Hemorheological response to prolonged exercise--no effects of different kinds of feedings

Thirty-one male triathletes performed three experimental trials at one week intervals, with either a semi-solid or liquid carbohydrate feeding, or a liquid placebo. Exercise consisted of three hours of alternately cycling, running, cycling, and running at 75% VO2 max. Venous blood samples were taken before and immediately after the exercise. Viscometry was performed with a Contraves LS-30 viscometer and erythrocyte deformability was measured with the LORCA, a laser diffractometric system. Exercise caused a significant increase in whole blood and plasma viscosity, hematocrit, and osmolality, and a very small, but significant decrease in erythrocyte deformability, irrespective of the feedings consumed. Changes were not related to exercise performance, as defined by the maximal test time, probably due to a large fluid intake. The intake of different amounts of carbohydrate had no influence on the hemorheological parameters, probably since water content was equal among feedings. Erythrocyte deformability changes were small in comparison with the other hemorheological changes and a correlation between erythrocyte deformability and other parameters was absent. This may be due to erythrocyte properties to counterbalance volume shifts to ensure an optimal oxygen delivery in the microcirculation.