Energy Drinks Work -- In Mysterious Ways
ScienceDaily (Apr. 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.
Scand J Med Sci Sports. 2008 Nov 3. [Epub ahead of print]Click here to read Links
Mouth rinse but not ingestion of a carbohydrate solution improves 1-h cycle time trial performance.
Pottier A, Bouckaert J, Gilis W, Roels T, Derave W.
Department of Movement and Sports Sciences, Ghent University, Ghent, Belgium.
The aim of the present study was to further explore the influence of ingestion and mouth rinse with a carbohydrate-electrolyte solution (CES) on the performance during a approximately 1 h high-intensity time trial on trained subjects. Subjects rinsed around the mouth or ingested a 6% isotonic CES or placebo (14 mL/kg body weight) before and throughout a time trial in which they had to accomplish a set amount of work (975+/-85 kJ) as quickly as possible. In the mouth rinse conditions, time to complete the test was shorter (P=0.02) with CES (61.7+/-5.1 min) than with placebo (64.1+/-6.5 min), whereas in the ingestion conditions, there was no difference between placebo (62.5+/-6.9 min) and CES (63.2+/-6.9 min). Although power output and lactate concentration during exercise were significantly higher when subjects rinsed their mouth with CES compared with placebo, the rating of perceived exertion values did not differ. Blood glucose concentration increased after ingestion of but not after mouth rinse with CES. The interesting finding of the present study is that rinsing the mouth with but not ingestion of CES resulted in improved performance.
PMID: 19000099 [PubMed - as supplied by publisher]
Med Sci Sports Exerc. 2004 Dec;36(12):2107-11.Click here to read Links
The effect of carbohydrate mouth rinse on 1-h cycle time trial performance.
Carter JM, Jeukendrup AE, Jones DA.
Human Performance Laboratory, School of Sport and Exercise Sciences, The University of Birmingham, Edgbaston, B15 2TT, Birmingham, UK.
PURPOSE AND METHOD: To investigate the possible role of carbohydrate (CHO) receptors in the mouth in influencing exercise performance, seven male and two female endurance cyclists (VO(2max) 63.2 +/- 2.7 (mean +/- SE) mL.kg*(-1).min(-1)) completed two performance trials in which they had to accomplish a set amount of work as quickly as possible (914 +/- 40 kJ). On one occasion a 6.4% maltodextrin solution (CHO) was rinsed around the mouth for every 12.5% of the trial completed. On the other occasion, water (PLA) was rinsed. Subjects were not allowed to swallow either the CHO solution or water, and each mouthful was spat out after a 5-s rinse. RESULTS: Performance time was significantly improved with CHO compared with PLA (59.57 +/- 1.50 min vs 61.37 +/- 1.56 min, respectively, P = 0.011). This improvement resulted in a significantly higher average power output during the CHO compared with the PLA trial (259 +/- 16 W and 252 +/- 16 W, respectively, P = 0.003). There were no differences in heart rate or rating of perceived exertion (RPE) between the two trials (P > 0.05). CONCLUSION: The results demonstrate that carbohydrate mouth rinse has a positive effect on 1-h time trial performance. The mechanism responsible for the improvement in high-intensity exercise performance with exogenous carbohydrate appears to involve an increase in central drive or motivation rather than having any metabolic cause. The nature and role of putative CHO receptors in the mouth warrants further investigation.
PMID: 15570147 [PubMed - indexed for MEDLINE]
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