Cortisol is naturally created in your body, but you don't want to hold on to all of it. Cortisol at normal levels is helpful in preparing the body to handle stressors and providing athletes with needed sources of energy.

Exercise stresses your body, and without some stress, your muscles would never grow. But too much stress is bad. It increases the production of cortisol-a catabolic stress hormone produced by the adrenal gland-which leads to muscle loss and fat gain.