Creatine is a substance naturally found within muscle cells which, while not an amino acid itself, has many similarities with amino acids and is produced from glycine and arginine. About half of an average person’s creatine is synthesized by the liver in this way, while the rest is obtained through diet with red meat and seafood being especially rich sources. Most of the body’s creatine is found in muscle tissue, but some is present in the brain as well. Creatine is extremely popular as a supplement among athletes and bodybuilders for its ability to support additional strength and power output during resistance training, but research has also shown it to support both physical and mental endurance under conditions of high exertion.