MITCHELL, J. B., D. L. COSTILL, J. A. HOUMARD, W. J. FINK, R. A. ROBERGS, and J. A. DAVIS. Gastric emptying: influence of prolonged exercise and carbohydrate concentration. Med. Sci. Sports Exerc., Vol. 21, No. 3, pp. 269–274, 1989. The purpose of this study was to examine the effects of serial feedings of different concentrations of carbohydrate (CHO) on gastric emptying and to compare the rates of gastric emptying at rest and during prolonged exercise. Solutions of 0, 6, 12, and 18 g·100 ml-1 (WP, CHO-6, CHO-12, and CHO-18, respectively) were tested. Ten trained male cyclists performed five trials involving 120 min of cycling. The first 105 min were at 70% of V̇O2max and the final 15 min were an all-out self-paced performance ride. In one of the five trials, the subjects rode intermittently, completing seven 15-min rides at 70% of V̇O2max, with 3 min of rest between each ride. Every 15 min, approximately 150 ml (8.5 ml·kg-·h-) of one of the four test solutions were consumed. (In the intermittent trial, the CHO-12 solution was used.) Subjects were also tested during 120 min of seated rest using the above feeding schedule (6% solution). Gastric residue was determined by stomach aspiration following the performance ride. The volumes emptied during the CHO-12 and CHO-18 trials (1,049.8 and 889.2 ml) were significantly different from each other and were less than during the WP and CHO-6 trials (1,210.3 and 1,185.6 ml) (P < 0.05). CHO delivery was significantly higher in the CHO-12 and CHO-18 trials (126 and 160 g) compared to the CHO-6 trial (71.1 g). There was no difference between the rate of gastric emptying for the resting and exercise conditions (9.5 vs 9.9 ml·min-1). These data indicate that 12 and 18% CHO solutions impair gastric emptying and fluid replacement but enhance CHO delivery. In addition, prolonged exercise did not alter the rate of gastric emptying compared to the resting condition.