MURRAY, R., G. L. PAUL, J. G. SEIFERT, D. E. EDDY, and G. A. HALABY. The effects of glucose, fructose, and sucrose ingestion during exercise.Med. Sci. Sports Exerc., Vol. 21, No. 3, pp. 275–282, 1989. The purpose of this study was to compare the physiological, sensory, and exercise performance responses to ingestion of 6% glucose, 6% fructose, and 6% sucrose solutions during cycling exercise. Twelve subjects completed three sessions consisting of 115 min of intermittent cycle ergometer exercise at 65–80% of &OV0312;O2maxfollowed by a timed performance bout requiring the completion of 600 pedal revolutions. During each of five 4-min rest periods, subjects consumed 3 ml·kg LBM-1of one of the beverages. Beverages were presented in counterbalanced, double-blind fashion. Heart rate, &OV0312;O2, plasma urate, plasma lactate, respiratory exchange ratio, and carbohydrate combustion rates changed similarly among beverage treatments. However, fructose was associated with lower plasma glucose and serum insulin, a larger loss of plasma volume, greater gastrointestinal distress and relative perceived exertion ratings, and higher plasma or serum concentrations of free fatty acids, fructose, and Cortisol values than sucrose or glucose (P< 0.05). Compared to sucrose and glucose, fructose feeding also resulted in lower lactate and HR values during the performance bout (P< 0.05). Mean ± SE cycling performance times were faster with sucrose and glucose than with fructose: 419.4 ± 21.0 s, 423.9 ± 21.2 s, and 488.3 ±21.1 s, respectively (P< 0.05). Relative to 6% solutions of sucrose and glucose, ingestion of a 6% fructose beverage is associated with gastrointestinal distress, compromised physiological response, and reduced exercise capacity.