Along with water as the primary ingredient, a sports drink contains carbohydrates (glucose, sucrose, fructose) and electrolytes (e.g., sodium).

Carbohydrates are the fuel of choice for working muscles. They prevent glycogen (carbohydrates stored in muscles) from being depleted too quickly. When muscle glycogen is depleted, limbs feel heavy, fatigue sets in and the athlete “hits the wall.” A sports drink can provide carbohydrates to help supply the muscles with quick energy and prevent the body from dipping into its glycogen stores.

Electrolytes help increase the absorption of fluid from the gut to the bloodstream. They also replace sodium lost through sweat and maintain plasma volume. A sports drink may contain other minerals, such as potassium and chloride. Although the amount of potassium lost through sweat is not large and can be replaced through normal diet, it may be helpful in preventing some muscle cramping.

A sports drink does a better job than water in staving off fatigue during high-intensity workouts lasting 60 minutes or during prolonged exercise (more than 90 minutes) A good sports drink will contain 5 to 8 percent carbohydrates, which amounts to 50 to 80 calories per 8 ounces (240 milligrams).

Avoid drinks too high in carbohydrates (e.g., soda, fruit juice). The extra carbohydrates can cause stomach discomfort and inhibit absorption of fluid into the bloodstream. Drinks with higher levels of carbohydrates are better consumed after a workout, rather than during exercise activities. This type of drink may cause cramping, gas and diarrhea.