NUTRITION
July 25, 2008

Beat the Heat, Win the Meet

Need one more reason to stay hydrated while exercising in the heat this summer? Those fluids just might make you run faster and last longer.
Need one more reason to stay hydrated while exercising in the heat this summer? Those fluids just might make you run faster and last longer.

Multiple studies presented in June at the annual meeting of the American College of Sports Medicine add to the body of research suggesting a direct relationship between hydration and athletic performance, a relationship that is even stronger when it is hot.

Although elite athletes may have the most to lose from performance deficits associated with dehydration, the findings have important implications for everyone who exercises in the heat.

A 14-study meta-analysis by researchers at McGill University in Montreal found that in athletes who have lost at least 1.7% of their body weight, every additional percent loss of body mass is associated with 3% less power output.

A similar trend was seen in a University of Connecticut study in which 17 competitive distance runners completed four 12-km trail-running trials in heat averaging 26.5°C (80°F). Two trials were run under dehydrated conditions, created by restricting the athletes' fluid intake both before and during the run.

Two trials were run at a racing pace, and two at a slower, sub-maximal, pace.

In the dehydrated trials, the athletes had lost between 4.3% and 4.6% of their body mass on average, compared with 1.83% to 2.05% for the hydrated trials. When running at the racing pace, the athletes ran significantly faster when hydrated than when dehydrated (53.15 min vs 55.7 min). No performance effect was seen at the sub-maximal pace, but significant increases in core temperature and heart rate were observed under dehydrated conditions at both running speeds.

Although elite athletes may have the most to lose from performance deficits associated with dehydration, the findings have important implications for everyone who exercises in the heat. Experts say that recreational athletes and children tend to be the worst offenders when it comes to not drinking enough to replace the fluids lost through sweat during exercise.

A third study, from Harokopio University in Athens, Greece, confirms not only that staying hydrated improves performance in younger athletes, but that educating young people about the importance of hydration has a positive effect. Of 92 youth volleyball players enrolled in one of two five-day summer camps (average age was 14), 61 were part of an educational intervention that involved a lecture on hydration and bathroom charts explaining that darker urine signifies greater dehydration. The remaining athletes made up a control group. All athletes had access to fluids during the camps, as temperatures ranged from 25°C to 35°C (77°F to 95°F).

Two markers of hydration, urine specific gravity and urine osmolality, significantly improved in the educated group after two days, whereas no significant changes were seen in the control group. The better-hydrated athletes also shaved 22 seconds off their average 600-meter run time, while the average time for the control group essentially did not change.
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