Athletes are taught to refuel with protein immediately after a workout. Most opt for a quick hit with an easy, portable protein shake. But just drinking protein won't replenish muscle glycogen stores. (See Get the Most Out of Your Post-Workout Protein.) After an intense workout, the body has basically depleted all of its glycogen, which is the primary fuel used for energy production. In order to get the most out of your workouts and to achieve peak performance, restoring glycogen immediately after a workout is extremely important. It's one of the reasons energy levels decrease when carbohydrate intake is reduced.
Bottom line: you need to consume something that contains both protein and carbohydrates.
That's why the only post-workout drink I'd recommend to an athlete—high school, college or professional—is low-fat chocolate milk. After a workout, your muscles are like a sponge ready to soak up whatever you feed them. One cup of low-fat chocolate milk is fortified with 30% of your daily recommended calcium, 25% of your daily recommended vitamin D, and phosphorus. Plus, it's a good source of vitamin A and C. With 26 grams of carbohydrates and eight grams of high-quality protein, a single serving of chocolate milk is the perfect blend of what your body needs after a strenuous workout to replenish your glycogen stores and repair damaged muscle tissue.
You can purchase chocolate milk almost anywhere. For maximum results, I recommend drinking a pint of low-fat chocolate milk after your workout. It can also be used as a healthy afternoon snack to keep you energized throughout the day.