Journal Title (Medline/Pubmed accepted abbreviation): Nutr J
Page numbers: 33-36
doi (if applicable): 10.1186/1475-2891-9-33
Article type: Review (brief)
Summary of article:
The authors have written a brief review article (4 pages) summarizing the current state of research on the effect of carbohydrate mouth rinsing on endurance performance. The review summarizes the results of 6 major studies on this topic (Table 1 is an excellent overview of the studies). Of the 6 studies, two were done with running as the form of exercise and the remainder were of cycling. In all of the cycling studies, the workload was cycling at 75% of maximal power output for 1 h. In the running studies, one comprised running at 65% VO2 max for 15 min, followed by “self-paced” running for 45 min. The other consisted of running first at 60% of VO2 max for 10 min, followed by 30 min of running at a hard pace (rating of perceived exertion of 15 on Borg scale). In the cycling studies, mouth rinses were provided before and at increments of 12.5% of trial completion, while for the running studies, rinses were provided every 5-6 min. Essentially, a performance benefit was noted in 3 of 4 cycling studies and 1 of 2 running studies. The magnitude of the performance benefit, when observed, is generally a 2-3% improvement in performance (e.g., decreased time in a time trial on a bike, increased work output, or increase distance covered over a fixed time at a hard pace on a treadmill).
Interpretation of findings/Key practice applications:
The authors describe a study that explored the mechanism by which a carbohydrate mouth rinse, without ingestion, may improve performance. In that study, magnetic resonance imaging studies were performed and it was noted that supraspinal pathways of the brain were activated by either a glucose or maltodextrin rinse (6.4% in either case). These pathways were related to motivation and reward during exercise. One of the most surprising findings came from one cycling study in which there was either ingestion and mouth rinsing with the same carbohydrate dose. In that study, only the mouth-rinsing, not the ingestion, improved performance. The performance improvement was attributed to above mechanism coupled with lowered requirements for blood supply and energy cost for digestion of absorbed carbohydrate.
Another important point made by the authors is that, in the two studies that did not show improvements, subjects consumed a standardized diet followed by 2-4 hours of fasting. In the other studies, fasting periods were typically longer. They speculated that the nutritional status of the athlete (e.g., liver glycogen stores) might be an influential factor. However, it was noted that some studies still showed positive effects with as little as 3-4 hours of fasting, a time period that is generally too short to fully deplete liver glycogen. Sweetness did not appear to be an important factor, as 4 of the 6 studies used maltodextrin, 1 used sweetened maltodextrin, and only 1 fed glucose.