simple, easily digestible sugars, designed to replenish the muscle glycogen you've depleted with a tough workout. A "protein shake" (which isn't exactly a precise term) is designed to simply give your body a protein boost, and therefore might be appropriate at any time. It may have very few carbohydrates. But when you workout hard, you exhaust your glycogen stores, and glycogen is the primary source of energy for your muscles. Consuming easily digestible carbs soon after your workout replenishes these stores at the time your muscles are most receptive to it, so it's important for helping muscles recover and get stronger.

You don't need anything fancy though. Chocolate milk works just as well as (probably better than) anything Beach Body sells. Some good high-quality protein mixed with some simple sugars helps your muscles recover and get stronger. Or you could just eat a sweet potato or banana with your normal, low-carb protein shake.