The primary function of carbohydrates is to provide energy for the body, especially the brain and the nervous system. An enzyme called amylase helps break down carbohydrates into glucose (blood sugar), which is used for energy by the body. Carbohydrates are classified as simple or complex. The classification depends on the chemical structure of the food, and how quickly the sugar is digested and absorbed. Simple carbohydrates have one (single) or two (double) sugars. Complex carbohydrates have three or more sugars.
The most critical nutritional period for muscle growth is the post-workout meal. Following a hard workout, your body is severely depleted of glycogen and glucose. Hard working muscles utilize glucose (usable form) and glycogen (stored form) for energy. The amount of fuel in your tank obviously does not last forever. As such, there is a point at which blood glucose levels (available energy) and glycogen levels (stored energy) get so low that effective exercise cannot occur. This is typically characterized by a decline in energy levels. There simply isn’t enough available energy for working tissues to use. This is the main reason why you need to eat an adequate amount of carbs post-workout in order to maximize this window of opportunity and replenish your glycogen stores.