Abstract

Eight healthy males were studied to compare the effects of pre-exercise fructose and glucose ingestion on muscle glycogen usage during exercise. Subjects performed three randomly assigned trials, each involving 30 min of cycling exercise at 75 V02max. Forty-five min prior to commencing each trial, subjects ingested either 50 g of glucose (G), 50 g of fructose (F), or sweet placebo (C). No differences in V02 or respiratory exchange ratio were observed between the trials. Blood glucose was elevated as a result of the glucose feeding. With the onset of exercise, blood glucose declined rapidly during G, reaching a nadir of 3.18 +/- 0.15 (SE) mmol/l at 20 min of exercise. This value was lower than tho corresponding values in F (3.79 +/- 0.20) and C (3.99 +/- 0.18). No differences in exercise blood glucose levels were observed between F and C. Muscle glycogen utilization was greater during G (55.4 +/- 3.3 mmol/kg w.w.) than C (42.8 +/- 4.2). No difference was observed between F (45.6 +/- 4.3) and C. There was a trend for muscle glycogen usage to be lower during F than G. These results suggest that the adverse effects of pre-exercise glucose ingestion rare, in general, not observed with either fructose or sweet placebo. Verf.-Referat