THE "RECOVERY OXIDATION" FOLLOWING MUSCULAR EXERCISE

Theories of muscular contraction and related phenomena have undergone profound revision in recent years. The long supported conception of the analogy between the work of a muscle and that of a heat engine has been abandoned in favor of the hypothesis that the contractile tissues function essentially as a sort of chemical engine. It has long been known that acids, specifically carbonic and lactic acids, are by-products or concomitants of muscular work. The studies of A. V. Hill and of Meyerhof have served to promote an explanation of the attendant chemical transformations that has attained widespread vogue. It maintains that during muscular contraction there is a breaking down of glycogen into lactic acid, with liberation of energy. This chemical change is not a direct one; probably the carbohydrate is first resolved into a compound with phosphoric acid, a hexose phosphate, which is the direct precursor of the lactic acid. The