Muscles at work

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

1. Maximal strength 2. Power 3. Muscular endurance

The greater the fast-twitch fiber 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

The greater the slow-twitch fiber content of a muscle...

1. The lower the force-producing capacity 2. The slower the contraction speed 3. The greater the endurance characteristics of the muscle

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

Relative strength

A clear relationship exists between the proportion of maximal strength and body mass.

Isokinetic contraction

A dynamic contraction Isokinetic (iso = same or constant, kinetic = motion) Involves a constant speed contraction against a preset high resistance Generation of a high level of tension within a muscle at all joint angles

Plyocentric contraction

A hybrid contraction The muscle performs an isotonic concentric contraction from a stretched position Involves a "prestretching" of the muscle to initiate the Golgi tendon organ reflex

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

Age

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

Isotonic 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

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

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

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

Isokinetic contraction: Examples of dynamometers that allow for isokinetic contraction include:

Cybex Kin-Com Lido HydraGym Nautilus

The Relationship Between Maximal Strength and Power

Development of maximal strength through hypertrophy of myofibrils

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

Isotonic 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

The Relationship Between Maximal Strength and Power

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

Isotonic contraction

For example, the strength needed to perform a barbell curl depends on a number of internal factors 1. The athlete's physique 2. The athlete's leverage 3. The angle position of the limbs 4. The speed of the movement

Maximal strength

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

Relative strength

Gymnasts rely heavily upon the development of relative strength

Power

Important for performance in activities that require mastering quick movements Includes sprinting, speed-skating, jumping, throwing, rowing, etc.

The Relationship Between Maximal Strength and Power

Improved intramuscular coordination results in a progressive increase in the number of fast motor units that can be mobilized Therefore, maximal strength training can be beneficial to the development of power

Factors Influencing the Force and Power of Muscle Contractions:

Individual's state of health Individual's training status Joint angle Muscle cross-sectional area Speed of movement Muscle fiber type Age Gender

Eccentric contraction

Involves muscle lengthening during movement; usually termed extension

Concentric contraction

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

Isotonic contraction example

Lowering a load at a slow and constant speed is an example of an isotonic contraction.

Maximal and Absolute Strength

Maximal and absolute strength are important to athletes who are required to overcome the resistance of a partner or equipment

Joint angle

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

Examples of concentric and eccentric contractions

Moving the heel closer to the buttocks is an example of a concentric contraction of the hamstrings. Moving the heel away from the buttocks is an example of an eccentric contraction of the hamstrings.

Dynamic contraction

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

Static contraction

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 In most sports, the need for maximal static contraction is rare Maximal static contraction is seen in gymnastics, wrestling, and judo Most sports require low to submaximal static contraction Examples of sports that require this type of contraction include windsurfing, alpine skiing, and shooting events

Muscular endurance

Muscular endurance is important in acyclic events that involve strength and endurance, including gymnastics, wrestling, boxing, and downhill skiing

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 = Maximal Strength Body Mass

Relative strength

Relative strength can also be gained by increasing strength and stabilizing body mass

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

Issues Related to the Relationship Between Strength and Endurance

Repetitive maximal strength training decreases endurance, but increases strength

Plyocentric contraction

The Golgi tendon organ reflex protects muscles from too much stretch, and causes them to contract Activities that utilize this type of contraction to train jumping ability include leaping and bounding

Power

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

Maximal strength

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

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

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

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

Gender

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

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

One rep max

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

Muscle Cross-sectional Area

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

The Relationship Between Maximal Strength and Power

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)

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

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

Isokinetic contraction

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

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

Relative strength

Young recreational athletes should strive to develop strength in addition to increasing active body mass