The primary objective for replacing body water loss during exercise is to maintain normal hydration. To minimize risk of heat injury and impairment of exercise performance during exercise, water intake should attempt to equal fluid loss. At equal exercise intensity, the requirement for fluid replacement becomes greater with increased sweating during environmental heat stress.
To minimize the potential for thermal injury, it is advocated that water losses due to sweating during exercise be replaced at a rate equal to the sweat rate. Inadequate water intake can lead to premature exhaustion. During exercise, humans do not typically drink as much water as they sweat and, at best, voluntary drinking only replaces about two-thirds of the body water lost as sweat.
ACSM concludes it would be premature to recommend drinking something other than water during exercise lasting less than 1 hour. However, during intense exercise lasting longer than 1 hour, a sports drink containing carbohydrates can delay the onset of fatigue.
In addition, ACSM concludes that there is little physiological basis for the presence of sodium in an oral rehydration solution (for example, sports drink) for enhancing intestinal water absorption as long as sodium is sufficiently available in the gut from the previous meal.
A primary rationale for electrolyte supplements in sports drinks is to replace electrolytes lost from sweating during exercise greater than 4-5 h in duration.
However, if the presence of sodium enhances palatability, then ACSM find that its presence in a replacement solution may be justified because drinking can be maximized by improving taste qualities of the ingested fluid.
The American Academy of Pediatrics also found that children might be more likely to drink a flavored sports drink over water. Even though most children wouldn’t need the sports drink for their intended purpose, electrolyte replacement, sports drinks may encourage young athletes to increase fluid intake and stay hydrated.