Blood lactate accumulation in intermittent supramaximal exercise

Summary

Blood lactate accumulation rate and oxygen consumption have been studied in six trained male runners, aged 20 to 30 years. Subjects ran on a treadmill at a rate representing 172±5%$\dot V_{{\text{O}}_{{\text{2 max}}} }$ for four 45 s sessions, separated by 9 min rest periods. Oxygen consumption was measured throughout. Blood lactate was determined in samples taken from the ear and$\dot V_{{\text{O}}_{\text{2}} }$ was measured at the end of each exercise session, and two, five and nine minutes later. After the fourth exercise session, the same measurements were made every five min for 30 min. 4 subjects repeated a single exercise of the same type, duration and intensity and the same measurements were taken. With repetitive intermittent exercise, gradual increases in blood lactate concentration ([LA]b) occurred, whereas its rate of accumulation (Δ[LA]b) decreased. The amount of oxygen consumed during each 45 s exercise session remained unchanged for a given subject. After cessation of intermittent exercise, the half-time of blood lactate was 26 min, whereas it was only 15 min after a single exercise session.$\dot V_{{\text{O}}_{\text{2}} }$ values, on the other hand, returned to normal after 15 to 20 min. All other conditions being equal, the gradual decrease in Δ[LA]b during intermittent exercise could be explained if the lactate produced during the first exercise session is used during the second period, and/or if the diffusion space of lactate increases. The diffusion space seems to be multicompartmental on the basis of half-time values noted for [LA]b after intermittent exercise, compared with those noted after a single exercise session. The distinction between the rapid return to normal$\dot V_{{\text{O}}_{\text{2}} }$ values and the more gradual return to normal blood lactate levels confirms that there is no simple and direct relationship between oxygen debt and the accumulation of blood lactate after muscular exercise. In practical terms, these results show that the calorific equivalent of lactic acid defined by Margaria et al. (1963) cannot be used in the case of intermittent exercise of supramaximal intensity.