Everyone should try to keep on moving their muscles every day. Sitting around for long periods of time can cause you to become diabetic and increase your risk for a heart attack, and lying in bed for long periods puts you at increased risk for heart failure and premature death (J Am Coll Cardiol, October 2018;72(14)).
• 518 postmenopausal overweight women, average age 63, wore accelerometers on their hips for 14 days to track how much they were moving each day. Women who sat longer had higher blood insulin levels because inactivity prevents your body from responding to insulin, so your pancreas releases even more insulin to overcome this (J Amer Heart Assoc, Feb 17, 2020). High levels of insulin are an early sign of diabetes because diabetes is often caused by inability to respond to insulin, so insulin levels rise. For each additional hour the women sat each day, they had a six percent increase in insulin and a seven percent increase in insulin resistance. Extended sitting time was also associated with higher levels of body fat, a wider waist and higher triglyceride levels. See Inactivity Increases Risk for Diabetes
• Researchers at the University of Liverpool in England asked 45 healthy active adult men and women who averaged walking more than 10,000 steps a day, 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 (Diabetologia, Jun 2018;61(6):1282-1294). All of the participants had significant rises in blood sugar, lowered response to insulin, raised blood cholesterol, decreased leg muscle size and increased fat in their bellies.
• 22 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. In most of the subjects, markers of diabetes (sugar tolerance and insulin responses) remained abnormal two weeks after they had resumed their normal activity levels.

Inactivity Increases Risk for Heart Failure
People who lie in bed day after day suffer progressive weakening of their heart muscle. Eventually the heart becomes too weak to pump enough oxygen to the brain, they stop breathing and die from heart failure. A study on mice shows how this is likely to happen. 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). The study showed that preventing mice from using their legs:
• decreased the number of neural stem cells that become nerves by 70 percent, compared to normally exercising mice, and
• prevented precursors to nerves and their insulation cells from becoming fully mature cells.

With aging, you lose nerves and new nerves cells take their place. This study shows that lack of exercise slows down the growth of new nerves. With the loss of nerves comes loss of the muscle fiber innervated by that nerve, so lack of activity causes a progressive weakening of both skeletal and heart muscles. This may explain how inactivity can eventually cause heart failure and kill you, and why diseases that damage nerves that move muscles, such as multiple sclerosis or spinal muscular atrophy, have such high rates of death from heart failure. Many studies on humans have demonstrated that exercise protects your heart:
• Of 1,119,925 people, average age 67, those who exercised less than 30 minutes a day (brisk 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, and those who changed from being inactive to becoming moderately or vigorously active three to four times a week were at reduced risk for heart diseases. Disabled people who increased their exercise programs reduced risk for heart disease by 16 percent, and those with diabetes, hypertension, or high blood cholesterol levels who increased their exercise programs reduced their risk for heart disease by 4-7 percent.
• 28,982 patients in heart failure, average age 75.7, received an implanted heart rate monitor and defibrillator, and were followed for five years. Patients were four times more likely to be hospitalized or die within two weeks after they reduced moving about by a half hour a day, or reduced their physical activity by as little as 10 minutes a day (J of the Amer Coll of Card, February 5, 2020).
• Researchers followed 21,758 healthy men over 51 years of age for more than 10 years. Those who exercised regularly long and hard (>3000 MET-min/week) had higher heart calcium scores, showing that they had higher levels of calcium in the arteries leading to their hearts (JAMA Cardiol, Feb 1, 2019;4(2):174-181). High levels of calcium in arteries signify that the plaques are stable and far less likely to cause heart attacks. Heart attacks are not caused by narrowed arteries. They are caused by plaques breaking off from arteries, causing clots to completely block blood flow through an artery. Vigorous exercisers have plaques stabilized by extra calcium that helps to prevent plaques from breaking off, so vigorous exercisers are far less likely to suffer heart attacks than those who do not exercise.

Inactivity Causes Muscle Loss
A study from the University of Copenhagen showed that 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. This study shows that:
• As soon as you stop moving, your muscles begin to weaken.
• The larger your muscles, the more muscle you have to lose.
• The younger and stronger you are, the faster you lose strength.
Other studies show that it takes three times the amount of time you were inactive to regain the muscle that you have lost, probably because you are inactive for the whole day and you exercise only a short time each day.

Inactivity Linked to Arthritis
People with arthritis should keep on moving, because inactivity worsens arthritis by preventing joints from healing. The majority of people with arthritis are inactive and are often overweight, diabetic or pre-diabetic. The CDC Morbidity and Mortality Weekly Report (November 9, 2018; 67(44);1238–1241) found that 32 percent of adults with arthritis have pre-diabetes or diabetes, 56.5 percent are physically inactive and 50.1 percent are obese.

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, nuts, 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 20 ng/mL