Blood rheology and body composition as determinants of exercise performance in female rugby players

Athletes involved in rugby are characterized by a very specific pattern of body composition with an unusually important muscle mass. In a preceding study about rugbymen we evidenced that they exhibit a correlation between red blood cell aggregability and the amount of body fat although it remains within a normal range, and that red cell rigidity was correlated to isometric adductor strength. We had the opportunity of studying the relationships among exercise performance, body composition and hemorheology in 19 female rugby players (age 19-26, mean: 24.47 ± 0.67 yr) practising 4 - 10 hr/wk (mean 7.15 ± 0.3) since 1-12 yr (mean 4,05 ± 0,694). VO2max was not related by its own to blood rheology, either hematocrit (r = -0.0717 p = 0.7706) or plasma viscosity (r = 0.0144; p = 0.9533), but other markers of performance exhivited a correlation with red cell rheology. Relationships between fitness and body composition were evidenced. Isometric handgrip strength was negatively correlated to red blood cell aggregability (Myrenne M, r = -0.57839; p = 0.00948 M1 r = -0.58910; p = 0.00795). Adductor isometric strength was negatively correlated to red blood cell aggregability Myrenne M (r = -0.5033; p = 0.0280) but not to M1 (r = -0.4227; p = 0.0714). Fat mass is a major determinant of the maximal oxygen consumption VO2max either measured by a field test (r = -0.766; p = 0.00013) or exercise test (r = -0.575; p = 0.00994) and was also negatively correlated to both handgrip (r = -0.4918; p = 0.0325) and RBC aggregability M (r = -0.57839; p = 0.00948 and M1 r = -0.5891; p = 0.00795). Independently of fat mass, FFM appears to be a determinant of blood viscosity (r = 0.4622; p = 0.0463) due to its correlation with RBC rigidity (r = 0.4781; p = 0.0384). Thus, trained young women exercising 4-10 hr/wk and thus exhibiting a low percentage of body fat exhibit clear relationships between body composition and hemorheology, but fat mass being low, the parameter correlated with blood rheology is in this case fat-free mass, consistent with recent findings indicating that high fat mass in women is sometimes correlated with parameters of the metabolic syndrome such as insulin resistance or inflammation. In addition, parameters quantifying fatness even within such a physiological range are in this sample negatively related with exercise performance.