Satellite cells are stem cells positioned under the basal lamina of muscle fibers that can give rise to differentiated myogenic cells, or, alternatively, maintain their stemness via a self-renewal mechanism. Satellite cells play a key role in the routine maintenance, hypertrophy, and repair of damaged adult skeletal muscles. After activation, PAX7+ MYOD+ satellite cells actively proliferate, and fuse with existing myofibers following activation of the myogenin differentiating gene. A small proportion of the cells will return to an undifferentiated PAX7+ stage and repopulate the satellite cell niche.