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The speed of lactic acid formation in blood has been measured in man as a function of the intensity of exercise and was found to reach a maximum of about 36 mg lactic acid/liter blood per sec, corresponding to about 21.5 kcal (kg hr) or 0.034 hp/kg. The maximal energy release sustained by the alactacid mechanism is of the order of 45 kcal/(kg hr), or 0.07 hp/kg. The alactacid debt, as measured in man running on a treadmill, seems to be approximately proportional to the energy expenditure: it amounts at most to 0.1 kcal/kg or about 1.4 liters O 2 for a man weighing 70 kg. The lactacid debt amounts at most to 0.22 kcal/kg or about 3 liters O 2 for man, on the average. The alactacid oxygen debt contraction is a faster process and it requires 10–30 sec for completion, while the lactacid debt process is completed in about 40 sec in the most strenous exercise. Therefore, at the highest workloads, the only energy source available after 40 sec resides in oxidative processes. oxygen debt; lactic acid Submitted on July 5, 1963
Margaria et al. (Wed,) studied this question.