By Michael Ormsbee, Ph.D., Florida State University

Edited by Kate Findley, The Great Courses Daily

Is it possible to exercise too much? Michael Ormsbee, Ph.D., explains how excessive exercise can cause cellular damage, leading to conditions such as cancer and diabetes. But if you think this gives you a pass to be a couch potato, think again—inactivity is just as bad.

How Excess Exercise Impacts Cellular Health

While the food you eat plays a significant role in your health, exercise can also impact your cellular health and function. In fact, excessive exercise can actually cause cellular damage. 

This seems counterintuitive, since conventional wisdom states that exercise is good for us, but it’s true. Exercise naturally increases the production of free radicals, which are molecules that have an unpaired electron in their outer shell. This missing electron in these molecules causes them to be unstable and highly reactive.

To regain stability, the free radical molecule steals electrons from healthy cells in your body. When this happens, the free radical leaves the healthy cell damaged and unable to perform its usual functions. 

This free radical damage doesn’t stop with just one cell. Once one free radical attack occurs, it sets off a domino effect, and the newly damaged cell moves on to other healthy cells as they attempt to become neutral again.

A single chain reaction can lead to thousands of damaged cells just from one bout of intense exercise. Excessive free radical damage has been associated with accelerated aging, cancer, diabetes, and coronary artery disease.

When Exercise Becomes Problematic

“Now, don’t let this scare you too much, and don’t stop exercising because these potential free radical attacks might occur, because, luckily, our bodies have the ability to fight free radical attacks by forming three natural antioxidants known as glutathione, catalase, and superoxide dismutase,” Professor Ormsbee said.

“These substances donate extra electrons to free radicals and prevent them from damaging healthy cells. The major problem with exercise occurs when it’s too extreme, causing the production of free radicals to exceed the body’s ability to produce antioxidants.”

For example, a study conducted at Hebrew University in Israel in conjunction with the National Institutes of Health in Maryland investigated this exercise-induced oxidative stress. Thirty-one men completed a six-month, five-day-per-week training schedule that involved two very extreme 30- and 50-mile marches while carrying an extra 77 pounds—or 35 kilograms—of weight. 

Not surprisingly, after these long marches, the men experienced oxidative damage, causing significant cellular damage. The researchers also found a significant increase in liver enzymes, indicating more work being done by the liver, which may also suffer injury as a result.

“This study was in men, but my lab has also seen excessive cell damage in ultra-endurance athletes of both sexes,” Professor Ormsbee said.

Cellular Damage and Inactivity

Fortunately, your diet can help ward off this exercise-induced oxidative stress. Your diet should include lots of fruits and vegetables that are full of antioxidants such as vitamin C, vitamin E, vitamin A, and selenium. A great newly researched post-exercise supplement to reduce oxidative stress is tart cherry juice—it’s loaded with antioxidants.

Keep in mind that being still and sedentary can also have a negative impact on cellular health and integrity. Many experts agree that sedentary lifestyles are associated with increased cardiovascular disease, atherosclerosis, obesity, diabetes, accelerated aging, and more. 

Once again, oxidative stress plays a major role in these dysfunctions. Researchers from Germany compared the effects of physical inactivity, or doing nothing, with voluntary running in mice. 

After six weeks of remaining completely inactive and doing no physical activity, there was a significant increase in markers of cellular damage, vascular dysfunction, and an increased production of the antioxidant superoxide dismutase that was likely produced to prevent the excessive damage that occurred. Overall, the results of this study, and several others, suggest that sedentary lifestyles can lead to increased oxidative stress and vascular dysfunction.

The logical conclusion we can draw from these two cases—extreme exercise and complete inactivity—is that leading a physically active life, but not excessively active, will help keep our cells healthy, happy, and functioning to the best of their ability. Ultimately, this sort of cellular environment is exactly what you want for optimal functioning. 

This is where you will have the best chance of using the food you eat to provide fuel and nourishment, rather than storage as excess body fat. Therefore, exercise can optimize your cellular health which in turn helps you achieve your ideal body composition. 

This article was edited by Kate Findley, Writer for The Great Courses Daily.

Dr. Michael Ormsbee is an Associate Professor in the Department of Nutrition, Food, and Exercise Sciences and Interim Director of the Institute of Sports Sciences and Medicine in the College of Human Sciences at Florida State University. He received his M.S. in Exercise Physiology from South Dakota State University and his Ph.D. in Bioenergetics from East Carolina University.