The Recovery Process after Exercise in the Mammal

The Hill-Meyerhof theory of the recovery process occurring in the muscles after exercise postulates that four-fifths of the lactic acid formed is reconverted into muscle glycogen, while the remainder is oxidized. Since Meyerhof has shown that this cycle occurs in the isolated frog muscle, then the muscles themselves must be able to effect this transformation. The exact pathway by which lactic acid is converted into glycogen is not definitely known. In mammalian skeletal muscle the evidence is by no means so clear that the muscles themselves can transform lactic acid into glycogen without the intervention of the liver. Elias and Schubert (1) and Janssen and Jost (2) have demonstrated that while injected lactates are rapidly removed from the blood, there is no immediate deposition of muscle glycogen and no increase in oxygen consumption by the muscles. The resynthesis of muscle glycogen after exercise in the fasting mammal has been studied in a few instances only. Long (3) found in cats under amytal anesthesia that 3 hours after exercise there was little or no restoration of muscle glycogen, but in nonanesthetized animals glycogen deposition occurred more rapidly. McKay (4) found in decapitate preparations that the glycogen content of exercised muscles did not increase after 3 hours recovery. Hinsey and Davenport (5) state that they have confirmed Long’s findings on animals under amytal anesthesia. The mammalian liver can transform d-lactates fed by mouth into liver glycogen with great ease. This has been demonstrated