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It is well known that dehydration negatively affects exercise performance and increases thermoregulatory strain during exercise. But athletes routinely experience moderate levels of dehydration in training and competition without any apparent loss of performance. Could it be that dehydration affects exercise performance less in trained than in untrained individuals?
Researchers from the University of Otago in New Zealand recently addressed this question in a study. Six trained and six untrained subjects each completed two exercise trials on separate occasions. In both trials they rode stationary bikes for 40 minutes at 70 percent of their maximum rate of oxygen consumption and then completed as much work as possible in 40 minutes. But they performed one trial in a dehydrated state and the other fully hydrated.
Interestingly, during the first moderate-intensity portion of the exercise trials, heart rate was significantly higher and drifted upward more in untrained subjects in the dehydrated trial as compared to the hydrated trial, whereas there was no difference between the two trials in trained subjects. Performance in the time trial portion of the exercise trials was negatively affected by dehydration for both groups, but the effect was twice as great for untrained subjects as for trained subjects.
These results, which were published in the journal Acta Physiologica, are not a license to go thirsty in workouts and races. No athlete, no matter how fit, is immune to or unaffected by dehydration. But it’s nice to know that the fitter you are, the better you can perform despite the unavoidable moderate dehydration that occurs in long workouts and races.