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Isotonic sports drinks are designed to help replenish the body after prolonged activity. Isotonic drinks contain small amounts of sugar and salt, similar to the salt and sugar concentrations of the human body. They replace fluids and salts lost to exercise and help replenish glycogen stores.
The carbohydrates in isotonic sports drinks are simple sugars. The drinks typically contain from 5 percent to 8 percent sugar. This glucose replaces the body's energy reserves and is often used by endurance athletes to help with hydration and performance. Many isotonic sports drinks also are infused with vitamins and minerals, such as potassium, magnesium, and calcium.
Isotonic drinks help to replace electrolytes, which assist in pH balance maintenance and control the body’s fluid levels. Electrolytes are lost through perspiration and respiration and are vital to performance and overall health. Athletes use isotonic sports drinks that replace electrolytes — especially after exercising in extreme conditions or for prolonged periods of time — to avoid dehydration.
Sports drinks are typically broken down into three categories: hypertonic, hypotonic, and isotonic. Hypertonic drinks contain more salts and sugars than the other types of sports drinks, and provide extra glucose to the body to meet extreme energy demands. Hypotonic drinks contain fewer electrolytes and sugars, and are used by athletes who don’t need extra carbohydrates. Isotonic sports drinks, the most common variety, contain nutrient concentrations that are in balance with the body and are, therefore, easily assimilated.
Sports scientists at the University of Edinburgh in Scotland conducted studies of isotonic sports drinks on teens. The adolescent subjects were able to perform high-intensity exercise up to 24 percent longer when consuming a sports drink. The researchers concluded that a 6 percent carbohydrate electrolyte solution improved athletic endurance but had no effect on speed.
Commercial isotonic sports drinks are widely available, as are many homemade versions. Recipes usually consist of a small amount of fruit juice, water and salt. For example, 17 ounces (500 ml) of natural fruit juice can be mixed with an equal measure of water and a pinch of salt to make a homemade version of an isotonic drink. Another mixture can be made by combining 7 ounces (about 200 ml) of mashed fruit with 28 ounces (about 800 ml) of water and a pinch of salt.
Hydration is key to sports performance, and athletes can use isotonic sports drinks to help meet fluid consumption needs. When from 3 percent to 6 percent weight loss occurs through water loss during exercise, severe cramping and performance loss can result. Weakness, disorientation, and lethargy are side effects of dehydration and electrolytes loss. Isotonic drinks enable athletes to perform longer and combat the effects of dehydration.