Insulin-like growth factor is a highly anabolic hormone that is released in the liver as well as in the peripheral tissues in response to the GH so that a new muscle could be built. The main work of IGF-1 is to build new muscle tissues by promoting nitrogen retention and protein synthesis. It differs from original IGF-1 in that it possesses an arginine instead of a glutamic acid and also has an additional 13 amino acids. As a result, it is approximately three times more potent than IGF-1 and possesses a significantly longer half-life of about 20– 30 hours (comparative to IGF-1’s half-life of about 12–15 hours).