Skeletal muscle satellite cells (SCs) have been shown to be instrumental in the muscle adaptive response to exercise. The present study determines age-related differences in SC content and activation status following a single bout of exercise. Ten young (22 +/- 1 years) and 10 elderly (73 +/- 1 years) men performed a single bout of resistance-type exercise. Muscle biopsies were collected before and 12, 24, 48, and 72 h after exercise. SC content and activation status were assessed in type I and type II muscle fibers by immunohistochemistry. Myostatin and MyoD protein and messenger RNA (mRNA) expression were determined by Western blotting and rtPCR, respectively. In response to exercise, it took 48 h (young) and 72 h (elderly) for type II muscle fiber SC content to exceed baseline values (P < 0.01). The number of myostatin + SC in type I and II muscle fibers was significantly reduced after 12, 24, and 48 h of post-exercise recovery in both groups (P < 0.01), with a greater reduction observed at 24 and 48 h in the young compared with that in the elderly men (P < 0.01). In conclusion, the increase in type II muscle fiber SC content during post-exercise recovery is delayed with aging and is accompanied by a blunted SC activation response.