Insulin-like Growth Factor 1 (IGF-1), also known as Somatomedin C, is a peptide related to insulin that helps encourage normal bone and muscle growth and helps decrease blood glucose levels. Bodybuilders have known for years that IGF-1 helps cells to burn fat and increase lean body mass. In fact, this peptide can accelerate weight gain attributed to an increase in muscle mass while keeping the fat off. It can improve energy during a workout and help recovery time after one. So how does this work? IGF-1 has been found to increase in the body after resistance exercise and increase the creation of lean muscle mass.