Can you exercise too much?

Exercise and good health go hand in hand. Exercise and physical activity have been linked to protection against heart attack, stroke, diabetes, some types of cancer, dementia, and more. A little bit of exercise is better than none, and more than a little is even better. But is there an upper limit beyond which too much exercise is harmful?

For almost everyone, the answer is no. As several colleagues and I write in the latest issue of the Journal of the American College of Cardiology (JACC), the main problem in the United States and around the world is too little exercise. One-quarter of Americans don’t exercise at all; only about half hit the weekly recommendation of 150 minutes of moderate exercise (like walking) or 75 minutes of vigorous exercise (like running).

Modern life has factored exercise out of our lives. I recently took a historical tour of my hometown of Simsbury, Conn. According to the guide, in the 1700s, the average Simsbury resident burned between 4,000 and 6,000 calories a day, chopping wood, hauling water, farming, and the like. Today, most of us burn under 2,000 calories a day. In other words, we need more exercise, not less.

At the other end of the spectrum

I’ve been interested for years in whether too much exercise could somehow offset its cardiovascular benefits. Having run the Boston Marathon 29 times (finishing 16th in 1976), I know how much training is needed to run a marathon or a triathlon, to row or cycle competitively, and the like.

In the JACC article, we explored four recent studies that suggest exercising a lot may not be as good for the heart or long-term health as exercising more moderately. In these studies, people who exercised strenuously appeared to lose most of the cardiovascular benefits that exercise provided to more moderate exercisers.

It’s important to keep in mind that the number of people at the upper end of the exercise spectrum in these studies was very small. So the results should be used to generate new hypotheses, not to make recommendations about exercise. Unfortunately, the media attention these studies generated has sown some confusion among the public about the benefits — and hazards — of exercise for preventing heart disease.

That said, the results are intriguing, and there may be biological explanations for them. For example, endurance activities such as running a marathon stretch the right ventricle — the chamber of the heart that pumps blood to the lungs. This could be hazardous among individuals with a genetic predisposition for a relatively rare condition called right ventricular cardiomyopathy.

Overall, though, as a group, endurance and elite athletes who exercise at the upper end of the physical activity spectrum aren’t at increased risk for cardiovascular disease, and tend to live longer than individuals who are sedentary and those who exercise moderately.

No upper limit for exercise

Over the years, hundreds of studies have shown that exercise and physical activity are associated with lower rates of heart disease and longer life. We think this is due to exercise itself. But none of these studies has ever been able to exclude the possibility that people who choose to exercise are genetically and physiologically hardier. That might be especially true for endurance and elite athletes.

Here’s the bottom line on exercise “dose” and cardiovascular health: Any amount of exercise is better than none. Even something as simple as standing instead of sitting is beneficial. For moderate exercise, like walking, there is no upper limit, although doing it for more than 100 minutes a day doesn’t seem to convey any extra cardiovascular benefit. Vigorous activity, like jogging, can offer large cardiovascular benefits, though doses up to 10 times the recommended amount (about 12 hours a week) don’t have an extra payoff.

Paul D. Thompson, MD, is a cardiologist at the Hartford Hospital, where he is chief of cardiology, cardiovascular research, and the Athlete’s Heart Program. He is also professor of medicine at the University of Connecticut. He has received research support or consulted for various pharmaceutical and device companies and has provided expert legal testimony on exercise-related cardiac events and statin myopathy.