As you might imagine, exercise affects the behavior of muscle stem cells: "researchers determined that an adult stem cell present in muscle is responsive to exercise, a discovery that may provide a link between exercise and muscle health. The findings could lead to new therapeutic techniques using these cells to rehabilitate injured muscle and prevent or restore muscle loss with age. Mesenchymal stem cells (MSCs) in skeletal muscle have been known to be important for muscle repair. ... Since exercise can induce some injury as part of the remodeling process following mechanical strain, we wondered if MSC accumulation was a natural response to exercise and whether these cells contributed to the beneficial regeneration and growth process that occurs post-exercise. ... The researchers found that MSCs in muscle are very responsive to mechanical strain. They witnessed MSC accumulation in muscle of mice after vigorous exercise. Then, they determined that although MSCs don't directly contribute to building new muscle fibers, they release growth factors that spur other cells in muscle to fuse and generate new muscle, providing the cellular basis for enhanced muscle health following exercise. ... Next, the group hopes to determine whether these cells contribute to the decline in muscle mass over a person's lifetime. Preliminary data suggest MSCs become deficient in muscle with age. The team hopes to develop a combinatorial therapy that utilizes molecular and stem-cell-based strategies to prevent age-related muscle loss."