Muscular dystrophies are characterized by progressive degeneration with regeneration trying to keep up. As there is no cure for muscular dystrophy, it is important to understand the extent of repair in the muscles and if parts of the repair mechanism are affected by the primary disease. In many cases looking regeneration may also offer clues to the extent of the original degeneration. We have studied regeneration in a number of muscular dystrophies and myopathies and found that later stages of regeneration appears to require calpain-3, that up to 40% of muscle fibers can be undergoing active regeneration at any one time and that there likely is a limit to the regenerative mechanism. In order to develop an effective way of activating and boosting the regeneration, we have found in animal models that growth factor activation of muscle stem cells considerably increases muscle mass and that the limiting factor to regeneration in patients with muscular dystrophy likely is myostatin. We are currently utilizing this knowledge in a new enhanced therapy for boosting muscle regeneration.