be more accurate than2 dimensions and has been previously validated (28).Thepelviswas digitized using theBellmethod,whichuses the

anterior superior iliac spine (ASIS) width to determine hip jointcenter and pelvic girdle structure. The knee and ankle jointcenters were determined using the centroid method. The hipjoint angle is the angle between the alignment of the pelvis andline between the hip and knee joint centers. The knee joint anglebeing the angle between the lines connecting the joint centers ofthe hip to knee and knee to ankle as defined in previous studies(2,6,19,31). The most anterior aspect of the patella was digitizedwith a 3-dimensional landmark referenced to the knee jointcenter, allowing it to be tracked with regards to forward kneemovement in the sagittal plane (19).The subjects warmed up as per their usual routine for

strength training, and then with the sensors attached, thesubjects performed a warm-up set of squats. The width ofstance was controlled with the inside distance between thesubject’s heels, the same as the pelvic width measured fromright ASIS to left ASIS (15), using skeletal goniometers (TTMBone Calliper, PE054; Mentone International). The feet werealigned parallel to the sagittal plane, that is, toes pointedstraight ahead, and the knees were free to move in any position.

To determine if load influencedmovement patterns in a safeand repeatable manner, the loads of BW and a submaximalload of BW + 50% (BW+50%) were chosen. These 2 loadsallowed multiple sets of 8 repetitions without fatigue (12),a range of repetitions and loading parameters similar to thetraining environment they would be exposed to, and thecapture of 3 blind repetitions for analysis.Todevelop50%load,analuminumOlympicbarandassociated

weights was placed into a standard position across the uppertrapezius and superior aspect of the spine of scapula, the handsplacedoutside shoulderwidth inapalm forwardgrip.Astandard-sizedOlympicbarconstructedfromaluminum(AustralianBarbellCompany, Mordialloc, Victoria, Australia) was used becausenormal ferrous metals in traditional bars cause interference withthe magnetic fields of the magnetic tracking device.The subject assumed the setup position, and thewidth of feet

was established using a steel measuring ruler and marks placedon the floor. Starting in an upright position, the subjectdescended to the lowest point they felt in control andcomfortable, with no limit placed on the depth of the squat.

TABLE 1. Subject characteristics (mean and SD).

Subjects Age (yr) Weight (kg) Height (cm) ASIS width (cm)

Women (n = 12) 24.2 (6.5) 62.1 (7.9) 167.1 (4.9) 24.4 (2.2)Men (n = 16) 24.3 (5.1) 83.2 (12.2) 179.5 (6.5) 25.5 (1.3)Combined (n = 28) 24.2 (5.7) 74.1 (14.9) 174.2 (8.5) 25.0 (1.8)

ASIS = Anterior Superior Iliac Spine.

TABLE 2. Position of sensors for 3-dimensionalmagnetic tracking device.

Sensor Anatomical segment

1 Stylus to digitize the subjects dimensions2 Thorax (the C7-T12 junction)3 Lumbar (dorsal surface of T12-L1 junction)4 Sacrum (dorsal surface of L5-S1 junction)5 Left Thigh (anteromedial aspect of upper

thigh)6 Right Thigh (anteromedial aspect of upper

thigh)7 Left Shank (anteromedial aspect of the

Tibia shaft)8 Right Shank (anteromedial aspect of the

Tibia shaft)

Figure 1. A digital of a man squatting with a warm-up load.


Journal of Strength and Conditioning Researchthe TM

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The squat was performed ac-cording to the National Strengthand Conditioning Association(NSCA) position guidelines onsquats and monitored by themain researcherwhoisanNSCACertified Strength ConditioningSpecialist coach at the elite level.A digital of a typical man squat-ting with a BW+50% load isshown in Figure 1.One squatwas completewhen

the subject returned to the orig-inal upright starting position. Ifthere was a safety concern, or thesubjectwishedtoceasetheaction,2 spotters were positioned tosupport the subject. The subjectexhaledontheascentand inhaledon the descent, and each subjectwas given 90- to 120-secondrecovery between each set. Themiddle 3 repetitions of each setwere collected for analysis withthe subject being blind to whichrepetitions were collected for theproject. All angles are orthopedicanglesof the linesconnecting thedigitized jointcentersof thehip,knee, and ankle. The hip angle was defined as the anterior anglebetween the trunk and the thigh; the knee angle was defined asthe posterior angle between the thigh and the lower shank(Figure 2). Forward knee movement (measured in the sagittalplane) was defined as the horizontal distance the anterior aspectof the knee moved with respect to the front of the shoes.If the knees remained behind the toes, this was reportedas a negative score. If the knee moved anterior to that ofthe vertical line drawn from the front of the shoe, the scorewas positive.

The time for each phase (decent and ascent) was normalized,with the starting point at the top of the squat (highest verticaldisplacement of the sacrum) represented as 0%, whereas thedeepest part of the squat (lowest vertical displacement ofthe sacrum) represented as 100%, regardless of the phase ofthe movement.

Statistical Analyses

A total of 6 different responses were analyzed (maximum hipangle, the time at which the maximum hip angle occurred,maximum knee angle, the time at which the maximum knee

Figure 2. Angle conventions used for analysis.

TABLE 3. The maximum angle for the hip joint and normalized time for when this occurred (mean and SE) during thedescent and ascent phases of the back squat, for body weight load and body weight + 50% body weight.

Description

Descent phase Ascent phase

Body weight Body weight + 50% Body weight Body weight + 50%

MenHip max angle (degrees) 77.5 (3.4)* 73.6 (3.5)* 77.4 (3.5)* 73.6 (3.5)*Time max hip (%) 98.4 (0.4) 98.2 (0.4) 98.9 (0.1) 98.1 (0.4)

WomenHip max angle (degrees) 77.2 (1.6) 76.3 (1.2) 77.3 (1.6) 76.3 (1.2)Time max hip (%) 98.6 (0.2) 98.7 (0.2) 98.9 (0.1) 98.9 (0.1)

*Significant difference (p, 0.05) between the maximum hip angles achieved in both phases for men when comparing the 2 loads.



angle occurred, the maximum knee forward position relativeto the toes, and the time at which the maximum knee forwardposition relative to the toes occurred). Each of these 6responses was analyzed separately for differences amonggender (men or women), phase (ascent or decent), and load(BWor BW+50%). The results (Tables 3–5) are presented asmean and SE analyzed for gender (men or women), load(BW or BW+50%), and phase (ascent or decent). Intraclasscorrelation coefficients (ICCs) were calculated to assess thereliability of the repeated measures using the Bland andAltman method (5). Intraclass correlation coefficient valuesless than 0.4 represented poor reliability, 0.4–0.7 fair reli-ability, 0.70–0.90 good reliability, and greater than 0.9excellent reliability (16). Sixty-six percent of ICC valueswere in the excellent category (above 0.9) and 25% in thegood category (above 0.7), giving a total of 91% of ICC values

above 0.7, showing good reliability of the data. Statisticalinterpretation focused on the main effects, and the thresholdfor statistical significance was set to p # 0.05. Linear mixedmodels were used to model the data using subjects as randomeffects. Models were fitted individually with one responseand one explanatory variable (gender, phase, or load) as afixed effect. Differences were then detected using the p valuesfrom the analysis of variance F tests on the correspondingfixed effect.The ICC values for the dependent variables are included in

Table 6.

RESULTS

The maximum hip joint angle and normalized time for whenthe maximum occurred during the descent and ascent phasesfor both men and women are presented in Table 3.

TABLE 4. The maximum angle for the knee joint and normalized time for when this occurred (mean and standard error)during the descent and ascent phases of the back squat, for body weight load and body weight + 50% body weight.

Description



MenKnee max angle (degrees) 64.6 (2.2)*† 59.1 (2.0)*† 63.4 (2.3)*† 59.2 (2.0)*†Time max knee (%) 99.2 (0.3) 99.0 (0.2) 98.9 (0.1) 99.0 (0.2)

WomenKnee max angle (degrees) 72.6 (3.3)† 72.4 (2.9)† 72.7 (3.3)† 72.5 (2.9)†Time max knee (%) 99.3 (0.2) 98.9 (0.3) 98.7 (0.2) 98.7 (0.2)

*Significant difference (p, 0.05) between the maximum knee angles achieved in both phases for men when comparing the 2 loads.†Significant difference (p , 0.05) between the maximum knee angles achieved in both phases when comparing genders.

TABLE 5. The maximum knee forward movement distance and normalized time for when this occurred (mean and standarderror) during the descent and ascent phases of the back squat, for body weight load and body weight +50% bodyweight.

Description



MenKnee toe distance (mm)* 67.4 (7.4) 72.1 (6.5) 63.8 (6.9) 74.9 (6.8)Time knee toe (%)† 82.5 (3.5) 87.5 (2.8) 84.2 (2.1) 81.4 (2.5)

WomenKnee toe distance (mm)* 96.6 (9.0) 85.7 (12.6) 93.2 (8.9) 83.0 (12.4)Time knee toe (%)† 92.1 (2.0) 94.1 (1.4) 93.7 (1.6) 94.9 (1.0)

*Significant difference (p , 0.05) between the maximum forward knee movement achieved in both phases when comparinggenders.

†Significant difference (p , 0.05) between the time of the maximum forward knee movement achieved in both phases whencomparing genders.



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Loadwas significantly associatedwith the squat technique inmen with the BW+50% squat reducing the hip and the kneeangles, when compared with the BW squat. There was nosignificant change in the time for when the maximum angleswas reached because of different loads. There was no statis-tically significant difference in themaximum angles achieved inthe BW squat at the hip joint for men and women, withdifferences of 0.1� between phases and 0.3� between genders.However, with an increased load of BW+50%, men achieveda maximumhip angle 3.9� deeper, and the ascent hip angle was3.8� deeper than women.The maximum knee joint

angle and normalized time forwhen the maximum occurredduring the descent and ascentphases for bothmen andwomenare presented in Table 4.Gender had a significant in-

fluence on knee angle achievedwith men reaching greater kneeflexion angles for both phases,when compared with women.However, the timing of whenmaximum knee angles wereachieved was not significantlyassociated with gender. Kneemovements also produced sig-nificant results in regards tochanges brought about by theincreased load of BW+50%.The descent knee maximumangle was 5.5� deeper, and the

ascent knee angle was 4.2� deeper for BW+50% squats.Further, for the descent and ascent phases, and for BW andBW+50% load, men achieved significantly deeper angles ofknee flexion compared with women. Finally, when compar-ing the difference between the maximum angles at the hipand the maximum angles at the knee, women differed bya maximum of 4.6�, whereas men differed by a minimumof 12.9�.The maximum knee forward movement and normalized

time for when the maximum occurred during the descent

TABLE 6. ICC values for dependent variables.*


BW BW+50% BW BW+50%

MenHip angle 0.98 0.99 0.99 0.99Hip time 0.86 0.91 0.91 0.85Knee angle 0.98 0.99 0.99 0.99Knee time 0.90 0.85 0.90 0.90Forward knee position 0.98 0.99 0.97 0.98Forward knee time 0.94 0.85 0.90 0.83

WomenHip angle 0.97 0.96 0.97 0.97Hip time 0.53 0.49 0.57 0.41Knee angle 0.92 0.98 0.99 0.98Knee time 0.75 0.85 0.78 0.87Forward knee position 0.99 0.99 0.99 0.99Forward knee time 0.88 0.88 0.80 0.91

*BW = body weight; BW+50% = body weight plus 50% body weight load.

Figure 3. Sample male hip and knee movement in a body weight plus 50% body weight load squat.



and ascent phases for both men and women are presentedin Table 5.Both men and women showed a forward horizontal move-

ment of the knee. This distance was significantly different forgender in both phases. Therewas also a significant difference inthe time of when themaximum forward horizontal movementof the knee was achieved because of gender, with menachieving the maximum distance at less depth in the squat inboth phases. Men significantly increased the forward move-ment of the knees during the BW+50% squats compared withBW, whereas women significantly reduced the forward kneemovement during the BW+50% squats compared with BW.When subjects squatted with no restriction on knee angles,

forward knee movement, or depth of the squat, all subjectsreached their maximum hip and knee angles within 2% of thedeepest part of the squat, in both descent and ascent phases,regardless of load and gender. A screen shot of a typical hipand knee movement comparison is shown in Figure 3.

DISCUSSION

The specific aims of this study was to first quantify the timingand movement relationships of the hip and knee during theback squat exercise, then to consider any changes to thesemovements with respect to changes in load, the ascent anddescent phases, and gender.Squatting depth has long been a contentious issue in the

practical training environments, and the safe depth ofsquatting, commonly reported as being a parallel squat, isusually indicated by the thigh being parallel to the floor (14).Deep squats are cited less often as a recommended technique.The freely selected squat depth within the current studywould categorize the squats performed in this study as deep,and this greater range of movement provides the participantwith the greatest freedom to move naturally.The significant differences of both the hip and the knee

angles achieved by men with respect to changes in loadsuggest that men differ in the manner in which their lowerextremity absorbs and transfers load through their musclesand joints when performing squats. These results show that asthe loads increase, men’s hip and knee angles increase toaccommodate the loads, thus altering the relative angles ofthese 2 key joints yet maintaining the timing of when thesemaximum angles occur. The low standard of error in thetiming of when the maximal angles were reached reinforcesthe consistency of the timing and the patterns of movementachieved across both loads and gender and suggests that thisis a dominant overriding component of the squatting patternof movement, which is somehow maintained at all times.Women on the other hand produced almost identical hip

and knee angles for BWsquats and BW+50% squats, and thedescent and ascent phases of the squat, suggesting a morecoordinated squatting movement. No similar studies werefound in the literature that compared these variables. Staturemay be considered as an influence on this changed behavior.Men are taller, and this may account for the altered hip-knee

movements when compared with women. Research hasshown that a subject’s height, tibial length, and femur lengthaccount for 77.8% of the explained variances in a subject beingable to keep their heels flat when squatting (18). To keep theheels flat, a subject would need to alter the hip-kneemovements to maintain balance. This alteration in move-ments may be similar to the manner in which men in thecurrent study altered their hip-knee actions.The similarities in angles achieved by women at the hip and

knee joints also suggest that women tend to be moresynchronized for the hip-knee interjoint–coordinated move-ment of squatting. This is demonstrated as the hip and kneejoints differ by 4.6� or less in both loads and phases in women,compared with men whose hip and knee joint angles differedby as much as 14.5�. This finding is also supported byLindbeck and Kjellberg (24) who suggest that women havebetter hip-knee joint coordination for lifting tasks, whencompared with men. Although women maintained similarangles at the hip and knees, the pattern of squatting for menshows that they increase the angles at the hip and kneejoints to perform the back squat when loads are increased toBW+50%. These increased angles at the hip and knee sug-gest that the heavier loads allow men to squat deeper, whichmay reflect the increased strength levels of men or the factthat the 50% load was a lower percentage of the men’s 1RM.When squatting with BW, only there was no difference

in the timing of the hip and knee joints between men andwomen. There was, however, a significant difference in theknee flexion angle between genders, which highlights adifference in movement patterns across genders and supportsother studies (17,23,24,38). As the load increased, only menchanged their degree of flexion at each joint, which furtherreinforces this finding.Knee position, relative to the toes, is also a contentious

topic when performing squats. Very little scientific data havebeen recorded regarding the distance the knees moveforward, with respect to the feet during squats. The currentstudy found that subject’s knees did naturally move forwardof the front of the foot by a considerable margin. Only1 reference was found measuring forward knee movement insquatting (11), and forward knee movement was measuredfrom the start of the squat and not with respect to theposition of the front of the foot. Any comparison with thecurrent study is difficult because the previous study allowedsubjects to only half squat and restrictions were placed on theposition of the trunk relative to a wall in front of the subjects.Any restriction placed on the knee movement in the squat

exercise will result in mechanical changes at the hip and knee(19). The results from the current study could indicate a truerrelationship of the hip-knee simply because the subjects werenot restricted in knee movement or squat depth and per-formed the squat in a way that was most comfortable forthem as individuals, resulting in a forward knee movementappropriate to them as individuals. The timing of the maxi-mum knee forward position was before that of the maximal



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angles of the hip and knee. This mechanism has not beenfound in the literature and indicates that the knees may in factbecome more static once this maximum forward positionwas reached. In all cases except men with BW+50%, themaximum forward knee position was greater in the descentthan for the ascent. Under BW+50% load, men achieveda greater maximum forward position in the descent than inthe ascent phase, which may reflect the increased angles offlexion achieved at the hip and knee for the increased load.The knees of both men and women moved forward

horizontally past the vertical line of the front of the foot;however, women produced a greater forwardmovement thanmen when squatting. It should also be noted that for allsubjects, the distance the knees moved forward during thesquat produced the greatest variation of all the data reported.This shows that the forward knee movement in squattingproduces a range of very individual results and suggests thatthis is a secondary function in squatting that occurs becauseof some other movement. Added to these differences, thecurrent results also found that the time for when thesemaximum forward positions were reached differed signifi-cantly. In the BW+50% squats, men reached their maximumforward knee position 6.6% sooner in the time of the descentand 13.5% later in time of the ascent compared with women.The current research has shown differences in lower limbkinematics across gender, with men reaching their maximumforward knee position much sooner than their hip and kneeangles reach their maximum angle of flexion. Conversely,women on the other hand reach theirmaximum forward kneeposition much closer to the time at which their hip and kneeangles also reach their maximum, confirming that womentend to be more synchronized in the squatting movement.

PRACTICAL APPLICATIONS

This research showed that there were 2 key aspects tosquatting: (a) the timing of the hip and knee maximum anglesand (b) the forward knee movement past the toes.This research found that performing the squat with BWand

submaximal loads establishes a very definite timing of jointmaximum angles and coordination of the lower extremities,that is, hip joint, knee joint, and forward knee movement. Thetiming of when the hip and knee reach their maximum angleswith BWand +50% BW loads shows that experienced squatperformers with submaximal loads coordinate the hip andknee joints to reach maximum angles of flexion within 2% ofthe maximum descent position, which may be a controllingfactor in performing the squat. This study may provideadditional cues and timing knowledge for improving teachingand monitoring of squat techniques as by establishing keyguidelines on movement coordination of the hip and kneethat could be used as a standard for squatting.Care should be taken when prescribing exercises to men

and women because significant differences in the manner inwhich men and women perform the squat and how theyadjust these squat movements with an additional load of

BW+50% were found. As the load increased, men squatdeeper achieving increased hip and knee angles. This resultsuggests that under the heavier load of BW+50%, men stillcontrolled joint coordination timing but adjusted the rate atwhich the movement occurred at each joint to do so. Womenon the other hand produced almost identical hip-kneemovements for BW squats and BW+50% squats, suggestinga more controlled and coordinated squatting movements.This joint coordination timing appears to be maintainedregardless of load and gender and suggests that it is a keyaspect to squat movement pattern.In the practical setting, coaches and trainers should be

aware of the differences between men and women inadjusting hip and knee movements to handle additionalloads. Allowing for the adjustments made by men, the timingelement of these maximal angles still appears to bemaintained, and this could be used to visually assess thecoordination of the squat movement. If the timing of whenmaximum angles are reached appears to be significantlydifferent, this research suggests that they may have an alteredmovement pattern and may need to have further coaching onsquat technique to ensure that maximum angles are reachedalmost simultaneously near the bottom of the squat.The current study also showed that subjects with at least

1-year squatting experience tended to squat deep when notlimited by instruction and allowed their knees to moveforward over the front of the feet during the performance ofthe back squat. This research shows that to perform a deepsquatting action, subjects will not restrict the forwardmovement of the knees over the toes, instead allowing themtomove forward as required as if the forward knee movementis a secondary element of squatting, which relies on othermovements to control its action. In developing athletes,those with little strength training experience, and peopleperforming squats as part of a rehabilitation process, this studysuggests that coaches and trainers should allow the kneesto move to a position in squatting where the hip andknee coordination is maintained rather than restricting theknee any specific alignment and causing a change to thehip-knee coordination.

REFERENCES

1. Aagaard, P, Simonsen, E, Andersen, J, Magnusson, S,Halkjaer-Kristensen, J, and Dyhre-Poulsen, P. Neural inhibitionduring maximal eccentric and concentric quadriceps contraction:Effects of resistance training. J Appl Physiol 89: 2249–2257, 2000.

2. Abelbeck, KG. Biomechanical model and evaluation of a linearmotion squat type exercise. J Strength Cond Res 16: 516–524, 2002.

3. Albert, WJ. Are males and females similarly consistent in theirrespective lifting patterns? Theor Issues Ergon Sci 9: 347–358, 2008.

4. Beynnon, BD, Johnson, RJ, Fleming, BC, Stankewich, CJ,Renstrom, PA, and Nichols, CE. The strain behavior of the anteriorcruciate ligament during squatting and active flexion-extension:A comparison of an open and a closed kinetic chain exercise. Am JSports Med 25: 823–829, 1997.

5. Bland, M and Altman, D. Measurement error and correlationcoefficients. BMJ 313: 41–42, 1996.



6. Caterisano, A, Moss, RF, Pellinger, TK, Woodruff, K, Lewis, VC,Booth, W, and Khadra, T. The effect of back squat depth on theEMG activity of 4 superficial hip and thigh muscles. J Strength CondRes 16: 428–432, 2002.

7. Chandler, TJ, Wilson, GD, and Stone, MH. The effect of the squatexercise on knee stability. Med Sci Sports Exerc 21: 299, 1989.

8. Colker, CM, Swain, MA, and Lynch, L. Effects of full verses parallelsquats on quadriceps muscular hypertrophy in healthy male athletes.Med Sci Sports Exerc 34(5 Suppl. 1): 81, 2002.

9. Dahlkvist, NJ, Mayo, P, and Seedhom, BB. Forces during squattingand rising from a deep squat. Eng Med 11: 69–76, 1982.

10. Decker, M, Torry, M, Wyland, D, Sterett, W, and Richard Steadman,J. Gender differences in lower extremity kinematics, kinetics andenergy absorption during landing. Clin Biomech (Bristol, Avon)18: 662–669, 2003.

11. Dionisio, VC, Almeida, GL, Duarte, M, and Hirata, RP. Kinematic,kinetic and EMG patterns during downward squatting.J Electromyogr Kinesiol 18: 134–143, 2008.

12. Donnelly, DV, Berg, WP, and Fiske, DM. The effect of the directionof gaze on the kinematics of the squat exercise. J Strength Cond Res20: 145–150, 2006.

13. Escamilla, RF. Knee biomechanics of the dynamic squat exercise.Med Sci Sports Exerc 33: 127, 2001.

14. Escamilla, RF, Fleisig, GS, Lowry, TM, Barrentine, SW, andAndrews, JR. A three-dimensional biomechanical analysis of thesquat during varying stance widths. Med Sci Sports Exerc 33: 984,2001.

15. Escamilla, RF, Fleisig, GS, Zheng, N, Lander, JE, Barrentine, SW,Andrews, JR, Bergemann, BW, and Moorman, CT III. Effects oftechnique variations on knee biomechanics during the squat and legpress. Med Sci Sports Exerc 33: 1552, 2001.

16. Fleiss, J. The Design and Analysis of Clinical Experiments. New York,NY: John Wiley and Sons, 1986

17. Ford, KR, Myer, GD, Toms, HE, and Hewett, TE. Gender differencesin the kinematics of unanticipated cutting in young athletes. Med SciSports Exerc 37: 124, 2005.

18. Fry, A, Housh, T, Hugjes, R, and Eyford, K. Stature and flexibilityvariables as discriminators of foot contact during the squat exercise.J Appl Sport Sci Res 2: 24–26, 1988.

19. Fry, AC, Smith, JC, and Schilling, BK. Effect of knee position onhip and knee torques during the barbell squat. J Strength Cond Res17: 629–633, 2003.

20. Higbie, E, Cureton, K, Warren, G, and Prior, B. Effects of concentricand eccentric training on muscle strength, cross-sectional area, andneural activation. J Appl Physiol 81: 2173–2181, 1996.

21. Hodges, P and Richardson, C. Altered trunk muscle recruitment inpeople with low back pain with upper limb movement at differentspeeds. Arch Phys Med Rehabil 80: 1005–1012, 1999.

22. Isear, JA Jr, Erickson, JC, and Worrell, TW. EMG analysis of lowerextremity muscle recruitment patterns during an unloaded squat.Med Sci Sports Exerc 29: 532–539, 1997.

23. Kernozek, TW, Torry, MR, Van Hoof, H, Cowley, H, and Tanner, S.Gender differences in frontal and sagittal plane biomechanics duringdrop landings. Med Sci Sports Exerc 37: 1003, 2005.

24. Lindbeck, L and Kjellberg, K. Gender differences in lifting technique.Ergonomics 44: 202–214, 2001.

25. McCaw, ST and Melrose, DR. Stance width and bar load effects onleg muscle activity during the parallel squat. Med Sci Sports Exerc31: 428, 1999.

26. McGinty, G, Irrgang, J, and Pezzullo, D. Biomechanical consid-erations for rehabilitation of the knee. Clin Biomech (Bristol, Avon)15: 160–166, 2000.

27. Meyer, B. A comparison of hip and knee extension torques inconventional and split squat exercises. Master’s thesis, Bloomington,IN: Indiana University, 2005.

28. Mills, P, Morrison, S, Lloyd, D, and Barrett, R. Repeatability of3D gait kinematics obtained from an electromagnetic trackingsystem during treadmill locomotion. J Biomech 40: 1504–1511,2007.

29. O’Brien, A and O’Sullivan, L. A biomechanical, physiological andpsychophysical study of the squat, stoop and semi-squat liftingtechniques. In: Proceedings of the Irish Ergonomics Society AnnualConference. O’Sullivan L and Chan, S eds. Ireland, United Kingdom,University of Limerick, 2005. pp 26–31.

30. Panariello, R, Backus, S, and Parker, J. The effect of the squat exerciseon anterior-posterior knee translation in professional footballplayers. Am J Sports Med 22: 768, 1994.

31. Scaglioni-Solano, P, Song, JE, and Salem, GJ. Lower extremitybiomechanics during different squat depths. Med Sci Sports Exerc37: S393, 2005.

32. Secora, CA, Latin, RW, Berg, KE, and Noble, JM. Comparison ofphysical and performance characteristics of NCAA division Ifootball players: 1987 and 2000. J Strength Cond Res 18: 286–291,2004.

33. Sousa, CO, Ferreira, JJA, and Medeiros, A. Electromyographicactivity in squatting at 40, 60 and 90 knee flexion positions. Rev BrasMed Esporte 13: 310–316, 2007.

34. Troubridge, MA. The effect of foot position on quadriceps andhamstrings muscle activity during a parallel squat exercise. Master’sthesis, The University of Western Ontario, London, Ontario,2000.

35. Wallace, DA, Salem, GJ, Salinas, R, and Powers, CM. Patellofemoraljoint kinetics while squatting with and without an external load.J Orthop Sports Phys Ther 32: 141–148, 2002.

36. Wisloff, U, Castagna, C, Helgerud, J, Jones, R, and Hoff, J. Strongcorrelation of maximal squat strength with sprint performance andvertical jump height in elite soccer players. Br J Sports Med 38: 285–288, 2004.

37. Wretenberg, PER, Feng, YI, and Arborelius, U. High-and low-barsquatting techniques during weight-training. Med Sci Sports Exerc28: 218, 1996.

38. Yu, B, McClure, SB, Onate, JA, Guskiewicz, KM, Kirkendall, DT, andGarrett, WE. Age and gender effects on lower extremity kinematicsof youth soccer players in a stop-jump task. Am J Sports Med33: 1356, 2005.

39. Zeller, BL, McCrory, JL, Kibler, WB, and Uhl, TL. Differences inkinematics and electromyographic activity between men andwomen during the single-legged squat. Am J Sports Med 31: 449,2003.



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Quantifying the Movement and the Influence of Load

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