Muscular exercise, lactic acid, and the supply and utilisation of oxygen.—Part XIV. The relation in man between the oxygen intake during exercise and the lactic acid content of the muscles

Hartree and A. V. Hill (1) have shown in the isolated frog’s muscle that the maximum rate of the recovery heat-production is proportional to the square of the total initial heat liberated by the stimulus. This relation has been amply confirmed by Hartree, in experiments hitherto unpublished on the isolated muscle of the tortoise. Hartree and Hill concluded that the speed of the recovery oxidation is at any moment proportional to the square of the concentration of the reacting bodies present at that moment, and suggested that a bimolecular reaction of some kind, possibly involving two lactic acid molecules, might be the determining agent in the velocity of the recovery oxidation. Up to the present it has not been shown that any substances other than lactic acid and oxygen are directly concerned in the recovery process in muscle, so the above relationship can be put in terms of these substances. Expressed in a formula, (rate of oxidation) ∝ (rate of lactic acid removal) =k (concentration of lactic acid)2 , wherek is a velocity constant. In a recent paper Meyerhof, Lohmann and Meier (2) have shown that isolated frog’s muscle perfused by, or suspended in, an oxygenated Ringer’s solution containing sodium lactate will cause a diminution in the amount of lactate in the perfusing fluid, with an uptake of oxygen and a synthesis of glycogen. In these experiments it was obvious that the lactate ion was the determining factor in exciting the oxidation by which the energy was supplied to effect the synthesis of the glycogen. Moreover, as Hartree and Hill have shown (3), a rise of hydrogen ion concentration alone does not increase, but rather decreases, the speed of the recovery process in muscle. It seemed obvious, therefore, that the lactate ion itself was to be regarded as the governing factor in the speed of oxidation.