Creatine is the number one supplement for improving performance in the gym. It is the single most studied and tested ingredient/supplement which shows an increase in muscle mass, strength, and improved exercise performance. Creatine is found naturally in muscle cells. It helps your muscles produce energy during lifting or exercise. About 95% of your body's natural creatine is stored in muscles in the form of phosphocreatine. The other 5% is found in your brain, kidneys, and liver. When supplementing with creatine, you increase your stores of phosphocreatine. This is a form of stored energy in the cells, as it helps your body produce more of a high-energy molecule called ATP. ATP is often called the body's energy currency. When you have more ATP, your body can perform better during exercise (it helps your muscles produce energy during lifting or exercise). Creatine also alters several cellular processes that lead to increased muscle mass, strength, and recovery.