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Muscle Adaptation to Exercise

Atrophy: Denervation atrophy

If the neurons to a skeletal muscle are destroyed or the neuromuscular junctions become nonfunctional, the denervated muscle fibers will become progressively smaller in diameter, and the amount of contractile proteins they contain will decrease.

Atrophy: Disuse atrophy

A muscle with its nerve supply intact if the muscle is not used for a long period of time, as when a broken arm or leg is immobilized in a cast.

Hypertrophy

Increased amounts of contractile activity (exercise) can produce an increase in the size of muscle fibers as well as changes in their capacity for ATP production.

Aerobic training (Exercise)

exercise that is of relatively low intensity but of long duration

∞ increases in the number of mitochondria in the fibers

∞ increase in the number of capillaries around these fibers

∞ increase in the capacity for endurance activity with a minimum of fatigue

Strength training (Exercise)

short duration, high-intensity exercise that affects primarily the fast-glycolytic fibers, which are recruited during strong contractions

∞ increase in fiber diameter

∞ increase in the strength of the muscle and the bulging muscles of a conditioned weight lifter

∞ little capacity for endurance

Exercise

produces little change in the types of myosin enzymes formed by the fibers and thus little change in the proportions of fast and slow fibers in a muscle

does change the rates at which metabolic enzymes are synthesized, leading to changes in the proportion of oxidative and glycolytic fibers within a muscle

Effect on the cardiovascular system

Partially prevent the loss of muscle tissue that occurs with aging

Helps maintain stronger bones

Aerobic Training Strength Training

Muscle Soreness

extensive exercise by an individual whose muscles have not been used in performing that particular type of exercise

result of a mild inflammation in the muscle, which occurs whenever tissues are damaged

Lever Action of Muscles and Bones

Flexion and Extension

Flexion - bending of a limb at a joint

Extension- Straightening of a

limb

Antagonists

groups of muscles that produce oppositely directed movements at a joint

Flexion and Extension

Skeletal-Muscle Disease

Muscle Cramps

Produces by involuntary tetanic contraction of skeletal muscles

Nerve action potentials fire at abnormally high rates

Hypocalcemic Tetany

The involuntary tetanic contraction of skeletal muscles that occurs when the extracellular calcium concentration falls to about 40% of its normal value.

Muscular Dystrophy

Frequently encountered genetic diseases, most commonly in boys.

Associated with the progressive degeneration of skeletal- and cardiac-muscle fibers, weakening the muscles and leading ultimately to death from respiratory or cardiac failure.

Myasthenia Gravis

Characterized by muscle fatigue and weakness that progressively worsens as the muscle is used.

Symptoms result from a decrease in the number of ACh receptors on the motor end plate.

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