Effects of carbohydrate supplementation on maximal intensity exercise performance

Recently, many studies have reported that the use of a carbohydrate (CHO) mouth rinse improves exercise performance lasting 30-60 min. Moreover, it has been reported that the presence of CHO in the mouth facilitates corticomotor excitability, while the ingestion of CHO improves maximal voluntary force production. Taken together, these findings raise the issue of whether CHO mouth rinsing with/without CHO ingestion could also improve sprint performance. This issue was recently addressed in a study we performed on overnight fasted competitive cyclists, with the finding that a 5-s mouth rinse with either maltodextrin or glucose had no significant effect on maximal sprint performance. One possible limitation with these findings was the short exposure time to the CHO mouth rinse solutions compared to other studies as well as the low CHO content of the mouth rinse solution. For these reasons, the purpose of the first study of this thesis was to determine whether intermittent mouth rinsing with a high concentration of glucose or artificial sweetener (aspartame) improves sprint performance compared to water. Our results showed that these treatments did not improve 30-s maximal cycling sprint performance. These findings, however, did not exclude the possibility that this negative result could be due to this stimulus being too weak to have an impact on performance. For this reason, the purpose of the second study of this thesis was to determine whether combining the ingestion of glucose with glucose mouth rinsing improves maximal cycling sprint performance compared to similar treatments using water, aspartame or maltodextrin. This study showed that this glucose treatment resulted in a marked ergogenic effect compared to the other treatments. Moreover, since the combined ingestion and rinsing of isoenergetic maltodextrin or sweetness-matched aspartame had no effect on any of the indicators of sprint performance, it was concluded that the ergogenic effect of the glucose treatment is unlikely to be related to a placebo effect or metabolism. Instead, these findings suggest that this ergogenic effect is probably mediated through the stimulation of glucose sensor cells in the gastrointestinal tract that are either unresponsive to aspartame or that trigger distinct signals to the brain compared to aspartame.