The exact cause of muscular atrophy is unknown , but it may be due to the gradual failure in the `` satellite cells '' which help to regenerate skeletal muscle fibers , and a decrease in sensitivity to or the availability of secreted growth factors which are necessary to maintain muscle mass and satellite cell survival . The exact cause of sarcopenia is unknown , but it may be due to a combination of the gradual failure in the `` satellite cells '' which help to regenerate skeletal muscle fibers , and a decrease in sensitivity to or the availability of critical secreted growth factors which are necessary to maintain muscle mass and satellite cell survival .