In a study published in The International Journal of Sport Nutrition and Exercise Metabolism, subjects given chocolate milk before hopping on the stationary bikes were able to ride 49 percent longer than subjects given a generic carbohydrate-replacement beverage. And on top of that, they pedaled even harder. Total work performed by the chocolate-milk group was greater than the work performed by subjects drinking carbohydrate-replacement drinks or electrolyte-fortified sports drinks.
The reason? Milk has naturally occurring electrolytes that keep you hydrated—more hydrated then water. Its natural sweetness helps push more energy into your muscles. Another study from 2009 found similar results, but it went one step further by asking participants which beverage they thought tasted better. Not surprisingly, 100% chose chocolate milk.