Low values of blood viscosity and erythrocyte aggregation are associated with lower increases in blood lactate during submaximal exercise

Trained sportsmen have low values of blood viscosity (ηb). In this study we tested the functional consequences of this reduction of ηb in 34 sportsmen submitted to a 25 min progressively increasing submaximal work load. A low resting ηb (measured at high shear rate with the MT90 viscometer) was associated to a lower increase in blood lactate during exercise (correlation of ηb with: maximal lactate value: r=0.357 p < 0.05; area under the curve: r=0.490 p < 0.01). Subjects with ηb > 2.4 mPa.s (with this method) had higher lactate increase (p < 0.01) and a deeper decrease in blood bicarbonate (p < 0.001). RBC rigidity (‘Tk’ index) is increased proportionaly to lactate when lactate increases above 4 mmol.l⁻¹. Another group of 21 professional footballers was studied during a maximal triangular work load until VO₂ max. In this group there was a correlation between maximal lactate response during the test and RBC aggregation (r=0.705 p < 0.005). These results suggest that low whole blood viscosity at rest either (a) prevents from excessive lactate increase in this kind of exercise protocol; (b) or is a marker of trained persons characterized by metabolic/circulatory adaptations protecting against exercise-induced hyperlactatemia. In these experimental conditions lower RBC aggregation (within the normal range) seems to be also associated with fitness and lower lactate increase.