Fluid Loss

QUESTION: How do I know if I am getting enough fluid during exercise in hot weather?

 ANSWER: First and most important, DO NOT rely on thirst as an indicator to replace fluids. Fluid loss of 1-2% of body weight can compromise athletic performance; sensation of thirst usually does not occur until this or greater fluid loss has occurred. Fluid loss of 2-5% progressively increases risk of thermal injury and greater than 5-7% is usually associated with severe heat illness (heat stroke).

Fluid should be replaced early and frequently with cool water or sports drinks. Access to fluids should unrestricted (especially during team sports practices).

The best way to keep track of fluid is "pre- and post-exercise weights." A nude, dry weight should be checked just prior to exercise and a repeat weight should be checked immediately after exercise. The difference represents the exercise-related fluid loss. This should be completely replaced by the next exercise (either by the next day's exercise or with a "2-a-day" situation by the next practice). In conditions of chronic fluid loss, sports drinks, which include electrolyte replacement, should be used. Potassium-rich foods, such as bananas, should be increased in consumption. The normal American diet provides more than adequate replacement for sodium losses.

WRITTEN BY: Thomas K. Miller, M. D.