Skeletal muscle satellite cell characteristics in young and older men and women after heavy resistance strength training.

Skeletal muscle satellite cell proportions and morphology were assessed in healthy, sedentary young and older men and women in response to heavy resistance strength training (HRST). Fourteen young (20-30 years) men (n = 7) and women (n = 7) and 15 older (65-75 years) men (n = 8) and women (n = 7) completed 9 weeks of unilateral knee extension exercise training 3 days per week. Muscle biopsies were obtained from each vastus lateralis before and after training, with the nondominant leg serving as an untrained control. All four groups demonstrated a significant increase in satellite cell proportion in response to HRST (2.3 +/- 0.4% vs 3.1 +/- 0.4% for all subjects combined, before and after training, respectively; p < .05), with older women demonstrating the greatest increase (p < .05). Morphology data indicated a significant increase in the proportion of active satellite cells in after-training muscle samples compared with before-training samples and with control leg samples (31% vs 6% and 7%, respectively; p < .05). The present results indicate that the proportion of satellite cells is increased after HRST in young and older men and women, with an exaggerated response in older women. Furthermore, the proportion of satellite cells that appear morphologically active is increased as a result of HRST.