Energy drinks work -- in
mysterious ways!
Wednesday, April 15,
2009
Runners clutching bottles of energy drink are a common sight, and
it has long been known that sugary drinks and sweets can
significantly improve athletes' performance in endurance events.
The question is how?
Clearly, 'sports' drinks and tablets contain calories. But this
alone is not enough to explain the boost, and the benefits are felt
even if the drink is spat out rather than swallowed. Nor does the
sugary taste solve the riddle, as artificial sweeteners do not
boost performance even when they are indistinguishable from real
sugars.
Writing in the latest issue of The Journal of Physiology, Ed
Chambers and colleagues not only show that sugary drinks can
significantly boost performance in an endurance event without being
ingested, but so can a tasteless carbohydrate – and they do so in
unexpected ways.
The researchers prepared drinks that contained either glucose (a
sugar), maltodextrin (a tasteless carbohydrate) or neither, then
carefully laced them with artificial sweeteners until they tasted
identical. They asked endurance-trained athletes to complete a
challenging time-trial, during which they rinsed their mouths with
one of the three concoctions.
The results were striking. Athletes given the glucose or
maltodextrin drinks outperformed those on 'disguised' water by 2 -
3% and sustained a higher average power output and pulse rate, even
though didn't feel they were working any harder. The authors
conclude that as-yet unidentified receptors in the mouth
independent from the usual 'sweet' taste buds must be responsible.
"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," explained Dr Chambers.
The team then used a neuro-imaging technique known as fMRI to
monitor the athletes' brain activity shortly after giving them one
of the three compounds. They found that both glucose and
maltodextrin triggered specific areas of the brain associated with
reward or pleasure, while the artificial sweetener did not. This
acts to reduce the athletes' perception of their workload, suggest
the authors, and hence enables them to sustain a higher average
output.
Their findings support the emerging 'central governor hypothesis' –
the theory that it is not the muscles, heart or lungs that
ultimately limit performance, but the brain itself, based on the
information it receives from the body. Stimulating the brain in
certain ways – such as swilling sugary drinks – can boost output,
perhaps giving athletes that all-important edge over their
rivals.
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Wiley-Blackwell
Thanks to Wiley-Blackwell for this
article.
