Creatine is a nitrogen-containing compound and exists in the foods, typically meat and fish. Creatine can also be formed in the body from the amino acids glycine, arginine, and methionine. Creatine plays a key role in the phosphagen energy system, and is the primary source of ATP (the main energy substrate in our body) during short-term, high-intensity activities. Creatine exists as both free form creatine and phosphocreatine in the body. The body produces about 1g creatine daily. Creatine monohydrate is one of the most popular supplements used by people looking to build lean muscle mass, maximize performance, and increase strength. According to survey data, over 40% of National Collegiate Athletic Association (NCAA) athletes reported that they have used creatine.