Muscle injury and repair.

Muscle injury triggers a sequence of events that begin with a host inflammatory response that is followed by muscle fiber regeneration and new collagen synthesis. The inflammatory response involves at least three types of cells, including neutrophils, ED1+ macrophages, and ED2+ macrophages. A host of growth factors and cytokines appear to play a role in the inflammatory process and repair of the damaged tissue. Satellite cells play an integral role in normal development of skeletal muscle by providing a source for postmitotic myonuclei. In addition, the satellite cell is essential to the repair of injured muscle by serving as a source of myoblasts for fiber regeneration. At the same time muscle fiber regeneration is occurring, there is expression of types I and III collagen that under certain circumstances can lead to scarring and fibrosis. Current studies of treatment of muscle injury often incorporate investigations of basic principles of injury and repair together with clinical experience and principles in an effort to coordinate basic science and outcome studies.