IGF stands for insulin-like growth factor. Insulin-like growth factor 1 (IGF-1) is a polypeptide protein hormone similar in molecular structure to insulin . It plays an important role in childhood growth and continues to have anabolic effects in adults. It is a natural substance that is produced in the human body and is at its highest natural levels during puberty. During puberty IGF is the most responsible for the natural muscle growth that occurs during these few years. There are many different things that IGF does in the human body. Among the effects the most positive are increased amino acid transport to cells, increased glucose transport, increased protein synthesis, decreased protein degradation, and increased RNA synthesis.