Abstract

This chapter has examined directly obtained information regarding the ability of human skeletal muscle to provide ATP anaerobically during short-term, high-intensity exercise. Evidence suggests that both PCr and glycolysis are activated instantaneously with the onset of maximal activity. Maximal rates of directly measured anaerobic ATP provision from PCr degradation and glycolysis during intense muscular activity are each ca. 9-10 mmol ATP/kg dm/s. During high-intensity exercise the two sources combine to provide 10-14 mmol ATP/kg dm/s. The capacity of muscle to provide anaerobic ATP is ca. 370 mmol/kg dm during dynamic exercise lasting ca. 3 min. Anaerobic glycolysis provided ca. 80%, and PCr degradation contributed ca. 16% of the total. When the blood flow to the contracting muscle is occluded, the anaerobic ATP capacity decreases to ca. 310 mmol/ kg dm. This reduction is due to a lower glycolytic capacity associated with an inability to remove lactate from the muscles. The only study that compared direct and indirect estimates of the anaerobic capacity suggests that O2 deficit measured at the mouth is a good predictor of the anaerobic capacity of a single muscle group of man, and that O2 debt is a poor predictor. Therefore, estimating anaerobic capacity from the maximally accumulated O2 deficit during whole-body exercise deserves further study. Measurements in skeletal human muscle fiber types indicate that [ATP] is similar in type I and II fibers, whereas type II fibers have [PCr] that are 5-15% higher and [glycogen] that are 10-25% higher than type I fibers. Muscle PCr degradation and glycogenolysis are higher in type II fibers during high-intensity exercise, and PCr resynthesis is faster in type I fibers following exercise. Repeated bouts of exhaustive high-intensity exercise decrease the ability to reactivate the glycogenolytic pathways, thereby reducing the glycolytic anaerobic ATP provision while anaerobic PCr and aerobic energy contributions are maintained. The inability to reactivate glycogenolysis is maintained after muscle H+, lactate, and K+ are returned to resting levels. It is surprising that sprint training does little to increase the resting PCr content and only produces 10-20% increases in glycolytic ATP provision and 6-16% increases in total anaerobic ATP provision. Verf.-Referat (gekuerzt)