Blood lactate during exercise: Time course of training adaptation in humans

We determined the time course of adaptation in blood lactate concentration ([La]) during constant-load exercise in response to training. Thirteen healthy subjects (11 males, 2 females) exercised on a cycle ergometer for 30 min/day at a work rate calculated to elicit 70% of pre-training V̇O₂max, 6 days/week for 3 weeks. V̇O₂max and blood [La] during constant-load exercise (training work rate) were determined at the end of each week of training. Training increased V̇O₂max 8.5% (from 48.2 ± 1.5 ml·kg^-1·min^-1 pre-training to 52.3 ± 1.4 ml·kg^-1·min^-1 post-training, P < 0.01) and decreased constant-load blood [La] 53% (from 7.8 ± 0.6 mM pre-training to 3.7 ± 0.3 mM post-training, P < 0.01). The training-induced reduction in exercise blood [La] was well fit to an exponential (5.5 e((-t/2.2)) + 2.3, r = 0.99) with a half-time of 10.7 days. However, this was not the case for the time course of V̇O₂max adaptation. The absolute decrease in blood [La] was correlated with the initial blood [La] (r = 0.88, P < 0.01), but changes in V̇O₂max were not significantly correlated with initial blood [La] (r = -0.14) nor with changes in blood [La] (r = -0.02). We conclude that (1) blood [La] response to constant-load exercise decreases rapidly and exponentially with training, with a t( 1/2 ) of 10.7 days, (2) the magnitude of training adaptation is positively related to the initial blood [La], and (3) the time course and extent of the training-induced adaptations of blood [La] and V̇O₂max appear to be independent of one another.