Examining the Controversy: Is too much exercise bad for the heart?

swimming in triathlon  

The mainstream media claims recent research may show vigorous exercise is unhealthy. That isn’t the complete picture.

 

 

A flurry of studies  a few years ago suggesting too much exercise is detrimental to one’s health sparked fierce debate over the legitimacy of the claims. The mainstream media jumped into the fray. The Wall Street Journal published an article “One Running Shoe in the Grave” arguing too much exercise stresses the heart enough to erase any physical activity health gains. What did the studies actually find, and is it a cause for concern?

One study tracking 52,000 adults for 15 years found that runners had a 19% decrease in all-cause mortality. However, when it was broken down by mileage a U-shaped curve emerged. Those exercising moderately for 2-5 days a week had the lowest mortality. The extremes had the highest mortality. In fact, the people running more than 25 miles a week had almost as high a mortality rate as those not exercising at all. The figure below shows this “U-curve” from the study (Running and all-cause mortality risk: is more better? 2012. Lee J, et al.)

However this does not give the complete picture. Another study, published in 2011, found that vigorous exercise and moderate exercise had differing amounts of benefit towards reducing mortality risk. The authors found that moderate exercise showed a gentle, increasing curve when plotted against mortality risk.  Meanwhile, vigorous exercise had far higher marginal returns up to about 50-60 minutes a week when it began to plateau. For both vigorous and moderate exercise, diminishing returns was observed as expected. However, no negative relationship was seen with extreme durations of daily exercise. The relationship can be seen in the figure below (Minimum amount of physical activity for reduced mortality and extended life expectancy: a prospective cohort study, 2011. Wen CP, et al.)

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So although the relationship cannot be fully established, if vigorous exercise does cause an increase in mortality risk past a certain point what is the cause?  According to a review by cardiologist James O’Keefe and colleagues, the cause is a problem with heart function.  (Potential Adverse Cardiovascular Effects From Excessive Endurance and Exercise, 2012.  James O’Keefe, et al.). Athletes develop an enlarged left ventricle to enable increased circulation. This remodeling does not disappear for at least several years following retirement from vigorous exercise. Several biomarkers for myocardial damage appear to be elevated following intense, prolonged races such as triathlons or marathons.  Myocardial scarring from vigorous exercise may lead to problems. Endurance athletes have been shown to have a higher rate of electrocardiogram problems.  Endurance athletes may have a five-fold increase in prevalence of atrial fibrillation. The increase in atrial size from endurance training may be responsible for atrial fibrillation.

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Other problems with the cardiovascular system that show up in endurance athletes include coronary artery calcification, diastolic dysfunction, aorta wall stiffening and myocardial fibrosis. Despite all these potential problems the authors add that lifelong vigorous exercisers generally have low mortality and great cardiovascular function; its an interesting paradox.

In conclusion, if health is your sole reason for exercising it may be best to limit exercise to 2-5 days a week of moderate exercise. However, the risks of vigorous exercise are highly speculative until more research comes out. The mainstream media is likely exaggerating the findings of recent studies or drawing hypothetical conclusions. When carefully looking at the data and the papers collectively, the research says vigorous exercise is still good for the body. Regardless of which side ultimately wins the debate, exercise is undoubtedly good for the mind and collective well-being.