Adult muscle stem cells possess remarkable regeneration properties and hold great promise in treating degenerative diseases such as muscular dystrophies, healing traumatic injuries and slowing age-related muscle loss. However, when these cells are isolated from the host and propagated in laboratory, they quickly lose their regenerative potency. As a result, they do not efficiently engraft or give rise to new muscle tissues following transplantation procedures. Our laboratory has developed a method to expand human muscle stem cells in culture conditions that retain their regenerative potency. In the past year, we have optimized the conditions so that these muscle stem cells undergo maximal proliferation and maintain high potency in tissue repair in the laboratory. When transplanted into the muscle tissues of a recipient, these cells contribute to the formation of new muscle fibers better than freshly isolated stem cells. Thorough characterization of these propagated cells suggests that they are suitable to be used in stem cell-based treatments of diseases and conditions of muscle degeneration.