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There are many types of commercially available sports drinks, but which is best for an athlete? Sports beverages fall into three classes, each with different uses.

A “sports drink” is any beverage formulated to rehydrate and replenish minerals and nutrients during exertion. Most commercially available sports drinks contain carbohydrates and electrolytes to help an athlete maintain a high level of performance over an extended period of time. Sports drinks can be hypotonic, isotonic or hypertonic formulations, depending on the concentration of minerals and carbohydrates in the beverage. Different formulations are intended for different situations. Hypertonic drinks should be consumed either several hours prior to exercise (so-called “carbohydrate loading”) or immediately after exercise, while isotonic and hypotonic drinks are best used during or immediately after exercise.

Classification of Sports Drinks

Hypotonic drinks: Sports drinks with less than 8% concentration of carbohydrate and minerals are hypotonic (lower particle concentration) compared to normal human body fluids. These drinks are absorbed rapidly from the intestine, and are good for rapid fluid replacement during and after exercise. These drinks are usually lower in calories than other types of sports drinks, and are therefore also suited for everyday consumption (unrelated to exercise).

Isotonic drinks: Isotonic sports drinks generally contain carbohydrates and electrolytes at 6-8% concentration. This concentration is similar to that of most normal fluids in the human body. Isotonic concentration allows for relatively rapid absorption of the ingested fluid from the stomach and small intestines. This allows for rehydration during exercise, and supplies fuel (simple carbohydrates) and electrolyes (critical for body function) to keep the athlete functioning at peak levels during endurance events.

Hypertonic drinks: Sports drinks with concentrations above 8% are hypertonic drinks. These drinks usually contain larger amounts of carbohydrates, which increases particle concentration. Hypertonic drinks are best used after long endurance events to replenish glycogen stores, or for “carbohydrate loading” in the days prior to an endurance event. Hypertonic fluids are absorbed more slowly than isotonic or hypotonic drinks - water is drawn into the intestine to dilute hypertonic drinks prior absorption. Therefore, hypertonic drinks are not appropriate for use during exercise, only several hours before or after exercise.

Appropriate Use of Sports Drinks

Each class of sports drink has an optimum use:

Hypotonic sports drinks: Examples – Water, Slazenger S1 – Hypotonic drinks are best used for rapid hydration. Most are lacking in electrolytes, and are therefore not optimum for exclusive use during long bouts of exercise (greater than 30 minutes).

Isotonic sports drinks: Examples – Gatorade, Powerade – Most commercially available sports drinks are isotonic. These drinks work well for longer exercise sessions, replenishing fluids, electrolytes and carbohydrates. These drinks are absorebd slightly slower than hypotonic drinks, and should be diluted for optimum use.

Hypertonic sports drinks: Example- Fruit juice – These drinks are best used after exercise, to boost muscle glycogen stores. They are not well suited for use during exercise, as they are slowly absorbed, and may cause cramping or bloating due to high particle concentration.