Maximal oxygen uptake and lactate thresholds during exercise are related to blood viscosity and erythrocyte aggregation in professional football players

Correlations among values at rest of blood viscosity (MT 90, high shear rate), RBC Aggregation (Myrenne) and four markers of fitness were investigated in 21 professional football players during a triangular maximal exercise test. Maximal O₂ uptake ( $\dot{\mathrm{V}}$ O₂ max, directly measured) was correlated with resting plasma viscosity (r=−0.666 p<0.01) and blood viscosity at corrected hematocrit 45% (r=−0.426 p<0.05). The physical working capacity $\dot{\mathrm{W}}$ 170 was correlated with $\dot{\mathrm{V}}$ O_2max (r=0.645 p<0.01) and with both resting plasma viscosity (r=−0.524 p<0.02) and hematocrit (r=−0.524 p<0.05). Two determinants of the 4 mmol lactate threshold were found: red cell aggregation ‘M’ (r=−0.529 p<0.02) and ‘M1’ (r=0.477 p<0.05). Thus, markers of aerobic working capacity are negatively correlated with plasma viscosity and hematocrit, while the 4 mmol.l⁻¹ lactate threshold which measures the ability to avoid blood lactate increase is negatively correlated to RBC aggregation.