Your 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 six percent of men are at high risk for breaking their hips or spine with minor falls (CDC/National Center for Health Statistics, August 2015). Just one year of lifting weights can strengthen the bones enough to help protect people from these fractures (Bone, Oct 2015;79:203-212).

Why Bones Weaken with Aging
Bones change all the time. Bone cells called osteoclasts take calcium out of bones and osteoblasts constantly bring calcium back into bones. Exercise increases the rate that osteoblasts bring in calcium to make bones stronger, while inactivity slows osteoblasts to weaken bones. Two hormones, irisin and sclerostin, help signal our bodies to begin the process of breaking down old cells so that new ones can form. Recent research shows that exercise may increase irisin to slow bone loss and prevent osteoporosis in mice susceptible to that condition (Cell, Dec 13, 2018;175(7):1756-1768), so in the future we may have medicines that actually cure osteoporosis.

Bone loss directly parallels loss of muscle. Aging causes you to lose strength, no matter how much you exercise. After age 65, 50 percent of North Americans suffer from loss of muscle that is significant enough to limit their daily activities (J Am Geriatr Soc, 2004;52:80-85). The people who lose the most muscle are usually the ones who die earliest, and they are also most at risk for falls and broken bones. 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). 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).

Exercise Against Resistance to Strengthen Bones
The greater the force on bones, the stronger bones become. Resistance exercise strengthens bones, but only those bones that are stressed by resistance on their specific muscles (Am J of Phys Med & Rehab, 2001;80(1):65-77). Lifting weights in your late 60s, three times a week for just one year, can strengthen bones significantly (Brit J of Sprts Med, 2000;34(1):18-22). A review of 37 studies of men and women over 60 found that a proper exercise program enlarged and strengthened the muscles in 93 percent of the participants (Osteoporosis International, March 1, 2017). In only 14 percent of the participants was there any additional benefit from nutritional changes. It would be best to start a resistance weight program when you are younger because lifting weights during adolescence helps to prevent osteoporosis when you are older (J Ped, 2001;139(4):494-500).

Inflammation Increases Risk for Osteoporosis
Loss of bone and muscle with aging is accelerated by inflammation. Older people who suffer from severe loss of muscle are far more likely to have high levels of the markers of inflammation, measured with blood tests such as CRP, SED rate and adiponectin (Aging Clinical and Experimental Research, August 2017;29(4):745-752). See Inflammation Can Help or Harm

Osteoporosis and sarcopenia of aging are found with other conditions associated with inflammation, including:
• having excess body fat (J Gerontology A Biol Sci Med Sci, 2011;66:888-895; Curr Gerontol Geriatr Res, 2012;2012:216185)
• eating a pro-inflammatory diet that raises blood sugar levels (J Gerontology A Biol Sci Med Sci, Jan 2012;67A(1):74-81)
• being diabetic (Med J Aust, 2016;205(7):329-333)
• having low vitamin D levels (Molecular Aspects of Medicine, Dec 2008;29(6):407-4140)
• not exercising
• having any chronic disease

To make a muscle stronger, you have to exercise that muscle vigorously enough to feel burning in your muscle and damage muscle fibers. Then, when the muscle heals, it is bigger and stronger. Theoretically, damage to any cells in your body turns on your immune system and therefore can cause inflammation, but most studies show that exercise helps to prevent or reduce overall inflammation.

My Recommendations
Since aging weakens your bones and muscles and increases your risk for breaking bones, every person who can do so safely should try to exercise every day. Try to include both activities with continuous motion and exercises against resistance in your program. Continuous endurance exercise such as biking, running, and swimming strengthen primarily your heart, while weight lifting strengthens primarily your skeletal muscles and bones.

If you are not already doing strength-training exercise, first check with your doctor to make sure you do not have any condition that may be harmed by exercise. Then join a gym and ask for instructions on how to use the weight-training machines (Nautilus and similar brands). Used properly, these machines will guide your body to use the correct form and help to prevent injuries as you move weights that match your level of strength. Resistance exercise can increase muscle size and strength in older people (Med Sci Sports Exerc, 2011;43 (2):249-58), but with aging you need to work longer to gain the amount of strength that a younger person would get with the same program (Med Sci Sports Exerc, 2011;43(2):249-58). Since lifting lighter weights many times is less likely to cause injuries, I recommend lifting lighter weights with more repetitions.

• Stop immediately if you feel severe pain or if you have pain that does not go away as soon as you stop lifting the weight. Pain in a muscle or tendon is often the first sign of an impending injury.
• Take the day off if your muscles feel sore or fatigued after a 5-10 minute pre-workout warmup.
• Just using and contracting your muscles in any activity offers health benefits, but you can gain additional benefits by adding intensity with some form of interval training.

In addition to your exercise program, other anti-inflammatory lifestyle habits will also help you to maintain bone strength:
• follow an anti-inflammatory diet
• maintain a healthful weight
• avoid smoke and alcohol
• keep blood levels of hydroxy vitamin D above 20 ng/ml
For more on strengthening bones, see my report on Lifestyle and Drugs to Prevent and Treat Osteoporosis