THE CALORIE QUESTION
To provide actual bona fide energy, a drink has to contain calories, and that usually means sugar. If you're concerned about calories—and if that's one reason you're on the treadmill at the gym in the first place—read the labels.
First, check serving size. Some beverages have 2 to 3 servings per bottle or can, so if your drink is not calorie-free, serving size is important. Calories in energy drinks most often come from sugar: 4 calories per gram. A 12-ounce Coke, for reference, has 140 calories.
Second, ask if these are the right kind of calories. The body perceives calories delivered in liquid form as less physiologically satisfying than those found in solid foods. It may be better to drink a noncaloric drink and eat a fiber-rich energy bar.