Can You Exercise Too Much After a Heart Attack?

Medical science has long recognized that remaining sedentary after an ST Segment Elevation Myocardial Infarction (STEMI) (heart attack) is a major risk factor for early death. People who engage in formal cardiac rehabilitation programs after a heart attack, and then continue exercising once the formal rehab program has ended, are known to do much better for much longer than people who remain (or become) inactive. This is why regular exercise is emphasized by doctors who treat patients with coronary artery disease (CAD).

Older adult couple running on the beach
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The idea that there may be such a thing as “too much” exercise after a heart attack is a new one. Or rather, it is a new formulation of an old idea—50 years ago heart attack victims were routinely treated with weeks of bed rest, and as a result, often became permanent invalids. That there might be such a thing as too much exercise after a heart attack has been raised anew by a research paper appearing in August 2014 in the Mayo Clinical Proceedings. This paper suggests that, while regular exercise after a heart attack substantially and significantly reduces the risk of death, the benefits of exercise may begin to reverse once a certain threshold is reached.

Specifically, the authors suggest, heart attack survivors who run more than about 31 miles per week, or who walk briskly for more than about 46 miles per week, have a higher risk of dying than runners (or walkers) who exercise less than those amounts. (However, they are still significantly better off than heart attack survivors who are sedentary.)

The Evidence for an Exercise Threshold

This evidence comes from the National Runners’ Health Study and the National Walkers’ Health Study. These studies recruited over 100,000 participants, who filled out a series of questionnaires about their medical history and exercise habits. Of these participants, 924 males and 631 females reported that they had prior heart attacks, and these were the people included in the study we’re discussing.

Here is what the investigators found. After being followed for about 10 years, participants who ran up to 8 miles per week or walked up to 12 miles per week (which is roughly the distance a person would achieve who follows typical post-heart attack exercise guidelines), reduced their heart disease-related mortality by 21%, compared to sedentary heart attack survivors. Mortality was reduced by 24% for people who ran 8–16 miles or walked 12–23 miles per week; by 50% for those who ran 16–24 miles or walked 23–34 miles per week; and by 63% for people who ran 24–31 miles or walked 34–46 miles per week.

However, in heart attack survivors who really pushed their exercise, to the point that they ran more than 31 miles or walked more than 46 miles per week, only a 12% reduction in mortality was seen - which is only about half the benefit achieved by people who “merely” followed current exercise guidelines. So, from this study, it appears that the more exercise you do after a heart attack the greater the benefit—up to a point. But beyond that point—once an apparent exercise threshold is reached—the mortality benefit of the exercise actually begins to reverse.

The authors of an editorial appearing in the same issue of the Mayo Clinical Proceedings speculated that perhaps there is such a thing as “cardiac overuse injury,” in which too much exercise may actually reduce cardiac health (perhaps by producing scar tissue in the heart and thus cardiomyopathy). If so, then there may indeed be such a thing as “too much” exercise, at least in people who have had heart attacks.

Is This Really True?

It may indeed be true that doing “too much” exercise after a heart attack can attenuate much of the benefit you gain by performing regular exercise. However, there are important limitations to this study that require us to put its conclusions into perspective.

First, this study was done by questionnaire only. We have to take the participants’ word for the amount of exercise they performed, and perhaps more importantly, for the fact that they actually had heart attacks. (Doctors sometimes use the term “heart attack” loosely and imprecisely, and their patients may come away with a mistaken impression.) So at some level, the accuracy of the data itself may be questioned. This, of course, is an inherent limitation of any medical study that relies solely upon questionnaires for its data.

Perhaps more important is a finding that becomes apparent when one views the table of data published with the article itself. From that table, it is apparent that heart attack survivors who ran more than 31 miles per week were, on average, a lot younger than people who ran less. In fact, they averaged only 51 years of age. And furthermore, they apparently had their heart attacks an average of 13 years before they were enrolled in this study, or (on average) at age 38. The authors of the article do not directly address the implications of this age discrepancy.

But we know that people who have heart attacks at an early age often have a relatively aggressive form of CAD, and their heart disease can be more progressive and more difficult to treat than for typical patients with CAD. So, perhaps the increase in mortality seen in people who ran more than 31 miles per week wasn’t caused by the exercise at all. Instead, maybe this was just a different population of heart attack patients.

Bottom Line

The headlines that were widely broadcast as a result of this study claim that “Too much exercise after a heart attack can kill you!” While it may be true that doing too much exercise after a heart attack may attenuate the benefits of the exercise, we need to keep a few things in mind as we think about what this study really means.

First, this study does not prove anything; it is too an imperfect a study to do any more than generate a new hypothesis that needs to be tested in prospective clinical trials.

Second, the “exercise threshold” which was apparently identified in this study, beyond which exercise may become harmful after a heart attack, is really quite high. Anyone who is running more than 31 miles or walking more than 46 miles per week has probably reorganized their entire lives around their exercise routines. Very few survivors of heart attacks are chronically exercising anywhere near the level where there is any reason for concern.

And most importantly, regardless of whether there is such a thing as “too much” exercise after a heart attack, this study confirms once again that regular exercise after a heart attack—even levels of exercise most heart attack survivors would never attempt to maintain—is related to a substantial improvement in cardiac outcomes. Regular exercise, this study confirms, is extremely important to your health after a heart attack.

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  • O'Keefe JH, Franklin B, Lavie CJ. Exercising for health and longevity vs peak performance: Different regimens for different goals. Mayo Clin Proc 2014; DOI:10.1016/j.mayocp.2014.07.007.
  • Williams PT, Thompson PD. Increased cardiovascular disease mortality associated with excessive exercise in heart attack survivors. Mayo Clin Proc 2014; DOI:10.1016/j.mayocp.2014.05.006.

By Richard N. Fogoros, MD
Richard N. Fogoros, MD, is a retired professor of medicine and board-certified in internal medicine, clinical cardiology, and clinical electrophysiology.