Abstract

During prolonged exercise in the heat, people can become dehydrated at a rate of 1-2 1/h due largely to water losses in sweat. Recent evidence demonstrates that the resulting progressive dehydration will cause significant cardiovascular, metabolic,
thermoregulatory and endocrine disturbances that might lead to early fatigue, heat-related injury or even death. During exercise in the heat, the degree of hyperthermia, the rise in heart rate and the decline in cardiac output are directly proportional to the magnitude of dehydration. These negative effects of dehydration are common to different modes and intensities of exercise. Ingesting a volume of fluid equal to sweat loss will completely prevent these alterations in body function due to dehydration. Based on a strictly physiological point of view, it is therefore clear that people should attempt to ingest a volume of fluid that fully matches the rate of dehydration during exercise in the heat. However, from a competitive point of view, athletes should find their optimal fluid replacement scheme by pondering
the physiological benefits of drinking large volumes of fluid during competition, namely the likely improvement in exercise speed during the last stages of the race or match, and the practical drawbacks of having to slow down while drinking and while possibly suffering gastrointestinal discomfort. To ensure the maximum benefit of ingesting large volume of fluids during exercise and reducing or preventing its drawbacks, athletes should practice drinking during their daily workouts.