THE POSSIBLE MECHANISMS OF CONTRACTING AND PAYING THE OXYGEN DEBT AND THE ROLE OF LACTIC ACID IN MUSCULAR CONTRACTION l

Although direct evidence of a quantitative relationship between oxygen debt and lactic acid production in man has never been given, there is general agreement with A. V. Hill’s hypothesis that the oxygen debt is due to the delayed oxidation of a fraction of the lactic acid produced during the anaerobi .c processes of muscular activity. After the “revolution” produced in muscle physiology by the discoveries of the last few years, m ainiy after Lundsgaard’s work, and the further observations on men, it seemed to us that the lactic acid mechanism alone is inadequate to explain all the processes which occur in the payment of the oxygen debt, particularly for the following reasons: a. It has been observed in isolated muscle that most of the lactic acid is produced after the contraction is over, during the first minute of recovery; this does not seem to agree with the fact that the payment of the oxygen debt at the beginning shows no lag even if the exercise is of very short duration. b. In moderate exercise of long duration in man, involving an oxygen debt of 3 to 4 liters, the changes in lactic acid concentration or in pH of blood are negligible in comparison with the values implied by the assumption of an increment of lactic acid in the body corresponding to the amount of oxygen debt. (See, for the lactic acid concentration in blood following muscular exercise, Owles, 1930; Dill, Edwards, Foiling, Oberg, Pappenheimer and Talbott, 1931; for data on pH, Margaria and Talenti, 1933.) c. There exist oxidative recovery processes following muscular contraction other than the glycogen resynthesis from lactic acid ; Lundsgaard (1931) has demonstrated in muscles poisoned with iodoacetic acid the partial resynthesis of the phosphocreatine in the presence of oxygen and in the absence of any lactic acid formation or remo val; Clark, Eggleton and