CARBOHYDRATE MOUTH RINSING IMPROVES EXTENDED PERFORMANCE WHEN INGESTION DOES NOT
Mauger, A. R., McGonagle, H., Taylor, L., & Castle, P. C. (2012). CHO mouth-rinse improves 16 km time-trial cycling performance in a glycogen depleted state. Presentation 2351 at the 59th Annual Meeting of the American College of Sports Medicine, San Francisco, California; May 29-June 2, 2012.
"Rinsing of carbohydrate solutions during exercise can improve performance in fixed work-amount cycle time-trials and automated treadmill running of ~45-60 min duration. Mechanisms responsible for this improved performance have been attributed to a reduced perceived exertion, activation of reward centers in the brain, and/or increased cortical excitability. However, this phenomenon has never been demonstrated in distance-based time-trial cycling, or when exercise is performed in a glycogen depleted state."
This study determined whether the central effect of carbohydrate mouth-rinsing during a 16 km cycling time-trial improved performance when muscle glycogen has been previously depleted. Recreationally active Ss (N = 8) completed a VO2max test, a 16-km familiarization time-trial, and four performance 16 km time-trials. The evening before each performance time-trial, Ss completed a previously described muscle glycogen depletion protocol and only ate a low-carbohydrate evening meal. During the performance time-trial, in a double-blind, randomized fashion, Ss either ingested or rinsed 150 mL of 6.4% glucose solution every two km, or ingested or rinsed 150 mL of commercially available non-caloric concentrate solution sweetened with aspartame and saccharin (placebo condition). Ss received no feedback during the time-trial other than distance completed. Measures of blood lactate, blood glucose, heart rate, rating of perceived exertion, and power output were recorded during each time-trial.
Time-trial completion was significantly reduced in the glucose-rinse condition versus the placebo-rinse condition. The 5% performance improvement in the glucose-rinse condition was accompanied by a mean 21 Watts higher power output in the first 12 km and a mean eight bpm higher heart rate throughout the time-trial. No changes in blood lactate, blood glucose, or rating of perceived exertion across the time-trials were observed. No significant differences were observed between the glucose-ingested, placebo-rinse, and placebo-ingested conditions.
Implication. Central changes and subsequent exercise performance improvement accompanying carbohydrate mouth-rinsing during exercise are apparent even when muscle glycogen levels have been previously depleted. [It should be noted that rinsing was more effective than drinking the glucose solution.]
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