Skeletal muscle energy metabolism and fatigue during intense contraction in man

The rate of skeletal muscle anaerobic A TP resynthesis is rapid when compared with aerobic resynthesis, however a high rate of anaerobic resynthesis can only be maintained for short periods of time. Table 1 shows the rates of A TP resynthesis from phosphocreatine (pCr) and glycolysis during 30s of near maximal isometrie contraction in man. Af ter only 1.3s of contraction the rate of PCr utilisation begins to decline, while the corresponding rate from glycolysis does not peak until af ter 3s of contraction This suggests that the rapid initial utilisation of PCr may buffer the momentary lag in energy provision from glycolysis. There is also a progressive decline in ATP provision from both substrates af ter their initial peaks e.g. !he rates of A TP provision from PCr and glycolysis during the final lOs of contraction amount to 2 and 40%, respectively of their respective peak rates of production. Similar findings, involving isokinetic and dynamic exercise, have been reported by other research groups (Boobis et al. 1982, Jones et al. 1985). Interestingly, in all of these studies, in conjunction with the decline in anaerobic A TP production was a decline in force production and power output. It is tempting to postulate therefore, that the development of fatigue was attributable to the decline in ATP provision. Alternatively however, the decline in energy provision may simply be a function of a decline in the rate of A TP utilisation which will accompany any decline in force production.