EFFECTS OF TRAINING ON LACTATE PRODUCTION AND REMOVAL DURING PROGRESSIVE EXERCISE IN HUMANS

To determine whether the reduced blood lactate concentrations [La] during submaximal exercise in humans after endurance training result from a decreased rate of lactate appearance (Ra) or an increased rate of lactate metabolic clearance (MCR), interrelationships among blood [La], lactate Ra, and lactate MCR were investigated in eight untrained men during progressive exercise before and after a 9-wk endurance training program. Radioisotope dilution measurements of L-[U-C-14]lactate revealed that the slower rise in blood [La] with increasing O2 uptake (VO2) after training was due to a reduced lactate Ra at the lower work rates [VO2 < 2.27 l/min, < 60% maximum VO2 (VO2max); P < 0.01]. At power outputs closer to maximum, peak lactate Ra values before (215 +/- 28-mu-mol.min-1.kg-1) and after training (244 +/- 12-mu-mol.min-1.kg-1) became similar. In contrast, submaximal (< 75% VO2max) and peak lactate MCR values were higher after than before training (40 +/- 3 vs. 31 +/- 4 ml.min-1.kg-1, P < 0.05). Thus the lower blood [La] values during exercise after training in this study were caused by a diminished lactate Ra at low absolute and relative work rates and an elevated MCR at higher absolute and all relative work rates during exercise.