Fitness and recovery from illness

Exercise is one of the most important things you can do to improve your health. Among other health and fitness benefits, it can have a positive effect on your immune system. People who participate in moderate exercise daily have fewer and less severe colds and have up to 50% fewer sick days than those who aren’t regularly active.

Research shows that exercise increases the activity of certain immune cells called helper T cells. This makes the immune system response to viruses, like the cold, flu, and coronavirus, more robust. The strongest evidence is seen when the exercise is moderate in intensity and duration, such as walking, jogging, cycling, or swimming for 30–60 minutes.

Improving your fitness through regular exercise is also important for recovering from illness that keeps you from being active for several days or a hospitalization that keeps you in bed for a week, a month, or longer.

This is the topic of my Health & Fitness column in the Aiken Standard this week.

Patient walking in hospital


The problem with periods of inactivity, like bed rest or hospitalization, is that there are severe physiological effects that occur within days and get worse over time. You may have noticed this as weakness and fatigue after spending a few days in bed with a cold.

Muscle strength declines with each day of bed rest, and can be 50% lower following as little as three weeks. That reduction in strength could limit a person who was already deconditioned to a point where he or she would have difficulty completing the most basic activities of daily living.

A person who was fit and strong when they went into the hospital would certainly be better off when released. And older adults fare worse than younger individuals. According to one study, the decline in strength seen in older men in just 10 days was equivalent to the change measured after 28 days in men 30 years younger.

It’s not just the muscles that are affected, the bones get weaker, too. In fact, 12 weeks of bed rest can reduce bone density by as much as 50%, exposing patients to a greater risk of fracture. This is due to the reduced stress on the bone from not standing and walking as well as the lack of muscle activity.

Two of the most effective ways to build bone density are putting stress on bones through weight-bearing activity and the action of the muscles pulling on the bones from resistance training. Because bed rest eliminates both of these stresses, bone density declines rapidly.

One unique study from the 1960s had healthy young men complete three weeks of bed rest. They all experienced a rapid decline (over 20%) in their aerobic fitness, but recovered quickly after the experiment ended. These individuals also had their fitness tested again 30 years later. It turns out that the decline in fitness in those young men in three weeks of bed rest was greater than the decline in fitness that occurred over 30 years of aging!

The good news is that most patients are encouraged to move around as much as possible. Some receive inpatient physical therapy or rehab to help lessen the effects of prolonged bed rest. It is important to take advantage of these opportunities if you, or a loved one, are hospitalized. Since the effects of bed rest are seen in people of all ages, everyone can benefit from building a foundation of good fitness through regular exercise.


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