Can You Exercise Too Much?

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Dr. John Swartzberg is an internist and specialist in infectious disease, and chairman of the editorial board of the UC Berkeley Wellness Letter and berkeleywellness.com. He is also a clinical professor emeritus of medicine at the University of California, Berkeley School of Public Health. He contributed this article to Live Science's Expert Voices: Op-Ed & Insights.

Most of us wish we exercised more. After all, fewer than half of us get the recommended amount of physical activity, and we know it. But is it possible to get too much of a good thing?

It turns out that the answer is yes. Exercise provides many health benefits, but at some point working out too hard or too long increases the risk of injury and other adverse effects. That usually only happens with intense exercise, like training for marathons or endurance activities. Such challenging activities are perfectly fine, maybe even laudable endeavors, but if you're looking for optimal health benefits, research suggests that more moderate workouts are generally the way to go.

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In a British study of more than a million healthy middle-aged women in Circulation, those who were physically active at least once a week were less likely to have heart attacks, strokes or venous thromboembolic events (blood clots in the legs or lungs) over a nine-year period than inactive women. Moreover, any type of physical activity, including gardening and housework, had pretty much the same effects as strenuous activity. But what made headlines was that the women who exercised every day didn't benefit more than the less frequent exercisers. In fact, they were at greater risk. The women who exercised at least two times a week, and no more than six times, had the lowest cardiovascular risk, compared to infrequent or daily exercisers.

Similarly, a large Danish study in the Journal of the American College of Cardiology, which compared the mortality rates of 1,098 healthy joggers and 3,950 sedentary people, found that those who did light to moderate running (in terms of pace, duration and frequency) were less likely to die over a 12-year period than non-exercisers. But strenuous joggers — fast pace, more than 2 1/2 hours a week, or more than three times a week — had a mortality rate similar to sedentary people. The researchers concluded: "…higher doses of running are not only unnecessary but may also erode some of the remarkable longevity benefits conferred by lower doses of running."

Other studies have found that sedentary people are at higher risk than daily exercisers, but moderate exercisers fared better than both. For instance, a German study in the journal Heart looked at 1,038 people who had stable coronary heart disease and found that both those who were sedentary and those who exercised every day (or did more than about 15 hours of strenuous activity a week were more likely to die over a 10-year period than those who exercised several times a week — but the risk was greatest for the couch potatoes.

Notably, is there something about people who overdo strenuous endurance exercise that harms their health? Perhaps they are overly competitive or compulsive and tend to overdo other things as well. In contrast, do people who exercise moderately also do other things in moderation, which is generally a healthy way to live? Researchers try to control for such factors, but the likelihood that some such factors are not identified or adjusted for remains a concern.

Dr. John Swartzberg writes about health and wellness, particularly issues that affect overall public health in the United States. He is an internist and specialist in infectious disease and is chair of the editorial board of the UC Berkeley Wellness Letter and berkeleywellness.com. He is also a clinical professor emeritus of medicine at the University of California, Berkeley School of Public Health and the University of California, San Francisco School of Medicine. When not writing and advising, he enjoys running, reading and playing with his grandchildren.