Effects of carbohydrate ingestion on gastric emptying and exercise performance

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Abstract
In an effort to determine the effects of 5 (CHO-5), 6 (CHO-6), and 7.5 (CHO-7.5) percent carbohydrate solutions on gastric emptying and performance, 8 trained male cyclists performed 4 trials of intermittent (7- .times.; 12-min bout) cycling at 70% .ovrhdot.VO2max. A final 12-min self-paced ''''performance'''' ride was performed on an isokinetic ergometer (Fitron) interfaced with a computer to provide total work output. A water placebo (WP) was used as a control. Each 12-min ride was followed by 3-min rest, during which a drink was consumed (8.5 ml .cntdot. kg-1 .cntdot. h-1; mean total = 1336 ml .cntdot. 2 h-1). Blood samples were taken at 0, 25, 55, 85, and 115 min for blood glucose analysis. Following the performance ride, gastric residue was obtained by intubation and aspiration. Of the original 1336 ml ingested during each trial, the volumes emptied by the stomach for the four trials were 1306 .+-. 76, 1262 .+-. 82, 1288 .+-. 75, and 1278 .+-. 77 ml (.+-. SE) for WP, CHO-5, CHO-6, and CHO-7.5, respectively. Only the volume in the CHO-5 trial was significantly different from WP. The performance data showed that in all of the CHO trials, significantly more work was produced compared to the WP trial (CHO-5 = 1.98 .+-. 0.09 .times. 105 Nm; CHO-6 = 1.96 .+-. 0.09 .times. 105 Nm; and CHO-7.5 = 2.05 .+-. 0.13 .times. 105 Nm vs WP = 1.83 .+-. 0.11 .times. 105 Nm). There were no significant differences in performance between any of the CHO trials. Blood glucose in the water trial was significantly lower than in the CHO trials at 25 and 55 min, and was lower than in the CHO-6 and CHO-7.5 at 85 min. These data demonstrate that small serial CHO feedings are readily emptied and can enhance performance, possibly due to the maintenance of relatively higher blood glucose levels.