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

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
Reviewed by: Jeffrey Driban

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Wall BA, Watson G, Peiffer JJ, Abbiss CR, Siegel R, & Laursen PB (2013). Current hydration guidelines are erroneous: dehydration does not impair exercise performance in the heat. British Journal of Sports Medicine PMID: 24055782