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
$\dot{\mathrm{V}}$
O2max (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.
