From a physiological perspective, muscle and their fibers are made of protein. These fibers increase in size when protein is synthesized. A bout of physical activity increases the breakdown in muscle protein and at the same time lowers protein creation.
There is also a depletion of glycogen, which is the primary energy source for muscles. Finally, levels of insulin drop during physical activity. Insulin is the a hormone responsible for enabling tissues to absorb glucose, to build glycogen, and amino acids used to build muscle protein, while decreasing the breakdown of muscle protein during the post-exercise period.
The goal of post-exercise nutrition is to replenish glycogen levels that will lead to the process of protein synthesis (creation). Carbohydrates such as those found in the P90X Recovery Formula are the body’s primary source of glucose, a fundamental ingredient in the production of glycogen.