Current hydration guidelines are erroneous: dehydration does not impair exercise performance in the heat.
Wall BA, Watson G, Peiffer JJ, Abbiss CR Siegel R and Laursen PB. Br J Sports Med. 2013; [Epub ahead of print].
Take Home Message: Aerobic performance was not impacted by hydration status among 10 well-trained male cyclists during a 25 km time trial.
Current hydration guidelines promote optimal hydration levels in athletes to avoid hindering the athlete’s aerobic ability. These guidelines are based on studies with methodological issues such as the inability to blind patients to a treatment, which may lead to a placebo effect. Clinicians could optimize hydration protocols if we had a better understanding of how endurance athletes respond to various levels of dehydration. Therefore, Wall and colleagues examined the effect of intravenous infusion hydration status on 10 well-trained male cyclists performing a 25 km time trial. Participants (age: ~32 years, height: ~182 cm, body mass: ~81 kg) volunteered for the current study and maintained a regular training schedule. The authors required each participant to have 5 separate laboratory visits. On the first day the authors measured the participant’s body composition (via dual-energy X-ray absorptiometry), peak oxygen uptake, and workload. During the second testing session, participants completed a 25 km cycling time-trial from which sweat rate (mL/min) was calculated. At each of the remaining 3 trials, which were each separated by at least 6 days, participants completed a 25 km time-trial after following a dehydration protocol and one of three subsequent rehydration protocols. For each participant, the authors randomly assigned the order of the three rehydration protocols: 1) euhydration (infusion of 100% of the volume change experienced during the dehydration phase), 2% hypohydration (infusion of 33% of the volume change), and 3% hypohyration (infusion of 0% of the volume change). The authors completed all intravenous infusions within 90 minutes and blinded the participants to the amount of saline infused. Following the rehydration protocol, participants completed a 25 km time trial on a stationary ergometer and were instructed to complete the 25 km time trial as fast as possible. The authors measured power output and heart rate during the time trial while hydration level was maintained via continuous intravenous saline infusion which matched the sweat rate calculated during the second testing session. Overall, the mean time trial power output, time required to complete the trial, and heart rate were not different between any of the 3 testing conditions.
This study provides some interesting evidence that hydration level may not impact an endurance athlete’s performance as initially thought. Methodologically, this study was quite strong despite a small number of participants. While theoretically, the data presented here suggests that common levels of dehydration do not inhibit a cyclist’s aerobic ability, one must question how clinically applicable this data is at this point. The current study only applies to elite level cyclists and cannot be applied to other athletic populations without more extensive research. It may be beneficial if future research includes other athletic populations, acclimated and non-acclimated athletes, and various environmental factors. Overall, this study demonstrates that well-trained cyclists may adapt to mild hypohydration without compromising their performance, which may cause us to question the appropriateness of current hydration guidelines for this group of athletes.
Questions for Discussion: What hydration guidelines do you currently promote in your current practice? Have you found those guidelines to be especially effective in terms of aerobic performance?
Written by: Kyle Harris
Reviewed by: Jeffrey Driban
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