The maximum lactate clearance: a new concept to approach the endurance level of an athlete.

The purpose of this study is to present a mathematical model based on physiological observations which describes the evolution of the blood lactate concentration ([LA-]) versus the oxygen uptake (VO2) during a continuous graded exercise test. This model is based on several assumptions: 1) [LA-] reflects the balance between the rates of appearance and disappearance of the lactate in the blood compartment; 2) VO2 measured at the end of each step, is a linear function of the power output and thus of the time; 3) the appearance rate of lactate into the blood is an exponential function of VO2; 4) the rate of disappearance is a saturable process which can be modelized by Michaelis-Menten kinetics; 5) the volume of distribution of lactate in the blood compartment is a constant during exercise. The parameters used in this model correspond to the integration of several biochemical and physiological phenomenons. The originality of this approach is to express the rate of lactate appearance and disappearance versus VO2 rather than time. Whatever the general pattern of the data, the fitted curve gives always very good results. Especially, the theoretical curve fits the decrease in [LA-] usually observed during the first steps of such an exercise. From the computed parameters the evolution of lactate clearance during a continuous graded exercise test may be modelized. A strong relationship exists between the level of endurance training and the maximum lactate clearance (Clmax) reached during the exercise test. The VO2 for Clmax is an indicator of the shift of the relationship [LA-]-VO2. Then, we propose to use the maximum lactate clearance which is individually determined, to characterize the endurance level of an athlete.