A linear relationship between ATP degradation and fatigue during high-intensity dynamic exercise in rat skeletal muscle.

The relationship between changes in work output (fatigue) and metabolite concentrations was measured in rat skeletal muscle during the course of dynamic exercise (10 s). After 4 s, work output decreased rapidly to approximately 30% at 8 s. In contrast to the changes in phosphocreatine and lactate, the change in ATP concentration paralleled the reduction in work output. A strong linear relationship (r = 0.95) was found between the relative decrease in ATP and the extent of fatigue. Possible mechanisms underlying this relationship are discussed.