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
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.
Source : Wiley-Blackwell