Sports drinks' dirty little secret is just plain sugar: study

[Source: Ottawa Citizen, April 18, 2009]

Swish-and-spit method works just as well as swallowing, experts find

By Tom Spears


Sports-medicine resear-chers in Britain have found out why sugary "energy drinks" help endurance athletes, and along the way they've thrown out all the reasons people usually think of.

Runners and cyclists sometimes credit the calories, or the burst of blood sugar, or caffeine, or electrolytes, or the fluid itself.

Wrong to all those, says the University of Birmingham team. They know these can't be the reason, because rinsing and spitting with energy drinks turns out to improve performance as much as drinking them.

Instead, they found a second performance-enhancing mechanism: The presence of sugar, and sugar alone.

And this opens up whole new avenues of understanding human endurance, coming just a month before thousands of runners will run in the Ottawa Race Weekend (May 23-24).

Ed Chambers, a PhD student at the School of Sport and Exercise Sciences at Birmingham, prepared drinks that contained either glucose (a sugar), maltodextrin (a tasteless carbohydrate) or neither. He then added artificial sweeteners until all three mixes tasted identical.

Then he asked cyclists with experience in endurance races to race through time trials, during which they rinsed their mouths with one of the three concoctions.

No one swallowed anything.

Cyclists who swished with glucose or maltodextrin drinks outperformed those on saccharin and water by two to three per cent, sustaining a higher average power output and pulse rate, even though they didn't feel they were working any harder.

Sweet taste alone can't be the reason, since all the drinks were sweet, the researchers conclude in an article in the Journal of Physiology. They believe there's another set of undiscovered receptors -- cells that sense things -- in the mouth.

"Much of the benefit from carbohydrate in sports drinks is provided by signalling directly from mouth to brain rather than providing energy for the working muscles," Chambers wrote in a summary of his work.

The British research adds to an idea floated four years ago in another sports medicine journal, which is that the brain -- not the muscles, heart or lungs -- is the factor that limits the endurance of the body.

Three South Africans noted in 2005 that the usual theory says muscles reach their limit "usually as the result of either an inadequate oxygen supply to the exercising muscles or total energy depletion in the exhausted muscles."

Instead, they proposed, the brain acts like the governor on a car or truck engine, limiting how hard the muscle can work in order to prevent damage.

"The brain paces the body during exercise specifically to ensure that the preplanned activity is completed" without upsetting the normal muscle cell function, the University of Cape Town team wrote in the British Journal of Sports Medicine. The brain does this, they said, by changing the signals it sends to muscles, and through "the increasingly disagreeable sensations of fatigue that are generated by the brain during exercise."

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