Investigating the associations between hydration and exercise performance: methodology and limitations

Loss of body water, if sufficiently severe, impairs most physiological functions, but the body water content fluctuates over the course of a normal day with no implications for physical or mental performance. The point at which an effect of dehydration becomes apparent has been the subject of much debate, in part, at least, because of the different tests that have been applied, differences in the methodologies used to induce dehydration and also because of differences in the fitness and other physiological characteristics of the subjects studied. The act of drinking itself and the conscious denial of access to water will also have implications for subjective responses to the exercise task. In many published studies, it is difficult to separate the effects of ingestion of water from those of carbohydrate, electrolytes, and other drink components. Nevertheless, there is good evidence that drinking appropriate amounts of water, especially cold water, can enhance exercise performance in many situations.