By Deborah Westergaard, MD | Pain Experts | Dallas–Plano Muscle Mass Longevity is Important and Why Muscle Mass Declines With Age In sedentary adults, muscle mass typically falls about 1–2% per year starting in midlife, and this loss may accelerate after age 60. Resistance training can substantially slow this decline. Why it matters: less muscle means poorer joint stability, lower metabolism, and higher risks of imbalance, falls, and fractures. Add to that the stress of overu