Kinetics and mechanism of oxygen debt contraction in man

Oxygen consumption, along with lactic and pyruvic acid in blood, have been measured throughout the performance of heavy muscular exercise of different intensities, all leading to exhaustion in 1–10 min. Oxygen consumption increases exponentially with time; the maximum level attained seems to be independent of the intensity of exercise except in exercises of very high intensity and short duration, when it seems to be slightly increased. The rate of increase of oxygen consumption increases with the intensity of exercise. Pyruvic acid in blood increases exponentially also, and a steady state is reached at a level which tends to be higher, the heavier the exercise. Lactic acid increases as a linear function of time, the line eventually flattening down only toward the end of the exercise when the maximal values of lactic acid are reached. The lactic acid increase, grams per minute, is a linear function of the intensity of exercise; no lactic acid is produced if the exercise is below 220 cal/kg min, or a higher value for athletes. The caloric equivalent of lactic acid production from glycogen can be calculated at about 222 cal/g. This value in man is discussed in relation to previous values given. The kinetic of the lactic acid increase during exercise is in agreement with the hypothesis of an additional (alactacid) mechanism of oxygen debt contraction. Submitted on July 31, 1962