We've all seen the commercials: Bulked-up jocks slam down a bright blue sports drink, then drive to the hoop or race across the finish line. The unstated but unmistakable message is that you, too, can become a super athlete by drinking this product.

Do sports drinks really boost athletic performance, or are such claims just marketing hype? The answer is complex.

Sports drinks are designed primarily to quickly replace water lost during strenuous activity. Water makes up about 60 percent of the body and 80 percent of the muscles. Water helps regulate body temperature through sweating and plays a key role in transporting oxygen and nutrients through the body. Water also is vital to moving waste from the body.

People generally feel thirsty after losing just 1 percent of their body weight through sweat. If water loss reaches 2 to 4 percent, performance may be affected as symptoms of dehydration set in. Sports drinks can help prevent this dehydration.

Old-fashioned alternative

However, before you start digging for change at the gym vending machine, think about this: Good, old-fashioned, free tap water is just as effective as the average sports drink at replacing most types of fluid loss.

Most people work out at a moderate pace for 60 minutes or less per session. Water does a great job of restoring fluids following workouts of this intensity. Water quickly moves from the stomach to the bloodstream and rehydrates the body without contributing unnecessary calories.