Researchers say you can spit out your sports drink and still boost performance

A few years ago, Asker Jeukendrup of the University of Birmingham, England, recruited a group of nine competitive cyclists and asked them to complete two simulated time trials of roughly an hour’s duration on stationary bikes. In one time trial, the subjects rinsed their mouths with a sports drink once every seven to eight minutes. The cyclists were not permitted to swallow the drink—they had to spit it out. In the other trial, they rinsed their mouths out with plain water.

Believe it or not, the cyclists completed the time trial almost two minutes faster, on average, when they rinsed their mouths with the sports drink as opposed to the plain water. Somehow the carbohydrate in the sports drink affected the cyclists’ performance without ever reaching their bloodstream. Jeukendrup hypothesized that the carbohydrate rinse activated carbohydrate receptors in the tongue, which stimulated the motor centers of the brain in a way that increased “central drive” to the working muscles, boosting muscle recruitment and performance. The simple presence of carbohydrate in the mouth at frequent intervals might have fooled the brain into believing that an extra source of energy was available, making it seem safe to work a little harder.

A more recent study led by Jeukendrup’s colleague Ed Chambers seems to confirm this hypothesis. In this study, trained endurance athletes completed a stationary bike time trial on three occasions, rinsing their mouths out at regular intervals with a glucose drink in one trial, a maltodextrin drink in another, and water flavored with artificial sweetener (so it contained no carbs) in a third. On average, the subjects completed the time trial 2 to 3 percent faster when rinsing their mouths with the glucose and maltodextrin drinks.

As a separate part of this study, the researchers used functional magnetic resonance imaging (fMRI) to look inside the subjects' brains as they tasted each of the three beverages. They found that the glucose and maltodextrin drinks activated a reward center of the brain while the artificially sweetened water did not. Combined with the time trial results, this is evidence that sports drinks enhance performance not only by supplying energy to the muscles when swallowed but also by reducing the perceived effort associated with a given level of exercise output when simply tasted.

Swish and Spit?
The practical implications of these findings are unclear. A carbohydrate mouth rinse certainly cannot entirely match the benefits of actually drinking a sports drink. In prolonged exercise, such as during marathon training or triathlon training, depletion of muscle glycogen stores and dehydration can cause fatigue. When it’s swallowed, a sports drink delays these causes of fatigue by providing an extra source of fuel to the muscles and by replacing some of the body fluid that is lost through sweating. When it’s merely spat out, a sports drink can’t do either of these things.

There may be some circumstances, however, when spitting out a sports drink may be beneficial. For example, athletes are generally not able to drink as much when running as they are when cycling, due to the stomach jostling involved. (Cyclists new to triathlon training often find this out quickly, and, at times, uncomfortably.) Consequently, runners are often unable to take in enough fluid to optimally limit dehydration and muscle glycogen depletion. It’s possible that runners could perform better in longer events like half-marathons and marathons by drinking at their maximum tolerable rate and then supplementing their drinking with regular sports drink mouth rinses. Asker Jeukendrup and colleagues may need to perform additional experiments to determine whether this tactic works for most runners. In the meantime, there’s no harm in trying it for yourself during your half-marathon training or marathon training!