Blood metabolites during prolonged exercise in swimming and leg cycling.

This study was designed to compare the influence of two modes of exercise (swimming and leg cycling) on the blood concentrations of metabolic substrates and metabolites during a 45-min exercise period. Eight college students (mean age = 21.6 +/- 1.2 year) exercised at 70% of VO2 max, in water using the front crawl on one occasion, and on a cycle ergometer using the legs on another. Blood samples were drawn at 0, 15, 30, and 45 min and analyzed for free fatty acids, glycerol, glucose, pyruvate, and lactate concentrations. Mean oxygen uptakes (2.23 vs 2.12 l . min-1) and heart rates (152 vs 150 b . min-1) for cycling and swimming respectively were not significantly different. Lactate and pyruvate were significantly (p less than 0.01) higher during swimming as compared to cycling. Free fatty acids, glycerol, and glucose were not significantly different between the two modes of exercise (p greater than 0.05). Assuming venous blood concentrations provide some indication of metabolic events, these data are compatible with a tendency to a higher relative carbohydrate oxidation rate during swimming as compared to cycling during prolonged exercise at the same relative work intensities.