Exercise scientists say they have stumbled on an amazing discovery. Athletes can improve their performance in intense bouts of exercise, lasting an hour or so, if they merely rinse their mouths with a carbohydrate solution. They don’t even have to swallow it.

It has to be real carbohydrates, though; the scientists used a solution of water and a flavorless starch derivative called maltodextrin. Artificial sweeteners have no effect.

And the scientists think they have figured out why it works. It appears that the brain can sense carbohydrates in the mouth, even tasteless ones. The sensors are different from the ones for sweetness, and they prompt the brain to respond, spurring on the athlete.

Many athletes depend on sugary beverages to keep them going. But often, when blood is diverted from the stomach to working muscles during intense exercise, drinks or foods cause stomach cramps. So a carbohydrate rinse can be a way to get the same effect.