A study of 1,275 men and women found that those who had very weak handgrip strength had signs of accelerated aging, as measured by deterioration of the DNA in their cells (J Cachexia Sarcopenia Muscle, Nov 9, 2022). Previous studies have shown these DNA tests:
• are dependable measures of biological aging (Clin Epigenetics, 2020 Oct 15;12(1):148)
• are associated with significantly increased risk for certain cancers, particularly colon cancer (Elife, Mar 29, 2022;11:e75374)
• predict increased risk for becoming diabetic (Sports Med, 2016;46:619-628; Age Ageing 2018;47:685-691)
• predict increased risk for chronic lung disease, lung cancer, diabetes, blocked arteries leading to heart attacks and ischemic heart disease (Clin Epigenet, July 31, 2020;12(1):115)

The authors of this study cited earlier studies showing that grip strength appears to be a better predictor of life expectancy than blood pressure. Many other studies show that having weak muscles is associated with a host of diseases and premature death. Muscle weakness predicts increased risk for:
• physical disability in older people (J Nutr Health Aging, 2018;22:501-507; Ethn Health 2017;26:1-12)
• long-term disability and development of chronic diseases (Exp Gerontol, 2021;152:111462)
• dementia (Clinical Interventions in Aging, July 5, 2018;13)
• cancer (Cancer Med, Jan 2022;11(2):308-316)
• heart attacks (J of Epidem & Comm Health, Nov 11, 2020;74(1):26-31)
• premature death (J Am Med Dir Assoc, May 2020;21(5):621-626.e2)

Muscles Weaken with Aging
You can expect to lose muscle size and strength as you age. Between 40 and 50 years of age, the average person loses more than eight percent of their muscle size. This loss increases to 15 percent per decade after age 75. The people who lose the most muscle usually are the least active, exercise the least and are the ones who die earliest. Older people who lose the most muscle are four times more likely be disabled, have difficulty walking, and need walkers and other mechanical devices to help them walk (Am J Epidemiol, 1998; 147(8):755-763).

Your muscles are made up of thousands of muscle fibers, just as a rope is made up of many strands. Every muscle fiber is innervated by a single nerve fiber. With aging you lose nerves, and when you lose a nerve attached to a muscle fiber, that muscle fiber is lost also. A 20-year-old person may have 800,000 muscle fibers in the muscle in the front of his upper leg, but by age 60, that muscle would have only about 250,000 fibers. For a 60-year-old to have the same strength as a 20-year-old, the average muscle fiber needs to be three times as strong as the 20-year-old’s muscle fibers. You cannot stop this loss of the number of muscle fibers with aging, but you can enlarge each remaining muscle fiber and slow down the loss of strength by exercising muscles against progressive resistance (Experimental Gerontology, August 13, 2013).

My Recommendations
I believe that everyone who is able should do some form of resistance exercises to increase their muscle size and strength for as long as they can. 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. If you are not comfortable with going to a gym, consider setting up a resistance exercise program at home. See Resistance Exercise You Can Do at Home. I recommend that you hire a knowledgeable personal trainer at least for a few sessions to set up your home program and help with choices of equipment. I also recommend lifting light weights with more repetitions, because lifting lighter weights many times is less likely to cause injuries than lifting heavier weights a few times. See Making Muscles Stronger