Question

The cause of skeletal muscle fatigue during extended submaximal exercise is primarily a(n)

A) depletion of glycogen stores.
B) depletion of creatine stores.
C) increased inorganic phosphate (Pi) concentration.
D) depletion of K+ stores.

Answer 1

Muscle fatigue during extended submaximal exercise is primarily caused by depletion of ATP reserves, lactic acid buildup, imbalances in Na+ and K+ levels, and damage to the SR and sarcolemma.

Step-by-step explanation:

Muscle fatigue occurs when a muscle can no longer contract in response to signals from the nervous system. The exact causes of muscle fatigue are not fully known, although certain factors have been correlated with the decreased muscle contraction that occurs during fatigue. ATP is needed for normal muscle contraction, and as ATP reserves are reduced, muscle function may decline. This may be more of a factor in brief, intense muscle output rather than sustained, lower intensity efforts. Lactic acid buildup may lower intracellular pH, affecting enzyme and protein activity. Imbalances in Na+ and K+ levels as a result of membrane depolarization may disrupt Ca2+ flow out of the SR. Long periods of sustained exercise may damage the SR and the sarcolemma, resulting in impaired Ca2+ regulation.