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Sports Science Update: Spit Out Your Sports Drink

  • By Matt Fitzgerald
  • Published May. 12, 2010

Recent studies show you need not swallow your sports drink to benefit from it.

Written by: Matt Fitzgerald

We all know how the carbohydrate content in sports drinks benefits running performance. Those carbs are quickly absorbed through your intestine and into your bloodstream, which then carries them to your working muscles to be used as an extra fuel source. Very simple.

Except it’s not so simple. A recent sequence of studies led by Asker Jeukendrup at the University of Birmingham, England, threatens to radically transform our understanding of how sports drinks work. In these studies, Jeukendrup has shown that simply rinsing the mouth with and spitting out a sports drinks enhances running performance as much as actually swallowing it.

In a new summary of this research published in Current Opinion in Clinical Nutrition and Metabolic Care, Jeukendrup writes, “This would suggest that the beneficial effects of carbohydrate feeding during exercise are not confined to its conventional metabolic advantage but may also serve as a positive afferent signal capable of modifying motor output.”

More specifically, it appears that the human tongue contains specialized carbohydrate receptors that communicate directly with the brain in ways that reduce perceived effort during exercise. And since, as the recent work of Samuele Marcora proves, the limits of endurance performance are defined by the maximum tolerable effort, the reduction in perceived effort caused by the presence of carbohydrate on the tongue allows the runner to run faster before reaching that threshold.

This discovery is good news for runners who struggle to keep fluids down during longer races, as it allows them to enjoy some of the performance benefits of using a sports drink without even bothering to try to keep it down.

I say “some of the benefits” because it is unlikely that carbohydrate mouth rinsing will prove to be a complete substitute for sports drink consumption during longer races, for two reasons. First, in longer races, actual glycogen (or muscle/liver carbohydrate) depletion can limit performance. I doubt that carbohydrate mouth rinsing can completely counteract simply running out of gas. While Jeukendrup’s studies seem to demonstrate that sports drinks do not allow runners to run faster over moderate distance by metabolic means, but instead by neurological means, I suspect that it is primarily through metabolic means (specifically, by actually supplying fuel to the muscles) that sports drinks enable runners to go farther at any given pace.

Second, dehydration also may limit performance in longer races, and carbohydrate mouth rinsing does not hydrate.

But these are only speculations. I would be very interested to see how carbohydrate mouth rinsing compared against sports drink consumption in affecting performance in a full marathon. Any volunteers?

[sgi:MattFitzgerald]

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Matt Fitzgerald

Matt Fitzgerald

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