Mice with the myostatin gene removed grow more muscle, and researchers have been looking into therapies for muscle wasting based on this mechanism for a number of years. Here is another confirmation that myostatin is involved in age-related changes in muscle mass and strength via its effect on stem cells: "Human aging is accompanied by a progressive loss of muscle mass (sarcopenia). We tested the hypothesis that older males (OMs, 70±4 yr, n=9) would have a blunted myogenic response to a physiological stimulus compared to younger controls (21±3 yr, n=9). Subjects completed an acute bout of intense unilateral muscle loading. Young healthy males matched for body mass and activity level served as the control group. Muscle biopsies and blood were obtained before and at 3, 24, and 48 h after muscle loading. The muscle stem cell response was analyzed ... OMs had 35% fewer basal stem cells and a type II fiber-specific impairment in stem cell content and proliferation. Myogenic determination factor staining and cell cycle analysis illustrated a severely blunted progression through the myogenic program. Myostatin protein and mRNA were 2-fold higher in OMs. Stem cell-specific myostatin levels were not different at baseline; however, there were 67% more myostatin-positive type II-associated stem cells in OMs at 24 h. These data illustrate an age-related impairment of stem cell function in a fiber type-specific manner. The greater colocalization of myostatin with stem cells provides a mechanism for the impaired myogenic capacity of aged muscle."