(MONEY Magazine) – It's summertime, and the sportin' is sweaty. So, aerobic animal that you are, you may be tempted to quaff Quaker Oats' top-selling Gatorade (89 cents for a 16-ounce bottle), Pepsi's new All Sport (also 89 cents), Twin Lab's costlier Hydra Fuel ($1.25) or one of no fewer than 10 other popular fluorescent, fluid-replenishing sports drinks. In all, Americans guzzled $870 million worth of the liquids last year, up from $625 million in 1990, according to New York City research firm Packaged Facts. But don't pop the top just yet. According to manufacturers of the 13 national sports drink brands -- up from about seven two years ago -- these concoctions contain carbohydrates, electrolytes and often minerals that help your body recover from the effects of exercise more quickly than water can alone. But nutritionists say that unless you're among the fewer than 10% of Americans who exercise strenuously for more than an hour a day, drinking a free quart of H2O for every hour you exercise does the job just as well. It's true that you need carbohydrates to refuel your muscles when they run low on glycogen, the body's prime energy source. But Auburn University nutrition professor Bob Keith explains that muscles normally store 60 to 90 minutes' worth of the complex carbohydrate. In addition, a balanced diet provides plenty of the electrolyte sodium, which helps water pass quickly from the small intestine to the rest of the body. Bill Fink, a physiologist at Ball State University in Muncie, Ind., concludes that "it's difficult if not impossible to demonstrate that adding these ingredients does anything worthwhile for the recreational athlete." And although Gatorade spokesman Patti Jo Sinopoli acknowledges that carbos won't do much for such a person, she contends that "sodium keeps the thirst mechanism active, and water shuts it off." Translation: Sodium-laden drinks will make you feel like drinking more. Bottom line: Unless you're training hard for more than an hour at a stretch, imbibe sports drinks because you actually like their sometimes bitter taste, not because you think you'll hurdle higher, bounce back quicker or, as the ad slogan went, "Be Like Mike."