When mechanical overload is introduced to a muscle (as by weight training), the IGF-1 gene released and is differentially spliced during the bodies response. Initially, it it is spliced to produce predominantly IGF-1Ec (called the MGF splice variant of IGF-1). This early splicing stimulates satellite cells into activation. Which in turn allows the activation of extra undamaged nuclei to grow new muscle fiber and tissue. The appearance of MGF also initiates the upregulation of new protein synthesis. After this initial splicing of IGF-1 into MGF, production then switches towards producing a systemic release of IGF- 1Ea from the liver, which also upregulates protein synthesis as well. The expression of IGF-1 splice variants, over the course of the healing and regrowth phase of muscle repair is thought to be the primary anabolic mechanism by which the body produces new muscle. MGF is available as an injectable peptide.