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The Effect of a Carbohydrate Mouthwash on Exercise Performance

Nutritional strategies are one of a plethora of means by which athletes seek to enhance performance (Applegate & Grivetti, 1997). Carbohydrates (CHO) are believed to be of particular importance to an athlete’s diet (Coyle, 2004). This is emphasised by a joint position statement of the American College of Sports Medicine, the American Dietetic Association, and the Canadian Dietetic Association (2000) on nutrition for athletic performance, making numerous recommendations for CHO specifically. It is generally accepted that CHO supplementation during prolonged (>2 hours) exercise can delay fatigue and improve performance (Jeukendrup, 2004). The mechanisms responsible for the improvement in performance are thought to be attributed to maintenance of blood glucose concentrations and CHO oxidation rates (Coyle, Coggan, Hemmert, & Ivy, 1986), and the sparing of liver and muscle glycogen stores (Tsintzas & Williams, 1998).

Some studies have also shown that CHO ingestion during relatively high intensity [>75% of maximum oxygen uptake ( 2max)] short duration (~1 hr) exercise can improve performance (Ball, Headley, Vanderburgh, & Smith, 1995; El-Sayed, Balmer, & Rattu, 1997; Jeukendrup, Brouns, Wagenmakers, & Saris, 1997). However, the mechanism by which this improvement occurs is unknown. Jeukendrup et al. (1997) estimated that only 5-15 g of exogenous CHO is oxidised during the first hour of exercise. This amount is thought to be too small compared to the total CHO oxidised to significantly affect performance. This led some authors to suggest that CHO has a non-metabolic effect (Ball et al., 1995; El-Sayed et al., 1997; Jeukendrup et al., 1997). Interestingly, intravenous glucose infusion did not improve 1-hr cycle time-trial performance despite high availability of CHO for oxidation (Carter, Jeukendrup, Mann, & Jones, 2004a). These findings support the notion that improvements in performance are not associated with increased availability of blood glucose, indicating a possible role of the mouth and gastrointestinal track in CHO supplementation. This seems plausible as the mouth and gut are thought to be important in perceptions of thirst during exercise; Maresh et al. (2001) reported lower RPE and sensations of thirst with oral rehydration in comparison to intravenous rehydration during exercise in the heat.

Carter, Jeukendrup, and Jones, (2004b) examined the effect of a CHO mouthwash on 1-hr cycle time-trial performance. The cyclists rinsed either a CHO or placebo solution in their mouths at regular intervals throughout the duration of the time-trial. This enabled the researchers to examine any potential central effects of CHO, without the influence of its metabolic effects. The CHO mouthwash improved time-trial performance by 2.9% (1 min and 48 s) compared to the placebo trial. The findings of this study led the authors to speculate that CHO may trigger receptors in the oral cavity activating pleasure centres in the brain and improving central drive to the working muscles.

Future research should continue to assess the role of the mouth in CHO supplementation, in order to gain a more complete understanding of the complex mechanisms by which exogenous CHO improves high intensity short duration performance.

References:

American College of Sports Medicine, American Dietetic Association, & Dietitians of Canada. (2000). Joint position statement. Nutrition and athletic performance. Medicine and Science in Sports & Exercise, 32, 2130-2145.

Applegate, E. A., & Grivetti, L. E. (1997). Search for the competitive edge: a history of dietary fads and supplements. Journal of Nutrition, 27, 869S-873S.

Ball, T. C., Headley, S. A., Vanderburgh, P. M., & Smith, J. C. (1995). Periodic carbohydrate replacement during 50 min of high-intensity cycling improves subsequent sprint performance. International Journal of Sport Nutrition, 5, 151-158.

Carter, J. M., Jeukendrup, A. E., Mann, C. H., & Jones, D. A. (2004a). The effect of glucose infusion on glucose kinetics during a 1-h time trial. Medicine & Science in Sports & Exercise, 36, 1543-1550.

Carter, J. M., Jeukendrup, A. E., & Jones, D. A. (2004b). The Effect of Carbohydrate Mouth Rinse on 1-h Cycle Time Trial Performance. Medicine & Science in Sports & Exercise, 36, 2107-2111.

Coyle, E. F. (2004). Fluid and fuel intake during exercise. Journal of Sports Science, 22, 39-55.

Coyle, E. F., Coggan, A. R., Hemmert, M, K., & Ivy, J. L. (1986). Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. Journal of Applied Physiology, 61,165-172.

El-Sayed, M. S., Balmer, J. & Rattu, A. J. M. (1997). Carbohydrate ingestion improves endurance performance during a 1 h simulated cycling time trial. Journal of Sports Sciences, 15, 223-230.

Jeukendrup, A. E. (2004). Carbohydrate intake during exercise and performance. Nutrition, 20, 669-677.

Jeukendrup, A. E., Brouns, F., Wagenmakers, A. J. M., & Saris, W. H. M. (1997).Carbohydrate feedings improve 1 H trial cycling performance. International Journal of Sports Medicine, 18, 125-129.

Maresh, C. M., Herrera-Soto, J. A., Armstrong, L. E., Casa, D. J., Kavouras, S. A., Hacker, F. T., et al., (2001). Perceptual responses in the heat after brief intravenous versus oral rehydration. Medicine and Science in Sports & Exercise, 33, 1039-1045.

Tsintzas, K., & Williams, C. (1998). Human muscle glycogen metabolism during exercise: Effect of carbohydrate supplementation. Journal of Sports Medicine, 25, 7-23.