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multi-hour cycling, Ironmans), getting down enough carbohydrate can be a serious gastointestinal challenge. That doesn't mean there's no role for rinsing and spitting, however. Beyond about two hours, your muscles really do need more carbohydrates, and you'll benefit from ingesting some. You can only fool the brain for so long. There are some conflicting results here, but the general picture seems to be not so much a "yes or no" effect, but rather a sliding scale where the strongest effects are observed in situations when you'd expect the body to be looking for more carbohydrates. Weaker effects, or sometimes no effect, are seen when subjects have eaten a carbohydrate-rich meal two hours before the exercise. In general, the strongest effects are observed for subjects who've just completed an overnight fast.
#SWISH AND SWALLOW FULL#
The effect seems to depend on how full of carbs you are when you start. The shortest exercise bouts to benefit appear to be about 30 minutes (although another recent study published since the review was completed observes effects in repeated 6-second sprints). In the review, Jeukendrup notes that these observations are consistent with the existence of a "central governor" that regulates motor output based on signals from the muscles - and from other places, including the mouth. Artificially sweetened (but carbohydrate-free) rinses don't produce the same effect, so it's not a taste thing, and it's not consciously mediated. Instead, it's the brain that's influenced by mouth rinsing: fMRI studies have shown that certain regions of the brain light up when you have carbohydrate in the mouth, whether it's sweet or tasteless. The muscles simply don't need it in such a short event.
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In this case, the cyclists actually could use the extra carbohydrate, but it had no effect on performance.
#SWISH AND SWALLOW TRIAL#
To drive this point home, Jeukendrup and colleagues did a study in 2004 where they infused glucose (or a saline placebo) directly into the veins of cyclists performing a 40-K time trial (which takes about an hour). Your body doesn't run out of carbohydrate during such short bouts, and the exercise is over before any significant amount of the extra carbohydrate you swallow is actually absorbed and oxidized. So what do we know about how this actually works? As Jeukendrup's review points out, there's no metabolic reason that carbohydrate ingestion should help during short bouts of exercise (e.g. In other words, the more they rinsed, the farther they cycled - and the easier it felt! Powerful stuff. Here's how much distance they covered in a 30-minute trial: Still, the most interesting comparison here was between the 5-second and 10-second groups. One obvious flaw here is that the "placebo" was water stronger experiments have used color- and taste-matched artificially sweetened drinks to act as a proper (indistinguishable) placebo. (3) rinse with sports drink for 10 seconds. (2) rinse with sports drink (6.4% carb) for 5 seconds So does contact time in the mouth matter? In the new study, the researchers compared three conditions: The suggested explanation was that the carbohydrate spent more time in the mouth during rinsing, and thus had more opportunity to stimulate sensors connected to the brain, than swallowing it. This one, by researchers at the University of Central Lancashire, digs into a practical detail: how long do you actually have to rinse to get benefits? It's an interesting question, because one study a few years ago found that rinsing and spitting a sports drink produced better results than actually swallowing the drink in a ~60-minute cycling time trial. But before I get to his conclusions, a quick look at another recent mouth-rinse study, published in the European Journal of Sports Science in April. In the new issue of Current Sports Medicine Reports, Asker Jeukendrup (one of the authors of the original 2004 study) reviews the existing literature to sum it up and look for patterns. People still have trouble believing it, but the research has been out there for nine years now: swishing a sports drink in your mouth and then spitting it out boosts performance in endurance events lasting longer than about 30 minutes.