Chapter 4
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 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
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Forms and types of muscle contraction
Static Dynamic
Isometri c
Isotonic Auxotonic Isokinetic Plyocentric
Concentric Eccentric
Concentric
(overcoming, accommodating)
Eccentric
(resistive)
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Forms and types of muscle contraction
Static Dynamic
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Forms and types of muscle contraction
Static
Isometric
Concentric Eccentric
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Forms and types of muscle contraction
Dynamic
Isotonic Auxotonic Isokinetic Plyocentric
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Dynamic
Isotonic Auxotonic Isokinetic Plyocentric
Concentric
(overcoming, accommodating)
Eccentric
(resistive)
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Forms and types of muscle contraction
Static Dynamic
Isometri c
Isotonic Auxotonic Isokinetic Plyocentric
Concentric Eccentric
Concentric
(overcoming, accommodating)
Eccentric
(resistive)
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 Muscle tension or internal force exerted against an external load
 Internal force is equal to, or weaker than, the external load
 No visible movement of the external load occurs
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 In most sports, the need for maximal static contraction is rare
 Maximal static contraction is most often seen in gymnastics, wrestling, and judo
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 Most sports require low to submaximal static contraction
 Examples of sports that require this type of contraction include sail-boarding, alpine skiing, and shooting events
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Activities Requiring
Sub-Maximal Static Muscle Tension
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 Muscle 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
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 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
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Pushing against a stable wall is an example of an isometric contraction
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An isometric contraction occurs during an arm wrestling match when opponents generate equal forces
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 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
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4.
For example, the strength needed to perform a barbell curl depends on a number of internal factors
These factors include:
The athlete’s physique
The athlete’s leverage
The angle position of the limbs
The speed of the movement
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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
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 A dynamic contraction
 A change in muscle length occurs
 Constant tension is achieved and maintained
 Rarely encountered in sports and athletic events because a change in tension is usually required with a change in joint angle
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 Lowering a heavy weight at a slow and constant speed is an example of an isotonic contraction
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 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
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Examples of dynamometers that allow for isokinetic contraction include:
1.
2.
3.
4.
5.
CYBEX
KINCOM
LIDO
HydraGym
Nautilus
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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
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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
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 A hybrid contraction
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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
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The individual’s state of health
The individual’s training status
Joint angle
Muscle cross-sectional area
Speed of movement
Muscle fibre type
Age
Gender
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 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
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Maximal force is produced at a joint angle that corresponds to maximal cross-bridge interaction
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 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
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 The heaviest weights of all are lifted by athletes in the superheavyweight category
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 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
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 Maximal and absolute strength are important to athletes who are required to overcome the resistance of a partner or equipment
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 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
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 Gymnasts rely heavily upon the development of relative strength
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 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
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 Relative strength can also be gained by increasing strength and stabilizing body mass
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 Young recreational athletes should strive to develop strength in addition to increasing active body mass
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 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
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1.
Three main components of strength related to speed of movement are:
Maximal strength
2.
3.
Power
Muscular endurance
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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
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 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
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 Greater absolute strength is necessary for activities such as weightlifting and field events in track & field
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Power:
The ability to overcome external resistance by developing a high rate of muscular contraction; also known as
‘speed-strength’
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Important for performance in activities that require mastering quick movements
Includes sprinting, speed-skating, jumping, throwing, rowing, etc.
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Muscular Endurance:
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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 crosscountry skiing
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Muscular endurance is important in acyclic events that involve strength and endurance, including gymnastics, wrestling, boxing, and downhill skiing
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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
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The Relationship Between Maximal
Strength and Power
 Fast-twitch muscle fibres increase in diameter in response to high-resistance training
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The Relationship Between Maximal
Strength and Power
Development of maximal strength through hypertrophy of myofibrils
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The Relationship Between Maximal
Strength and Power
 Improved intra-muscular coordination results in a progressive increase in the number of fast motor units that can be mobilized
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The Relationship Between Maximal
Strength and Power
Development of maximal strength through increased intra-muscular coordination
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The Relationship Between Maximal
Strength and Power
 Therefore, maximal strength training can be beneficial to the development of power
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The Relationship Between Maximal
Strength and Power
Development of maximal strength through hypertrophy and increased intra-muscular coordination
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The Relationship Between Maximal
Strength and Muscular Endurance
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The number of repetitions that can be performed against a highresistance 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)
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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
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Issues Related to the Relationship
Between Strength and Endurance
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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
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Issues Related to the Relationship
Between Strength and Endurance
Repetitive maximal strength training decreases endurance, but increases strength
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Issues Related to the Relationship
Between Strength and Endurance
 A Nordic event skier competing in ski jumping and cross-country skiing must combine training for maximal strength as well as muscular endurance
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Issues Related to the Relationship
Between Strength and 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
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2.
3.
The greater the fast-twitch fibre content of a muscle…
The greater the force output;
The greater the overall speed of contraction; and
The greater the fatigability will be when the muscle has been maximally activated
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2.
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The greater the slow-twitch fibre content of a muscle…
The lower the force-producing capacity
The slower the contraction speed
The greater the endurance characteristics of the muscle
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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
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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
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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
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 The differences between males and females is mainly due to the difference that exists in muscle volume
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