Creatine is a chemical made naturally in the body from amino acids readily obtained from meat and fish. Inside the body, creatine or creatine supplements are involved in energy expenditure during bodybuilding, workout or exercise. Much of it is phosphorylated (i.e. a phosphate group is added to it) to form phosphocreatine, an energy-rich compound used by the muscles during very short bursts of explosive activity.  Read more on Creatine