The effect of training on lactic acid excretion.

Abstract

To determine the effect of training on the lactic acid excreted in the urine after exercise, an untrained subject began regular exercise twice a week for two weeks, and then daily for three weeks. The exercise consisted in carrying a 30 pound load on a treadmill with 7 inch steps for 5 minutes at a rate of between 80 and 85 steps per minute. Samples of urine were collected immediately before, and for approximately half an hour after exercise. The rate of lactic acid excretion before exercise was determined, and the subsequent excess above this resting rate was attributed to the exercise. The results of these determinations at various periods during the experiment are given in the accompanying table. It shows a definite decrease in the excess of lactic acid as the experiment proceeded. Subjectively this decrease was accompanied by somewhat less distress during exercise and by less fatigue afterward. This decrease might be explained by assuming an increased mechanical efficiency, so that less lactic acid was formed by muscular contraction; or the decrease might be due to a better oxidative removal of lactic acid because of changes occurring in the muscle itself, or an increased oxygen supply to the muscles from an improved circulation.