Illustrates role of the MGF C terminal peptide in activating the replication of the mononucleated myoblasts (otherwise termed as satellite cells or muscle progenitor/stem cells). These are the source of the extra nuclei required for local muscle repair. MGF in young normal muscle replenishes the pool of stem cells, and myostatin acts as a negative regulator and pushes then into a quiescent mode. Following the activation of the mononucleated myoblasts to undergo mitosis one of the pair will fuse with the myofiber and switch into myogenic gene expression for the production of contractile such as actin and myosin and other muscle proteins.