VARIATIONS IN LACTATE APPARENT CLEARANCE DURING REST AND EXERCISE IN NORMAL MAN

The purpose of this study is to present a simple kinetic model for the study of the lactate metabolism. This model based on pharmacokinetic theory, does not require labelled molecules and yields a finer approach to lactate metabolism than does a simple observation of blood lactate concentration. The variations in parameter values have been studied in six male subjects after intensive exercise (385 W, 110 rpm and 1 min) (IE) followed by three different recovery periods : passive recovery (RE), moderate exercise (ME) and heavy exercise (HE). Blood lactate concentration was measured prior to IE and during the first hour of recovery. After mathematical treatment, the results show that the apparent clearance increases 2.83 +/- 0.76 fold from RE to ME and 1.96 +/- 0.61 fold from RE to HE. The steady state blood lactate concentration induced by the intensity of recovery (La(ss)) increases slightly (1.53 +/- 0.37 fold) from RE (1.40 +/- 0.36 mmol.1-1) to ME (2.04 +/- 0.32 mmol.1-1). Then La(ss) increases markedly (3.78 +/- 0.91 mmol.1-1) during HE (2.81 +/- 0.78 fold the La(ss) value at RE). The ratio between the apparent rates of lactate production (F''K0) during RE, ME and HE was calculated. F''K0 increases in a linear way versus intensity of exercise recovery. It was concluded that in the human : 1) the blood lactate concentration is not an accurate indicator of lactate production, 2) in our experiment, the apparent lactate production is a linear function of exercise intensity and 3) the abruptly increasing blood lactate concentration at a high level of exercise intensity is due to a decrease in apparent clearance.