Current hydration guidelines are erroneous: Dehydration does not impair exercise performance in the heat

Authors

Bradley A. Wall, Edith Cowan University
Greig Watson, Edith Cowan University
Jeremiah J. Peiffer
Chris R. Abbiss, Edith Cowan UniversityFollow
Rodney Siegel
Paul B. Laursen

Document Type

Journal Article

Publisher

BMJ Group

Faculty

Faculty of Health, Engineering and Science

School

School of Exercise and Health Sciences

RAS ID

18414

Comments

Wall, B. A., Watson, G., Peiffer, J. J., Abbiss, C. R., Siegel, R., & Laursen, P. B. (2013). Current hydration guidelines are erroneous: dehydration does not impair exercise performance in the heat. British journal of sports medicine, bjsports-2013. Available here

Abstract

BackgroundLaboratory studies that support the hydration guidelines of leading governing bodies have shown that dehydration to only −2% of body mass can lead to increase in body temperature and heart rate during exercise, and decrease in performance. These studies, however, have been conducted in relatively windless environments (ie, wind speed

Aim To investigate the effect of blinded hydration status on cycling time-trial performance in the heat with ecologically valid facing wind speed conditions.

Methods During three experimental trials, 10 cyclists were dehydrated to −3% body mass by performing 2 h of submaximal exercise (walking and cycling) in the heat, before being reinfused with saline to replace 100%, 33% or 0% of fluid losses, leaving them 0%, −2% or −3% hypohydrated, respectively. Participants then completed a 25 km time trial in the heat (33°C, 40% relative humidity; wind speed 32 km/h) during which their starting hydration status was maintained by infusing saline at a rate equal to their sweat rate. The treatment was participant-blinded and the order was randomised. Completion time, power output, heart rate, rectal temperature and perceptual variables were measured.

ResultsWhile rectal temperature was higher beyond 17 km of the time trial in the −3% vs 0% conditions (38.9±0.3°C vs 38.6±0.3°C; p

Conclusion When well-trained cyclists performed a 25 km cycling time trial under ecologically valid conditions and were blinded to their hydration status, performance, physiological and perceptual variables were not different between trials. These data do not support the residing basis behind many of the current hydration guidelines.

DOI

10.1136/bjsports-2013-092417