Legend has it that Philippides, a Greek messenger, ran 25 miles from Marathon to Athens circa 490 BC, delivered his message and promptly died. Did he die from excessive exercise? More likely he died from under exercise having not trained for his arduous run. It wasn’t until 1896 that the marathon race began and since then, millions upon millions have safely trained and completed marathons.

The question of whether someone can exercise too much has been around for decades with the debate being popularized following the death of legendary runner/author James Fixx while running at the age of 52 in 1984. As a result, many people questioned the wisdom of exercising. For Mr. Fix, his father died of a heart attack when he was 43 and an autopsy revealed blockages in his heart arteries. But since he was running alone when he died, no one knows exactly what happened, whether he experienced symptoms or how hard he was running. This only added to the mystique around the safety of exercise. While exercise may increase one’s risk for having a heart attack (albeit small), numerous studies show that exercise is good for people with heart disease.

Just the other week, a study came out stating that too much exercise may be bad for your heart. This study found that white men who exercised three times more than the physical activity guidelines (150 minutes of moderate activity per week), had greater coronary artery calcification (CAC), compared to white men not meeting the physical activity guidelines. What is remarkable about this finding is the levels of exercise that were associated with problems for the heart were quite low- only about an hour a day. This isn’t much at all and an amount that many people are already doing. Needless to say this study got a lot of media attention.

So is this study conclusive that you can do too much exercise? No.

First off this study used CAC as an indicator of effect on the heart, and not actual heart events like heart attack or death. While CAC is a marker of heart disease, it does not automatically mean someone with a high amount of CAC will have a heart attack.

Secondly, the association between exercise and higher CAC was only present in white men, but not in the white women, black men and black women also in the study. The authors of the study acknowledged that this could be a chance finding.

Lastly, and perhaps most important, is that other studies have shown that the atherosclerotic plaques in athletes tend to be of the more stable type and less likely to lead to a heart attack compared to the plaques in the physically inactive people. So it is believed that the CAC seen in athletes is actually protective.

In addition, numerous other studies have shown the protective effect of much higher levels of exercise. In our recent paper, we reported continued benefits of activity at levels 17 times that of the guidelines (effectively walking for eight hours per day). This has been confirmed in a subsequent research study.

Are you at greater risk when exercising? Yes, when being active, there is a greater risk of dying or having heart complications compared to sitting down. This risk though is extremely small; a study of women reported 1 sudden cardiac death in 36.5 million hours of exercise compared to 1 in 59.4 million hours of no exertion like sitting (this increased risk is only during the exercise session). Similar findings have also been found in men and indicate that regular exercise actually lowers the risk. To put this into perspective, a person living to 75 years only lives for 657 000 hours, so the risk is very small and it gets smaller as a person gets in better shape from exercising.

There are situations in which too much exercise could have possibly negative effects. Studies in ultramarathon runners (a 160 km run) indicate that following the event there are changes in the heart’s function and physiology that we normally consider damage to the heart in the general population. However, it’s not clear if these changes are a problem or in actual fact favourable adaptations to exercise given that people exercising consistently outlive people who don’t.

The overwhelming evidence suggests that regular activity and exercise is beneficial in terms of preventing heart and other diseases, as well as increasing lifespan. While there may be adverse effects in people who do extremely high amounts of strenuous exercise, the findings are unclear and for many of us, we are going to do nowhere near that amount of exercise. We should take pause and recognize the main problem in our society is that people don’t do enough exercise, not that they do too much.

In the next blog I will discuss how to safely exercise if you have heart disease.

This is Part 11 in a series of blog posts entitled Being Active While Living an Active Life.