Effect of exercise duration on lactate kinetics after short muscular exercise.

Arterial blood lactate concentrations were measured in six normal males before, during and after 3- and 6-min bicycle exercises performed at three different work rates. The lactate recovery curves were fitted to a bi-exponential time function consisting of a rapidly increasing and a slowly decreasing component, which supplied an accurate representation of the changes in lactate concentration. Variations in the parameters of this mathematical model have been studied as a function of the duration of exercise and of the work rate, showing a clear dependence on exercise duration such that increasing exercise length decreases the velocity constants of the fitted curves. In terms of the functional meaning which can be given to these constants, this result indicates that extending exercise duration from 3 to 6 min reduces the ability of the whole body to exchange and remove lactate. This effect did not qualitatively modify the one already described, which is due to increased work rates, but it shifted the ability to exchange and remove lactate towards lower values. The main conclusion of the study is that lactate kinetic data vary as a function of time during exercise. This inference must be accounted for in the interpretation of lactate data obtained during muscular exercise.