During exercise, water and certain minerals called electrolytes are expelled from the body through perspiration. The function of perspiration is to prevent body temperature from rising during exercise, which is important, but it comes at a cost, because water and electrolytes serve important functions within the body that they can no longer serve when they are lost. The more water the body loses, the less effective the “cooling system” of perspiration becomes. Meanwhile, the electrolyte minerals sodium, magnesium, and potassium are needed for a variety of processes ranging from nutrient transport to nerve transmission.

Consuming a sports drink containing water and electrolytes during exercise is an effective way to counteract the effects of sweating. However, it is impossible to restore fluid and electrolytes as quickly as they are lost during moderate- to high-intensity exercise. Athletes must therefore make up the balance by continuing to drink after completing exercise.

By weighing themselves immediately before and after workouts, athletes can determine the amount of fluid depletion they have experienced. They should drink at least this amount of fluid in the first 30 to 45 minutes after completing a workout.  Sports drinks are a better choice because they are formulated to replace water and electrolytes in approximately the same ratio in which they are lost in sweat.