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When we exercise, it is important to replace fluids in order to prevent dehydration. When we sweat, we release water from our cells and lose vital electrolytes such as sodium, potassium, magnesium, and calcium; and during hard exercise, energy stores in the form of carbohydrates.

Electrolytes conduct electricity in the body which allows for muscle contraction. Deficiency or an imbalance in just one of these electrolytes creates symptoms such as sluggishness, low energy, fatigue, and even muscle failure. Carbohydrate is stored as glucose in the liver and muscles and is the most efficient source of energy.

Rehydration following moderate exercise can be achieved by drinking water. However, activity involving extreme conditions such as climate, exercise intensity, and exercise duration (more than 60 minutes) requires more than just water to replenish the loss of vital electrolytes and energy stores. This is when sports drinks become a necessary component of your exercise kit.

Are All Sports Drinks Created Equal?

There is a wide range of sports drinks available for maintaining the fluid (water) or the fuel (glucose) plus some of the vitamins and electrolytes lost by the body during activity. Generally, sports drinks can be classed into one of three groups: isotonic, hypotonic, or hypertonic.

Isotonic drinks are used by many athletes including middle- and long-distance runners and those involved in active team sports such as soccer and hockey. Isotonic drinks contain water, some salt, and carbohydrates in the form of glucose–the body’s preferred source of energy–in a concentration of six to eight percent.

Hypotonic drinks can be used by athletes who need a quick fluid replacement without the energy boost provided by isotonic drinks. With less than three percent carbohydrates, hypotonic drinks enhance water absorption, but provide minimal energy. These can also be used before, during, and after exercise and may be useful if you are limiting your energy intake or have to drink very large amounts of fluid daily.

Hypertonic drinks are more concentrated (more than 10 percent carbohydrates) and are not recommended for consumption during exercise; although they provide energy, they delay the absorption of fluid into your body and may contribute to dehydration. However, during ultra-distance events or high-intensity activities where energy stores must be replaced during the event, hypertonic drinks may be used in conjunction with isotonic drinks to replace fluids.

Think Before You Drink

Sports specialists warn that, unless you are engaged in fairly strenuous activity or exercise of longer duration than about 60 minutes, drinking sports drinks can cause weight gain and electrolyte imbalance. Since many of these beverages contain 50 to 80 calories in an 8-ounce (236 mL) serving and are also high in citric acid, consuming too much can pack on extra pounds and erode tooth enamel.

Remember that sports drinks are meant as a replacement for those fluids, electrolytes, and energy stores that you use up during exercise, so choose wisely to suit your activity level.

Eric Viallagran, a former fitness instructor, is a natural bodybuilder and sport and nutrition enthusiast.

Source: alive #284, June 2006