Dependence of lactate removal on muscle metabolism in man

Summary If lactate is primarily oxidized in skeletal muscle in man, it is expected that lactate uptake would increase linearly with increasing muscle metabolism (VO₂). Therefore, lactate removal was investigated (N=9) after 6 min exercise bouts (90% VO₂ max), at rest, and during 30 min of recovery exercise, when the relative intensities were constant to equate lactate production while permitting exercise metabolism (VO₂) to vary. Recovery exercises were therefore conducted at 26.8% VO₂ max for arm exercise, 26.8% VO₂ max for leg exercise, and 29% VO₂ max for combined arm and leg exercise. These exercise intensities were calculated from VO₂ max values established separately for each of the three modes of exercise. Lactate removal was slowest at rest (p<0.05). Removal during leg recovery was faster than during the arm condition (p<0.05), but the leg removal was not different from the combined arm and leg condition (p>0.05). The VO₂ cost of the arm (0.73±0.04 l/min), leg (1.04±0.05 l/min) and combined arm and leg exercise (1.23±0.10 l/min) were distinctly different from each other (p<0.05). There was a high correlation (r=0.92) between VO₂ cost, and the lactate removal rates of the corresponding recovery conditions. These findings indicate that lactate increases proportionately with the metabolically active muscle mass, providing exercise remains aerobic. Thus in man, it appears that lactate removal from the blood during recovery exercise occurs primarily in skeletal muscle.