Formation of Lactic Acid, an Initial Process in Working Muscle*

The early chemical changes in continuously contracting muscle have been definitely shown to involve anaerobic reactions. The formation of lactic acid from glycogen, the hydrolysis of phosphocreatine, the hydrolysis of adenosinetriphosphate, and the formation of hexosemonophosphate liberate energy which may be used for muscular contraction. Most of the theories of muscular contraction postulate some degree of interdependence of these reactions and an oxidative recovery phase involving the reversal of the anaerobic reactions. With continuous work the oxidativc recovery of these substances is assumed to increase until the resynthesis is equal t,o the somewhat lessened anaerobic hydrolysis when a steady state is reached. The immediate energy of contraction is considered as being continually derived from the anaerobic processes maintained in continuous reaction by energy from oxidative,processes. Lundsgaard (1) in a recent review stated that the question might well be raised as to the extent to which the known anaerobic processes participate in the metabolism of aerobically working muscle; that is, muscle working with unimpaired circulation and adequate oxygen supply. Sacks and his collaborators (2-4), as well as others since Embden et al. (5), have seriously questioned tfhe part played by the anaerobic processes in the contraction of muscle working aerobically and have indicated that the chemical reactions of anaerobiosis are much less definitely related than they were assumed to be. Sacks, Sacks, and Shaw (3) compared the chemical changes occurring during and after stimulation of muscle