HARGREAVES, M., D. L. COSTILL, W. J. FINK, D. S. KING, and R. A. FIELDING. Effect of pre-exercise carbohydrate feedings on endurance cycling performance.Med. Sci. Sports Exerc., Vol. 19, No. 1, pp. 33–36, 1987. Six men were studied to compare the effects of pre-exercise carbohydrate feedings on endurance performance and muscle glycogen utilization during prolonged exercise. Trials consisted of a cycling ride to exhaustion at 75% maximal oxygen uptake preceded by the ingestion of either 75 g of glucose in 350 ml of water (GLU), 75 g of fructose in 350 ml of water (FRU), or 350 ml of an artificially sweetened and flavored placebo (CON). No differences were observed between trials for oxygen uptake, respiratory exchange ratio, heart rate, or exercise time to exhaustion (CON = 92.7 ± 5.2 min, FRU = 90.6 ± 12.4, and GLU = 92.8 ± 11.3, mean ± SE). Blood glucose was elevated as a result of the GLU feeding, but fell rapidly with the onset of exercise, reaching a low of 4.02 ± 0.34 mmol·1-1at 15 min of exercise. Serum insulin also increased following the GLU feeding but had returned to pre-drink levels by 30 min of exercise. No differences in blood glucose and insulin were observed between. FRU and CON. Muscle glycogen utilization during the first 30 min of exercise (CON = 46.3 ± 8.2 mmol·kg-1wet weight, FRU = 56.3 ± 3.0 mmol·kg-1wet weight, GLU = 50.0 ± 4.9 mmol±kg-1wet weight) and total glycogen use (CON = 93.4 ± 11.1, FRU = 118.8 ± 10.9, and GLU = 99.5 ± 4.3) were similar in the three trials. It was concluded that despite more stable blood glucose and insulin levels in FRU and CON, compared with GLU, no advantage to endurance performance or muscle glycogen utilization during prolonged exercise was provided.