Relationships among body composition, hemorheology and exercise performance in rugbymen

We investigated relationships among body composition, blood rheology, and exercise performance in 14 rugbymen (19-31 yr, weight 65.8-109.2 kg, height 1.7-1.96 m, body mass index 21.7-33.1 kg/m2) who underwent a standardized submaximal exercise session on cycloergometer corresponding to 225 kJ over 30 min. The rheologic response to exercise was measured with the MT90 viscometer and the Myrenne aggregometer. Dehydration, evaluated by precision weighing, resulted in a loss of 360 to 973 g water, i.e., 1.69 to 4.32 g/kJ. This loss of water is not correlated to plasma volume contraction as assessed by the equation of Greenleaf. Hemorheologic changes are observed, but they are correlated neither to water loss, nor to plasma volume contraction. A 36% increase in blood viscosity (p < 0.01) is mainly explained by a red blood cell rigidification (p < 0.02), although hematocrit and plasma viscosity also increase (p < 0.01). Isometric adductor strength (specific ergometer) is correlated to erythrocyte flexibility (r = 0.680, p < 0.01). Red cell aggregability (Myrenne aggregometer) is correlated to fat mass measured by bioelectrical impedance (r = 0.634, p < 0.02). Aerobic working capacity index W170 is negatively correlated to the increase in plasma viscosity during exercise (r = -0.546, p < 0.05), suggesting that this event is less important in stronger individuals. This study shows that fat mass, even within a physiological range, is a determinant of erythrocyte aggregability, suggesting that training-induced alterations in body composition play a role in the specific hemorheologic profile of athletes. In addition, both erythrocyte flexibility and the magnitude of fluid shifts during exercise appear to be related to fitness in these sportsmen.