To preserve muscle and bone size and strength, recreational runners and cyclists are recommended to do upper body and core weight lifting or resistance training. Bodies lose muscle and bone size and strength with aging. Bones weaken progressively after age 30, and between ages 35 and 50, about 28 percent of North American men and women suffer from bone weakening called osteopenia (J Amer Osteo Assoc, June 2019;119:357-363). By age 65, 25 percent of women and 6 percent of men are at high risk for breaking their hips or spine with minor falls (CDC/National Center for Health Statistics, Aug. 2015).
The people who lose the most muscle are usually the ones who are most at risk for falls and broken bones. Any prolonged period of inactivity, such as bed rest, injured nerves, wearing a cast or even living in a decreased force of gravity, will cause loss of muscle tissue (Med Hypotheses, 2007;69(2):310-21). If you inactivate a leg by putting it in a cast, you lose a significant amount of muscle size in just four days (Nutrition, Acta Physiol (Oxf), March 2014;210(3):628-41). Just one year of lifting weights can strengthen the bones enough to help protect people from fractures (Bone, Oct. 2015;79:203-212).
