Blood viscosity responses to maximal exercise in endurance-trained and sedentary female subjects

To assess whether the rheological properties of blood might be altered by exercise, we measured whole blood viscosity, plasma viscosity, and its components in healthy female subjects before, immediately after, and 1 h after maximal upright exercise using the Bruce graded exercise protocol. Forty-seven female subjects (15 sedentary, 14 who ran 5-15 miles/wk, and 18 who ran greater than 50 miles/wk), ages 18-43 yr, were evaluated. Whole blood viscosity, measured with a cone and plate viscometer, increased an average of 12.6% with exercise. The increase was greater than can be attributed to the observed 8.9% increase in hematocrit alone due to a coincident increase in plasma protein concentration. However, plasma viscosity did not rise to the degree expected, likely due to a disproportionate observed loss of fibrinogen from the protein pool. These changes were independent of conditioning level or aerobic capacity. In this cross-sectional study, there appears to be no adaptive adjustment in females to physical conditioning that results in changes in blood viscosity.