Sport Books Publisher1 Muscles at Work Chapter 4.

Sport Books Publisher 1

Muscles at Work

Chapter 4


Objectives To be able to identify and describe the

different types of muscle contractions To identify the components of strength To gain an understanding of the relationships

among strength components To describe the factors that influence

strength development To evaluate resistive force and power

patterns of exercise devices To analyze sports movements and make

movement-oriented exercise prescriptions


Types of Muscle Contractions


Types of Muscle Contraction

Concentric Eccentric

Isometric

Static

Isotonic Auxotonic Isokinetic Plyocentric

Concentric(overcoming, accommodating)

Eccentric(resistive)

Forms and types of muscle contraction

Dynamic



Static Dynamic





Isometric

Static




Dynamic






Concentric(overcoming,accommodating)

Eccentric(resistive)

Dynamic




Isometric

Static


Concentric(overcoming, accommodating)

Eccentric

(resistive)


Dynamic


Static ContractionMuscle tension or internal force

exerted against an external load Internal force is equal to, or

weaker than, the external loadNo visible movement of the

external load occurs


Static ContractionIn most sports, the need for

maximal static contraction is rare

Maximal static contraction is most often seen in gymnastics, wrestling, and judo


Activities Requiring Maximal Static Muscle Tension


Static ContractionMost sports require low to sub-

maximal static contractionExamples of sports that require

this type of contraction include sail-boarding, alpine skiing, and shooting events


Activities Requiring Sub-Maximal Static Muscle Tension


Dynamic ContractionMuscle tension or

force is exerted against an external load

Internal force exerted is greater than the external load

Visible movement of the external load occurs


Isometric Contraction A static contraction Muscle contraction against an external

force No visible change in muscle length External load is greater than the force

generated by the internal force No external movement occurs No work is performed because no

movement occurs A high amount of tension is developed,

energy is used


Pushing against a stable wall is an example of an isometric contraction


An isometric contraction occurs during an arm wrestling match when opponents generate equal forces


Auxotonic Contraction A dynamic contraction During dynamic work, continual

changes in joint angle and speed result in changes in strength needs

That is, the tension required to move an external load varies

The involvement of more or less motor units allows the muscle to adapt to changing tension requirements


Auxotonic Contraction For example, the strength

needed to perform a barbell curl depends on a number of internal factors

These factors include:1. The athlete’s physique2. The athlete’s leverage3. The angle position of the

limbs4. The speed of the movement


Auxotonic Contraction Although the weight of the barbell remains

the same, these factors may compromise an athlete’s capacity for strength gains at all joint angles

Therefore, it is not easy to gain equal strength gains at all joint angles when training with free-weights alone


Isotonic ContractionA dynamic contractionA change in muscle length occurs Constant tension is achieved and

maintainedRarely encountered in sports and

athletic events because a change in tension is usually required with a change in joint angle


Isotonic Contraction

Lowering a heavy weight at a slow and constant speed is an example of an isotonic contraction


Isokinetic Contraction A dynamic contraction Involves a constant speed contraction

against a preset high resistance Generation of a high level of tension within a

muscle at all joint angles Thus, muscle strengthening also occurs at

all joint angles With the use of certain machines, constant

tension can be achieved as joint angle and movement velocity are controlled


Isokinetic Contraction Examples of dynamometers that

allow for isokinetic contraction include:

1. CYBEX2. KINCOM3. LIDO4. HydraGym5. Nautilus


Concentric and Eccentric Contractions

Concentric Contraction:

Involves muscle shortening as it goes through a range of motion; usually termed flexion

Eccentric Contraction:

Involves muscle lengthening during movement; usually termed extension


Examples of Concentric & Eccentric Contractions

Moving the heel closer to the buttocks is an example of a concentric contraction of the hamstring

Moving the heel away from the buttocks is an

example of an eccentric contraction of the

hamstring


Plyocentric Contraction A hybrid contraction The muscle performs an isotonic concentric

contraction from a stretched position Involves a “pre-stretching” of the muscle to

initiate the Golgi tendon organ reflex The reflex causes the muscles to contract Plyocentric training can result in functional

strength gains beyond those that can be achieved through strength training alone


Plyocentric Training


Factors Influencing Muscle Contraction


Factors Influencing the Force and Power of Muscle Contractions:1. The individual’s state of health

2. The individual’s training status

3. Joint angle

4. Muscle cross-sectional area

5. Speed of movement

6. Muscle fibre type

7. Age

8. Gender


Joint Angle The type of contraction and the force required

to resist an external load change as the joint angle changes

The contraction type and force required depend on whether the external force exceeds, or is less than, the internal (applied) force

Static, dynamic, concentric, and eccentric contractions may all be required

Coordination between agonist and antagonist muscles is required


Joint Angle

Maximal force is produced at a joint angle that corresponds to maximal cross-bridge interaction


Muscle Cross-Sectional Area Body mass is positively correlated with

strength, provided that the mass is primarily muscle tissue or lean mass

The larger the muscle cross-sectional area, the more force it can generate


Muscle Cross-Sectional Area


Muscle Cross-Sectional Area

The heaviest weights of all are lifted by athletes in the super-heavyweight category


Maximal and Absolute Strength The greater the active body mass, the greater

the maximal or absolute strength However, individuals of a smaller and lighter

physique may possess a relatively high strength potential when the following factors are considered:

• Intramuscular coordination• Intermuscular coordination• Anatomical structure• Muscle elasticity


Maximal and Absolute Strength Maximal and absolute strength are

important to athletes who are required to overcome the resistance of a partner or equipment


Relative Strength The performance of athletes classified

by weight, or athletes who must overcome their own body mass, depends on the proportion of maximal strength to body mass

Relative Strength = Maximal Strength Body Mass


Relative Strength

Gymnasts rely heavily upon the development of relative strength


Relative Strength Recreational athletes are usually

interested in increasing active strength and reducing body mass

This method is also used by overweight athletes who want to lose fat mass


Relative Strength Relative strength can also be gained

by increasing strength and stabilizing body mass


Relative Strength Young recreational athletes should strive

to develop strength in addition to increasing active body mass


Speed of Movement

As speed of movement increases, the force a muscle can generate decreases

Cross bridges are compromised since they cannot couple and uncouple fast enough

Thus, there is a decreased ability to establish and maintain a large number of cross bridges


Speed of Movement

Three main components of strength related to speed of movement are:

1. Maximal strength

2. Power

3. Muscular endurance


Maximal Strength

Maximal Strength:

The ability to perform maximal voluntary muscular contractions in order to overcome powerful external resistances

One Repetition Maximum (1RM):

The greatest force that can be exerted during one repetition for a given contraction of muscles


From Greek Mythology… The alertness and

great strength of Hercules, the hero of Greek mythology, allowed him to perform extraordinary deeds

The name Hercules suggests a human being of giant stature and great physical strength


Maximal Strength

Greater absolute strength is necessary for activities such as weightlifting and field events in track & field


Power

Power:

The ability to overcome external resistance by developing a high rate of muscular contraction; also known as ‘speed-strength’


Power Important for

performance in activities that require mastering quick movements

Includes sprinting, speed-skating, jumping, throwing, rowing, etc.


Muscular Endurance

Muscular Endurance:

The ability to resist fatigue in strength performance of longer duration; also known as ‘strength endurance’

Muscular endurance determines performance capacity in events that occur over longer periods of time, such as rowing, swimming, and cross-country skiing


Muscular Endurance Muscular endurance is important in acyclic

events that involve strength and endurance, including gymnastics, wrestling, boxing, and downhill skiing


The Relationship Between Maximal Strength and Power

Common misconception that increases in maximal strength lead to slowed muscle performance

In fact,• The more internal force that can be

generated to overcome external resistance, the more movement acceleration increases

• The higher the external resistance to be overcome, the more important the maximal strength for power performance



Fast-twitch muscle fibres increase in diameter in response to high-resistance training



Development of maximal strength through hypertrophy of myofibrils



Improved intra-muscular coordination results in a progressive increase in the number of fast motor units that can be mobilized



Development of maximal strength through increased intra-muscular coordination



Therefore, maximal strength training can be beneficial to the development of power



Development of maximal strength through hypertrophy and increased intra-muscular coordination


The Relationship Between Maximal Strength and Muscular Endurance

The number of repetitions that can be performed against a high-resistance is dependent on maximal strength

That is, the greater an athlete’s maximal strength, the greater the muscular endurance at a particular load (as a percentage of 1RM)


The Relationship Between Maximal Strength and Muscular Endurance

Resistance Level 100% 95% 90% 85% 80% 75%

Repetition Maximum 1 2-3 5-6 7-8 10-12 12-16


Issues Related to the Relationship Between Strength and Endurance

Vigorous cardiovascular training can lead to an associated decrease in the diameter of fast-twitch muscle fibres

Thus, increased endurance can be associated with decreased muscle strength as a result of a corresponding decrease in muscle volume



Repetitive maximal strength training decreases endurance, but increases strength



A Nordic event skier competing in ski jumping and cross-country skiing must combine training for maximal strength as well as muscular endurance



Relatively high levels of both strength and endurance can be achieved either by training for strength and endurance in separate training sessions, or in combination


Muscle Fibre Type The greater the fast-twitch fibre

content of a muscle…

1. The greater the force output;

2. The greater the overall speed of contraction; and

3. The greater the fatigability will be

when the muscle has been maximally activated


Muscle Fibre Type The greater the slow-twitch fibre

content of a muscle…1. The lower the force-producing

capacity2. The slower the contraction speed3. The greater the endurance

characteristics of the muscle


Age Aging affects muscle force output There is a loss of fast-twitch fibres

associated with aging May occur as a result of apoptosis May occur as a result of disuse ‘Sarcopenia’ is the medical term that

describes muscle loss


Age Diminished strength and balance is

associated with muscle loss This may lead to falls and bone fractures Falls and fractures are a major cause of

age-related disabilities


Gender

The absolute force and power capacity of women is often less than that of men

However, there is not much difference between males and females when force and power data are normalized to selected anatomical variables


Gender

The differences between males and females is mainly due to the difference that exists in muscle volume

Sport Books Publisher1 Muscles at Work Chapter 4.

Documents

Transcript of Sport Books Publisher1 Muscles at Work Chapter 4.