The significance of water in sport and weight control.

Intake of food and drink during exercise can be effective in enhancing performance, in so far as it prevents or ameliorates exercise-induced changes to body homeostasis. Loss of body fluids containing water and electrolytes during exercise is mostly by sweating. Sweat rates during a sporting event or activity will vary according to a number of factors, including the size of the athlete and his or her degree of acclimatization, the intensity of exercise, environmental conditions and the clothing worn. The mismatch of fluid intake and fluid losses may lead to a body water deficit. It has generally been considered that decreases in performance become apparent when hypohydration exceeds 2% of body weight; that performance decrements become substantial when fluid losses exceed 5% of body weight; and that when fluid losses approach 6-10% of body weight, heat stroke and heat exhaustion become life-threatening. Hypohydration also affects mental functioning. Therefore, the effect of hypohydration on real-life sport may be greater than that shown in laboratory studies of physiological performance.