Quick questions on Fatigue mechanisms: WACE Physical Education Studies Unit 3

In all out efforts of a few seconds, the limiting factor is the depletion of phosphocreatine, the fuel of the ATP-PC system. Once phosphocreatine stores fall, the very fast resupply of ATP cannot be maintained and power drops. There is no significant lactate involved here; the fatigue is about running low on the immediate energy store, which is why a series of maximal sprints needs adequate rest to restore phosphocreatine.

In efforts from about ten seconds to two minutes, the anaerobic glycolytic system dominates and produces lactic acid, which dissociates into lactate and hydrogen ions. The accumulation of hydrogen ions raises the acidity in the muscle. This increased acidity interferes with the enzymes of glycolysis and with the contraction process, reducing the muscle's ability to produce force. This is the burning sensation and sudden power loss in events like a 400 metre sprint.

In prolonged submaximal exercise the aerobic system dominates and the causes of fatigue change. Glycogen depletion is central: as muscle and liver carbohydrate stores run low, the athlete cannot sustain the pace and must slow or rely more on fat, which supplies energy more slowly. Dehydration reduces blood volume and impairs the delivery of oxygen and the removal of heat. Rising core body temperature (hyperthermia) further stresses the body and impairs performance.