Introduction: 

Several studies described lactate distribution in blood under resting conditions and the effects of exercise on plasma and RBC lactate concentrations. Most of the studies used incremental step test or steady state exercise but these exercise protocols do not allow the consideration of influx rates. These investigations did not focus on maximal lactate transport rates across the RBC membrane. The purpose of the present study was to look for the maximal lactate influx rate of erythrocytes (RBC) under physiological conditions. The effects of maximal cycling exercise on lactate distribution between plasma and RBC during recovery with a closed meshed blood sampling were investigated.

Methods: 

Twelve elite cyclists performed a 30 s lasting maximal sprint test on a cycle ergometer adjusted to an isokinetic mode. Blood samples were taken before exercise, directly after and in minute-intervals during recovery to determine lactate concentrations [La] in whole blood, plasma and RBC.

Results: 

The congestion of lactate per time unit in plasma exceeded the lactate influx capacity of RBC causing a significant decrease in the RBC-to-plasma lactate concentration ratio (RBC [La]/Plasma [La]) from 0.54 0.04 before exercise to 0.32 0.03 directly after exercise. Afterwards [La] ratio started to increase again. The maximal lactate influx rate of RBC was 1.64 0.45 mmol*L-1 in 30 s. If we assume a linear development of RBC [La] in the first minute we get an increase of 3.28 0.45 mmol*L-1*min-1.

Discussion: To obtain reliable influx rates, it is important to measure the real initial fluxes (due to equilibration in different compartments). In order to bring transport processes to its limit and to measure initial fluxes, we chose a 30 s maximal cycling test to induce a maximal and fastest increase/congestion in plasma lactate concentration. The decrease in ratio is the consequence of a delayed and limited lactate transport across the RBC membrane. The influx rate of RBC is dependent on the plasma-to-RBC lactate concentration gradient, the RBC/plasma lactate concentration ratio and the permeability of the membrane (density of lactate transporters). But it should be taken into consideration that the total driving force for the co-transport is composed of both the lactate and the proton gradients Especially in competitive sports with maximal effort and short duration lactate/H⁺ flux rates of different tissues might set a limit for performance. Thus the knowledge about lactate flux rates during and after exercise is essential.