15 April 2009

Sports drinks have mysterious effect

By
Cosmos Online
Athletes can boost their endurance levels simply by rinsing their mouths with a carbohydrate solution, rather than drinking it.
Man with sports drink

Sweet taste of success: A new study reports that the human brain can detect carbohydrates in the mouth and trigger reward signals that improve exercise performance. Credit: iStockphoto

SYDNEY: Athletes can boost their endurance levels simply by rinsing their mouths with a carbohydrate solution, rather than drinking it.

A new study, published in The Journal of Physiology, reports that the human brain can detect carbohydrates in the mouth and trigger reward signals that improve exercise performance. The authors say unidentified oral receptors are likely responsible for this effect.

Curiously, this means athletes need not even swallow sports drinks to get an energy boost.

Improved performance

“Much of the benefit from carbohydrate in sports drinks is provided by signalling directly from mouth to brain rather than providing energy for working the muscles,” said Ed Chambers, a co-author and researcher with the School of Sport and Exercise Sciences at the University of Birmingham in Britain.

For the study, the researchers gave endurance athletes a drink before having them complete a challenging bicycle ride. The drinks contained either a sugar (glucose), a tasteless carbohydrate (maltodextrin) or neither. All the drinks tasted the same due to the addition of artificial sweeteners.

Eight athletes completed the time-trial after rinsing their mouths with glucose water. Later, they completed the same time-trial after rinsing their mouths with the disguised regular water. Another eight underwent the same procedure with maltodextrin water.

When given the carbohydrate waters, athletes performed two to three per cent better than in the control time-trials. Though they didn’t feel as if they were working harder, they sustained a higher average power output and pulse rate.

Reward signals

The researchers then used imaging techniques to watch the athletes’ brains respond to the three different drink options. Both the glucose and maltodextrin caused activity in brain areas associated with reward and pleasure. Artificial sweeteners did not.

Chambers said the triggering of reward signals reduces the athletes’ perception of their workload, allowing for an improved performance. Because the effect is felt with both carbohydrates – but not with artificial sweeteners – these oral receptors may be independent from sweet taste buds.

These findings, he added, support the “central governor hypothesis” – the idea that it is not the muscles, heart or lungs that limit performance, but the brain itself.

Clyde Williams, a sports scientist with Loughborough University, also in Britain, said the new study builds upon others that have suggested the brain slows exercise after sensing low levels of carbohydrates. “The paper provides good evidence that simply having a carbohydrate solution in the oral cavity is detected by the brain,” he said.

Williams added the brain is responding to carbohydrates before they really enter the body. “In some ways the reaction is to the ‘promise’ of an incoming carbohydrate load,” he said, “and so one wonders what happens… when the ‘promise’ is not fulfilled.”

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