May 14, 2015
Study Questions Dehydration’s Effect on Performance

A recent Canadian study indicates that dehydration may not affect physical performance as previously thought. The researchers emphasized, though, that dehydration still stresses the body and can cause negative effects at a severe level.

According to The Canadian Press, the study was conducted at Brock University in St. Catharines, Ontario, and led by Stephen Cheung, PhD, Professor of Kinesiology at the school. Using a group of 11 competitive cyclists and trathletes, researchers had the subjects cycle for 90 minutes in a hot-dry chamber set at 35 degree Celisius while hooked up to an IV. Some received saline to replace the fluids they sweated out while others did not. Neither the cyclists nor the researchers knew which riders were in which group.

After a 10-minute break, the cyclists completed a 20-kilometer time trial and asked to go as hard as they could. The researchers found there was no difference between the performance of those who had received fluids and those who had not, despite those not being hydrated losing more than two percent of their bodyweight. Cheung noted that the results reflect the practice of elite marathon runners who often do not drink much during their races.

“You can, for a short term, tolerate dehydration and still perform very well,” Cheung told The Canadian Press “Your body is more stressed with dehydration. So no questions there. But the performance was not different. And also none of these competitive elite athletes were at any (health) danger.”

The study also looked at the effect of thirst on performance by allowing some riders to rinse their mouth, and this also resulted in no difference in performance levels. Titled “Separate and combined effects of dehydration and thirst sensation on exercise performance in the heat,” it appears in the June issue of the Scandinavian Journal of Medicine and Science in Sports, and is part of a special issue on training and competing in heat.

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