Blood lactate exchange and removal abilities after relative high-intensityexercise: effects of training in normoxia and hypoxia

The effects of 4 weeks of endurance training in conditions of normoxia or h ypoxia on muscle characteristics and blood lactate responses after a 5-min constant-load exercise (CLE) at 90% of the power corresponding to the maxim al oxygen uptake were examined at sea-level in 13 sedentary subjects. Five subjects trained in normobaric hypoxia (HT group, fraction of oxygen in ins pired gas = 13.2%), and eight subjects trained in normoxia at the same rela tive work rates (NT group). The blood lactate recovery curves from the CLE were fitted to a biexponential time function: La((t)) = La((0)) + A(1)(1 - e(-)gamma (1 .t)) + A(2)(1 - e(-)gamma (2 .t)), where the velocity constant s gamma (1) and gamma (2) denote the lactate exchange and removal abilities , respectively, A(1)and A(2) are concentration parameters that describe the amplitudes of concentration variations in the space represented by the art erial 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 tr aining, the two groups displayed the same muscle characteristics, blood lac tate kinetics after CLE, and gamma (1) and gamma (2) values. Training modif ied 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 l actate 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 pe rformed at the same relative work rate, and (2) training in normobaric hypo xia results in similar effects on lactate exchange and removal abilities to training in normoxia performed at the same relative work rates. These resu lts, which were obtained non-invasively in vivo in humans during recovery f rom CLE, are comparable to those obtained in vitro or by invasive methods d uring exercise and subsequent recovery.