Gaudard, A., Varlet-Marie, E., Bressolle, .F, Mercier, J., & Brun, J. F.(2003). Hemorheological correlates of fitness and unfitness in athletes: moving beyond the apparent "paradox of hematocrit"? Clinical Hemorheology Microcirculation, 28(3), 161-173.

Negative correlations between blood viscosity parameters and fitness have been reported, but their physiological meaning remains incompletely understood. Since rheo-active treatments are used in sport doping, it would be useful to clarify the relationships between hematocrit (Hct), viscosity, and performance by comparing aerobic capacity, responses to an overtraining questionnaire, and hemorheological parameters. Sportsmen (N = 29) performed a standardised exercise test. Physical working capacity (W170), maximal power output, and maximal oxygen consumption (VO2max) were calculated.

The best significant correlate with maximal power output was whole blood viscosity (r = -0.383). A stepwise regression analysis selected hematocrit as the only determinant of physical working capacity (r = -0.66,). The best determinant of VO2max, expressed as a percentage of theoretical values, was hematocrit (r = -0.462. The hematocrit/viscosity ratio, a proposed index of hematocrit's positive influence on O2 transfer to tissues, was positively correlated to maximal power output expressed as a percentage of theoretical values (r = 0.487. The overtraining score was correlated to plasma viscosity (r = 0.450).

Implication. The best hemorheogical correlate of fitness is a low hematocrit and the best hemorheological correlate of overtraining is increased plasma viscosity.

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