Arterial blood lactate concentrations were measured on 19 subjects before, during, and after a 3-min bicycle exercise at several work rates, and the concentrations during the recovery phases were fitted to a biexponential time function consisting of a rapidly increasing and a slowly decreasing component. Highly significant correlations with the work rate of the exercise preceding the recovery were found for all the parameters of the fitted equation. The two velocity constants show inverse linear relationships, whereas the other parameters vary according to a definite power function. A functional meaning has been given to the two velocity constants, namely the ability of the tissues to exchange and to remove lactate. For the group of subjects studied, after exercises at work rates below about 3.5 W/kg, the tissue's ability to utilize, and possibly to exchange lactate, increases over values generally reported for resting conditions, whereas after exercises at higher work rates the inverse occurs. Lactate kinetics during recovery appear to be the result of two underlying processes, one enhancing the ability of the tissues to exchange and remove lactate and the other restraining it.

The relationships between individual performance and lactate exchange and removal abilities were studies in 12 male rowers all subjected to three measurements on a rowing ergometer. An incremental exercise carried out to determine the maximal oxygen uptake (VO2max) and the corresponding maximal aerobic power (Pamax), a 2500-m all-out test where the mean work rate (P2500) represented the individual performance, and a 6-min 90% Pamax exercise designed to assess the lactate kinetics during the following 90 min passive recovery were performed. The lactate recovery curves were fitted to the bi-exponential time function: La(t) = La(O) + A1(1-e-gamma 1.t) + A2(1-e-gamma 2.t). The velocity constants gamma 1 and gamma 2 denote the lactate exchange and removal abilities, respectively. The mean value of P2500 sustained by the rowers was 376 +/- 41W (106 +/- 5% of Pamax (P2500%). P2500 was positively correlated with gamma 2 (P < 0.05). gamma 1 and gamma 2 explained 67% of the P2500 variance. P2500% was also correlated with gamma 2 (P < 0.01). These results suggest that a better performance on the rowing ergometer is associated with improved lactate exchange and removal abilities. Furthermore, the ability to row at high relative work rates was correlated with an increased lactate removal ability. Training-induced adaptations could explain the high gamma 1 and gamma 2 displayed by the present rowers.

The purpose of this study was to investigate whether track running specialisation could be associated with differences in the ability to exchange and remove lactate. Thirty-four male high-level runners were divided into two groups according to their specialty (100 - 400 m/800 - 1500 m). All performed a 1-min 25.2 km x h -1 event, followed by a 90-min passive recovery to obtain individual blood lactate recovery curves which were fitted to a bi-exponential time function: [La](t) = [La](0) + A 1 (1-e -gamma1t) + A 2 (1-e -gamma2t). The velocity constant gamma 1 which denotes the ability to exchange lactate between the previously worked muscles and blood was higher (p < 0.001) in middle-distance runners than in sprint runners. The velocity constant gamma 2 which reflects the overall ability to remove lactate did not differ significantly between the two groups. gamma 1 was positively correlated with the best performance over 800 m achieved by 16 athletes during the outdoor track season following the protocol (r = 0.55, p < 0.05). In conclusion, the lactate exchange ability seems to play a role on the athlete's capacity to sustain exercise close to 2-min-duration and specifically to run 800 m.

The effects of 4 weeks of endurance training in conditions of normoxia or hypoxia on muscle characteristics and blood lactate responses after a 5-min constant-load exercise (CLE) at 90% of the power corresponding to the maximal oxygen uptake were examined at sea-level in 13 sedentary subjects. Five subjects trained in normobaric hypoxia (HT group, fraction of oxygen in inspired gas = 13.2%), and eight subjects trained in normoxia at the same relative work rates (NT group). The blood lactate recovery curves from the CLE were fitted to a biexponential time function: La(t) = La(0) + A1(1 - e- gamma 1.t) + A2(1 - e- gamma 2.t), where the velocity constants gamma 1 and gamma 2 denote the lactate exchange and removal abilities, respectively, A1 and A2 are concentration parameters that describe the amplitudes of concentration variations in the space represented by the arterial blood, La(t) is the lactate concentration at time t, and La(0) is the lactate concentration at the beginning of recovery from CLE. Before training, the two groups displayed the same muscle characteristics, blood lactate kinetics after CLE, and gamma 1 and gamma 2 values. Training modified their muscle characteristics, blood lactate kinetics and the parameters of the fits in the same direction, and proportions among the HT and the NT subjects. Endurance training increased significantly the capillary density (by 31%), citrate synthase activity (by 48%) and H isozyme proportion of lactate dehydrogenase (by 24%), and gamma 1 (by 68%) and gamma 2 (by 47%) values. It was concluded that (1) endurance training improves the lactate exchange and removal abilities estimated during recovery from exercises performed at the same relative work rate, and (2) training in normobaric hypoxia results in similar effects on lactate exchange and removal abilities to training in normoxia performed at the same relative work rates. These results, which were obtained non-invasively in vivo in humans during recovery from CLE, are comparable to those obtained in vitro or by invasive methods during exercise and subsequent recovery.