Could sloshing sugar water around in your mouth and then spitting it out provide a crucial advantage for athletes? In recent years, sports scientists have found convincing evidence that a “carbohydrate mouth rinse” AKA “carb-rinsing” can help athletes perform better. Several studies have reported that, after rinsing, athletes lift more weight, run faster and farther, jump higher and are more focused. The possible reason for this: the brain gets fooled into thinking that the body has just been given more energy.
A study published last year in the European Journal of Sport Science found that carb-rinsing boosted a range of performance measures. The researchers, from Coventry University, tested 12 healthy men in their early or mid-20s and found that carb-rinsing significantly improved jumping height, the number of bench presses and squats, sprint times over 10 meters, and their sense of alertness.
In December, researcher Trent Stellingwerff published a study of carb-rinsing among a group of athletes, and found that it significantly increased peak power in a series of leg exercises. The results were surprising, says Stellingwerff, who is the director of research at the Canadian Sport Institute, the country’s Olympic research facility in Vancouver. “We were really shocked. The rinse has an instantaneous effect. It allows subjects to perceive that the task is easier.”
Ingesting carbs may also improve performance. But doing so during training or competition can cause intestinal problems, which is definitely not conducive to peak performance.
The effect of rinsing is disputed – some studies have not found any effect. In a study published last year by Greek and South African scientists, 15 female runners ran two 60-minute races. Each subject ran one race after rinsing with a carb solution, and one after rinsing with a placebo. The carb solution made no difference in their times. Of course, they may have run the wrong kind of race: some researchers theorise that carb-rinsing may help with quick, explosive activities such as sprinting and lifting weights, but not in endurance events.
The mechanism underlying carb-rinsing remains unclear: nerves in the mouth are closely linked to many key brain areas, and some scientists think that these nerves send powerful messages to brain areas that control motivation, motor control and pain tolerance. So even if the body gets no actual energy boost from the carb water, simply a transient sensation, the rinse may activate the brain, boosting strength and endurance. The rinse persuades the brain to accept an illusion – an illusion that the brain then acts on, leading to a real-world rise in performance.
“When you carb-rinse, it activates the reward and arousal areas of the brain,” says Neil Clarke, a sports and exercise scientist at Coventry University. “The brain expects a carbohydrate boost, so it gets aroused. You’re almost tricking the brain. The brain says: ‘OK, carbs are on the way, we can push harder now.’”
Clarke says the process appears to be subconscious. In the study last year of men in their 20s, he and his colleagues used maltodextrin as the carbohydrate; maltodextrin has no taste, so the subjects in the study didn’t know, at least consciously, that the liquid was any different than the unsweetened control liquid. Despite its tastelessness, the maltodextrin solution improved subjects’ athletic performance. Overall, he reckons, carb-rinsing improves performance by about 2% to 3%.
This may not sound like much, but at the elite level, the margins are stunningly slim, and a seemingly small change can mean the difference between a gold medal and last place. For an elite marathoner, improving a time by 3% would slice about four minutes from his or her time. For a world-class 100-metre sprinter, this would cut a third of a second, also an enormous amount. For instance, in the 2016 Olympic 100-metre final, Usain Bolt won with a time of 9.81 seconds. Travon Mitchell came in eighth with a time of 10.06 – a quarter-second gap. Maybe if Mitchell had carb-rinsed before the race, he’d have won gold.