Athletic fatigue is the inability to maintain the required power output for continuing muscular work at a given intensity. Fatigue has an extremely complex physiologic process. Current understanding of athletic fatigue involves the energy system of the muscles and central nervous system.
Fatigue may result from depletion of glycogen and phosphocreatine in muscles, which reduces ATP production. In short-duration exercise, such as sprinting, the fatigue is caused by increased concentration of H+ from accumulated lactic acid, which impairs muscle contraction and ATP production. The central nervous system plays a role in most types of fatigue. Some fatigue results from a failure of neural transmission at a neuromuscular junction, in which the transmission of nerve impulses to the muscle fiber membrane is prevented as a result of reduced synthesis of acetylcholine. The function of enzymes at a neuromuscular junction, such as cho-linesterase, can fail because of low concentration or hypoactivity. Abnormal metabolism of intracel-lular calcium or potassium also can occur, inhibiting muscle relaxation. Perhaps the central nervous system limits exercise performance as a protective mechanism. Perceived fatigue usually precedes physiologic fatigue. Muscular and neural fatigue can be effectively reversed if a combination of procedures is used, including rest, nutrition therapy, and needling therapy for the fatigued muscles. If muscle fatigue is not properly treated, affected individuals have a higher risk of injury.
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