Effects of endurance training and long distance running on blood viscosity.

The effect of endurance training on blood viscosity was studied by comparing blood rheological properties in control subjects (untrained) and endurance trained subjects. The effect of running on blood viscosity was studied in the 33 endurance trained subjects before and after a 48-km mountain race (Sandia Wilderness Crossing Research Run). Runners started at an altitude of 1700 m, ran 26 km to 3300 m, then descended 22 km to finish at 1900 m. Venous blood viscosity (eta b) and plasma viscosity (eta p) were measured at 37 degrees C at shear rates of 11.25, 22.5, 45, 90, and 225.s-1, using a cone-plate viscometer. Endurance trained subjects had significantly higher pre-race blood viscosity at 11.25 and 22.5.s-1 than control subjects but similar plasma viscosity and hematocrits. Following the race, there was no significant change in mean hematocrit, but eta b increased significantly at all shear rates except 225.s-1. Plasma viscosity at 225.s-1 increased significantly from 1.44 to 1.53 cP following the run. Since eta b did not increase, an increase in red cell deformability is inferred. The mechanism of the increase in eta b at lower shear rates in runners is due in part to the higher plasma viscosity. An additional mechanism at lower shear rates is in an increase in red cell aggregation. Increased plasma fibrinogen was measured in six of six resting subjects taken from 1600 m to 3300 m and is speculated to be the mechanism of enhanced aggregation and deformability in the runners.