Compared with water, carbohydrate-only sports drinks have been shown to significantly reduce fatigue in a running test designed to simulate the running required in a soccer game, Davis said. Sports drinks also enhanced motor skills and mental performance, he said. Proper carbohydrate consumption before, during and after exercise also can be beneficial to the immune system, said David Nieman, a professor of health and exercise science at Appalachian State University. Although exercise generally strengthens the immune system, intense bouts such as competitions can weaken it. But carbohydrate sports drinks can substantially reduce immune system stress and reduce muscle inflammation, he said.
Sugar does it.
Staying hydrated before, during and after exercise, whether drinking water or a sports drink, is extremely important. Athletes need to drink as much as one liter of fluid an hour during exercise, but many only drink half that much, said Craig Horswell, who works in the physiology lab at Gatorade. Over several days you can develop chronic dehydration. In the past, some athletes weighed themselves to measure how much fluid they lost during exercise. If they lost 3 pounds, they would drink 3 pounds of fluids, about 48 ounces.