A review of 16 major studies found that just thirty minutes a week of strength training is associated with up to a 20 percent reduced risk for dying from any cause, or from cancer, heart disease or diabetes. Adding aerobic exercise reduced risk for dying by 40 percent (British J of Sports Medicine, June 16, 2022;56(13):755-763). The World Health Organization recommends at least two days a week of muscle-strengthening activities for adults because having larger and stronger muscles appears to help prevent many diseases and prolong lives. Not moving your muscles puts you at increased risk for heart failure and premature death (J Am Coll Cardiol, October 2018;72(14)). For example:

• People who exercised less than 30 minutes a day (walking, dancing, gardening) or less than 20 minutes a day of vigorous exercise (running, fast cycling, aerobic exercise) were at 27 percent increased risk for suffering heart and blood vessel problems (European Heart Journal, Nov 8, 2019). Those who increased their levels of activity reduced their risk for heart disease by up to 11 percent.

• Women who averaged walking more than 10,000 steps a day were told to reduce their steps to fewer than 2,000 steps per day and to sit three and a half additional hours each day for two weeks. All the participants had significant rises in blood sugar, reduced response to insulin, raised blood cholesterol, decreased leg muscle size and increased fat in their bellies (Diabetologia, Jun 2018;61(6):1282-1294).

• Diabetic, overweight adults, average age 69, who took 7000 or more steps a day, were asked to take fewer than 1000 steps a day for two weeks (J Gerontol A Biol Sci Med Sci, Jul 9, 2018;73(8):1070-1077). They all had changes predicting loss of muscle size and were less able to respond to insulin, and some had very high rises in blood sugar after meals.

Lack of Exercise Causes Muscle Loss
Stopping exercise, even for a short time, causes a dramatic loss of muscle size and strength. It usually takes at least three times as long to recover the muscle strength that you lost through inactivity (J Am Med Assoc, 2007; 297: 1772-1774).

• Wearing an immobilizing knee brace for just two weeks caused men in their 20s to lose 22-34 percent of their leg muscle strength, and men in their 60s lost 20-26 percent (Journal of Rehabilitation Medicine, June 26, 2015). Six weeks of exercising on a bicycle 3-4 times a week restored leg muscle size and ability to exercise, but did not fully restore muscle leg strength.

• A person loses significant strength after stopping exercise for just four days (Exp Gerontol, 2013; 48: 154-161). The more muscle mass you have, the more you will lose. Young men have about two pounds more muscle weight in each leg than older men do, but after two weeks of inactivity, young men lost 17 ounces of muscle, compared to older men who lost nine ounces. This means that an injury causes fit people with larger muscles to lose muscle size and strength faster than inactive people do. Muscles are made up of thousands of individual fibers like a rope is made of many strands. Regular exercise enlarges fiber size. Inactivity causes muscle fibers to become smaller. Those with the largest fibers lose the most muscle size and strength when they stop exercising.

Rehabilitation After Inactivity
When you use a muscle, you contract the muscle and shorten its fibers. However, you do not contract a muscle fiber equally throughout its length. Muscle fibers are made up of blocks touching end to end to form the long stringy muscle fiber. Each block touches the next block at a point called the Z-line. You have to damage the Z-line to make a muscle grow larger and stronger. If you pedal a bicycle with great pressure, you will damage the muscle fibers at the Z-lines and when they heal, muscles will become stronger. However, most people do not pedal hard or long enough to cause enough damage to make the muscle larger and stronger when it heals. Adding weight training will help you to regain the lost strength and muscle size.

If you have to stop exercising for even a few days, expect to lose strength and endurance. When you resume exercising, you may want to check with your doctor or a personal trainer about doing some form of strength training to regain your lost strength. Caution: Pain at the site of an injury means that you are tearing the previously injured muscle fibers and should stop exercising immediately.

My Recommendations
With aging comes progressive loss of muscle, including heart muscle. Not exercising as you age speeds up this loss of skeletal and heart muscle, to increase risk for heart attacks, heart failure, diabetes, obesity, arthritis, and premature death. Exercise is just one part of an anti-inflammatory lifestyle that is so important for preventing disease and maintaining your quality of life. Other anti-inflammatory lifestyle habits include:
• following an anti-inflammatory diet that includes lots of vegetables, beans, whole grains and other seeds, and restricts sugar-added foods, all sugared drinks, meat from mammals, processed meats and fried foods
• maintaining a healthful weight
• avoiding smoke
• avoiding or restricting alcohol
• keeping blood levels of hydroxy vitamin D above 30 ng/mL