I want a better explanation, though. They say that your muscles operate (not grow) off of stored glycogen. They say that when the glycogen runs out (e.g. when a marathoner "bonks"), they need to be refueled with carbs.

Now this is confusing to me, because Taubes says your body only burns carbs for a short time after you eat, then you go back to lipolysis right away and your whole body is burning lipids. So if this is true, why can't your muscles burn lipids for energy?