Creatine is a naturally occurring compound in muscle tissue and functions as an energy reservoir to maintain optimal levels of ATP production during intense exercise Creatine may be especially useful for those doing short-term, intense (anaerobic) exercise. Creatine (creatine monohydrate) is used in muscle tissue for the production of phosphocreatine, an important factor in the formation of ATP, the source of energy for muscle contraction and many other functions in the body. Creatine monohydrate supplementation increases phosphocreatine levels in muscle in most people, especially when accompanied by exercise or carbohydrate intake.