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-14C]lactate revealed that the slower rise in blood [La] with increasing O2 uptake (V̇O2) after training was due to a reduced Lactate Ra at the lower work rates [V̇O2 <2.27 l/min, <60% maximum V̇O2 (V̇O(2 max)); P < 0.01]. At power outputs closer to maximum, peak lactate Ra values before (215 ± 28 μmol·min-1·kg-1) and after training (244 ± 12 μmol·min-1·kg-1) became similar. In contrast, submaximal (<75% V̇O(2 max)) 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.