Plasma, red cell and whole blood lactate concentrations during prolonged treadmill exercise at Vla4

Abstract

The purposes of this study were to test whether a relatively steady state with respect to the blood lactate pool can prevail during a prolonged exercise test (PET) at Vla4, to study the kinetics of the flux of lactate between plasma and cells in relation to lactate concentration [LA] and haematocrit and to test the interrelationships between plasma [PLA], whole blood [BLA] and erythrocyte lactate [ELA]. The study used 7 Standardbred trotters. In the PET they ran at their respective pre‐established Vla4 for 12 min. Before, every 2 min during and 0, 2, 5, 10 and 15 min after exercise, [PLA] and [BLA] as well as packed cell volume (PCV) were determined. [ELA] was calculated from [PLA], [BLA] and PCV. Heart rate was monitored continuously and remained at a relatively steady state of approximately 200 beats/min throughout the PET. Lactate concentrations increased exponentially during PET, [PLA] more rapidly than [BLA] and [ELA]. The diverging curves during exercise and converging declining curves after exercise suggested a delay in attainment of an equilibrium between plasma and cells. The close relationship between [PLA] and [BLA] (r = 0.98) allows derivations from regression equations. As the [LA] accumulation over time is exponential, it is likely that the increase during the first 2 min at any speed up to that causing a [BLA] of 4 mmol/l is marginal and insignificant and a submaximal incremental exercise test using 2 min step intervals could still be used for determination of Vla4. © 1995 EVJ Ltd