When you read about people dying of “natural causes,” it usually means that they died of heart failure because they spent too much time lying in bed. When you become inactive, you lose your skeletal muscles at an alarming rate, and losing skeletal muscle causes loss of heart muscle until your heart can become too weak to pump blood to your brain and you die.

In 1914, Dr. Ernest Starling described what is today known as Starling’s Law, that strengthening skeletal muscles strengthens heart muscle and not the other way around (Circulation, 2002;106(23):2986-2992). When you contract your skeletal muscles, they squeeze the veins near them to pump extra blood back to your heart. The extra blood flowing back to your heart fills up your heart, which stretches your heart muscle, causing the heart muscle to contract with greater force and pump more blood back your body. This explains why your heart beats faster and harder to pump more blood when you exercise. The harder your heart muscle has to contract regularly in an exercise program, the greater the gain in heart muscle strength.

Inactivity Damages Brain and Nerve Cells
Preventing mice from using their hind limbs for just 28 days interfered with normal function of mitochondria in cells so that blood levels of oxygen dropped, preventing the sub-ventricular zone of the brain from maintaining normal nerve function and making new nerves (Frontiers in Neuroscience, May 23, 2018). Many studies show that physical activity is necessary for the healthy growth of new nerves during a human lifetime (J Neurosci Res, 2016;94:310–317). On the basis of these and many other studies, this means that not using your legs and arms causes loss of nerves, which causes loss of muscles (particularly heart muscle), that can eventually lead to heart failure and death.
• The larger your skeletal muscles, the stronger your heart and the lower your chance of suffering heart attacks and heart disease (J Epidem & Comm Health, Nov 11, 2019).
• The less you exercise, the weaker your heart and the more likely you are to become diabetic (Diabetes Care, 2002; 25:1612–1618).
• The larger your muscles, the less likely you are to die of heart diseases (Am J of Cardiology, Apr 15, 2016;117(8):1355-1360).
• A study of almost a million adults with no history of heart disease followed for 10 years found that those who did not exercise were at 65 percent increased risk for strokes and heart attacks, the same rate as that found for smoking (Euro J of Prev Cardiology, Feb 10, 2020).
• A study of 900 heart failure patients found that those who did not exercise were twice as likely to die within three years (Am J Cardiol, 2016 Apr 1; 117(7): 1135–1143).
• A study of 51,451 participants, followed for 12.5 years, found a strong association between exercise and decreased risk for heart failure (J Amer Col of Cardiol, Mar 2017;69(9)).
• A study of 378 older adults showed that the smaller the muscles in their arms, legs and trunk, the smaller and weaker the upper and lower chambers of their hearts (J Am Geriatr Soc, Dec 2019;67:2568-2573).
• Low skeletal muscle size predicted death in people who had chronic heart failure (Cardiology, March 25, 2019).

Severe Loss of Muscle with Aging is Common
Between 25 and 50 percent of North Americans over the age of 65 suffer from severe loss of skeletal muscle (sarcopenia) that is significant enough to limit their daily activities (J Am Geriatr Soc, 2004;52:80–85). A regular exercise program is the best way to slow down this loss of strength and coordination, but even if you exercise regularly, you will still lose muscle as you age (Aging Male, September-December 2005). After age 40, people lose more than eight percent of their muscle size per decade and by age 70, the rate of muscle loss nearly doubles to 15 percent per decade, markedly increasing risk for disability and disease (Am J Epidemiol, 1998;147(8):755–763; Nutr Rev, May 2003;61(5 Pt 1):157-67).

The people who lose the most skeletal muscle are usually the ones who die earliest. They are also most at risk for falls and broken bones. Muscles are made up of hundreds of thousands of individual fibers, just as a rope is made up of many strands. Each muscle fiber is innervated by a single motor nerve. With aging you lose motor nerves, and with each loss of a nerve, you also lose the corresponding muscle fiber that it innervates. For example, the vastus medialis muscle in the front of your thigh contains about 800,000 muscle fibers when you are 20, but by age 60, it probably has only about 250,000 fibers. However, after a muscle fiber loses its primary nerve, other nerves covering other fibers can move over to stimulate that fiber in addition to stimulating their own primary muscle fibers. A regular exercise program can help to slow the loss of muscle fibers and improve mobility (Physiol Rev, Jan 1, 2019;99(1):427-511). Lifelong competitive athletes over 50 who train four to five times per week did not lose as many of the nerves that innervate muscles and therefore retained more muscle size and strength with aging than their non-athlete peers (The Physician and Sportsmedicine, October 2011;39(3):172-8). Lifelong competitive runners over 60 can have almost the same number of muscle fibers as 25-year-olds.

Researchers reviewed eight studies using accelerometers to follow 36,383 adults, 40 years of age and older, for six years and found that exercising regularly in adulthood, regardless of intensity, is associated with reduced risk for early death, while sitting for more than nine hours a day is associated with increased risk for premature death (Brit Med J, August 21, 2019). The death rate dropped progressively as light physical activity increased up to five hours per day and moderate activity increased up to 24 minutes per day. Examples of:
• light intensity included walking slowly, cooking and washing dishes;
• moderate activity included brisk walking, vacuuming or mowing the lawn; and
• vigorous activity included jogging or carrying heavy loads.
Lack of physical activity doubled a person’s chances of suffering a heart attack, while a regular exercise program helps prevent it (Eur Heart J, January 15, 2019).

Preventing Muscle Loss
Resistance exercise increases muscle size and strength in older people, 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). Competitive masters athletes, 40 to 80 years old, who train four to five times per week, lose far less muscle size or strength than their non-exercising peers (The Physician and Sportsmedicine, October 2011;39(3):172-8). Eighty-year-old men who still compete in sports have been found to have more muscle fibers than inactive younger men (Journal of Applied Physiology, March 24, 2016). Inactivity causes rapid loss of muscle size and strength. 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). Prolonged periods of inactivity due to bed rest, injured nerves, casting or even decreasing the force of gravity (in astronauts) causes loss of muscle tissue which leads to insulin resistance, higher blood sugar levels and increased risk for diabetes (Med Hypotheses, 2007;69(2):310-21).

My Recommendations
A key to prolonging your life and preventing disease is to keep on moving. Lying in bed for many hours each day is a certain way eventually to kill yourself. Each day that you spend not moving your muscles weakens your heart until eventually you can die of heart failure.
• Exercise will prolong your life, but you do not have to have a specific exercise program. You just need to keep on moving for a large part of each day. It is harmful just to sit or lie down all day long. It is healthful to mow your lawn, wash your dishes, make your bed, vacuum your house, go for a walk, and participate with your friends in activities in which you are moving your arms and legs — dancing, cycling, swimming, running, nature walks and so forth.
• To gain maximum health benefits from your skeletal muscles, you should include some sort of resistance exercise. 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. Caution: Exercise can cause a heart attack in a person who has blocked arteries or heart damage.

Then join a gym and ask for instructions on how to use the weight-training machines. Since lifting heavier weights is far more likely to injure you than lifting lighter weights, I recommend that you lift lighter weights with far more repetitions. Older people, in particular, can use each specific weight machine and lift and lower a lighter weight up to 100 times in a row. Stop that exercise when the muscles start to feel tight or hurt.

Checked 11/23/20