The aim of the present study was to investigate potential mechanisms responsible for the improvement in prolonged exercise capacity in hot environments with exogenous carbohydrate. Eight endurance-trained men (VO2max 60.5 ± 2.4 ml·kg-1·min-1, mean ± SE) cycled to exhaustion on three occasions at 60% VO2max at an ambient temperature of 35 °C. They ingested either a sweet 6.4% carbohydrate solution (SC), a nonsweet 6.4% carbohydrate solution (NSC), or water (W). Exercise capacity was significantly increased with SC and NSC compared to W, the improvements corresponding to 15.8% and 11.8%, respectively. No difference in exercise capacity was seen between SC and NSC solutions. Plasma glucose concentrations were higher during the SC and NSC trials compared to W, significantly so at 10 min and at fatigue. Rates of carbohydrate oxidation were higher in the SC and NSC trials, although the rates never declined below 2.1 ± 0.2 g·min-1 in the W trial. There was no difference in the rate of rise of rectal temperature between trials, but there was a trend for subjects to fatigue at higher temperatures during the two carbohydrate trials. In conclusion, exogenous carbohydrate, independent of sweetness, improves exercise capacity in the heat compared to water alone.
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