Extreme endurance exercise can cause heart damage: report

TORONTO – As the saying goes, too much of anything isn’t good for you – even when it’s supposed to be good for you – like exercising.

A new study published online by Mayo Clinic Proceedings, a first of its kind, suggests that ‘excessive endurance exercise’- marathons, long-distance cycling and ultra-marathons – can cause cardiovascular damage.

According to the study, approximately 12 per cent of apparently healthy marathon runners showed evidence for ‘patchy myocardial scarring, and the coronary heart disease event rate during a two-year follow up was significantly higher in marathon runners than in controls.’

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“What we’re concerned about is people doing extreme exercise, ultra-marathons and marathons,” said Dr. James O’Keefe, clinical cardiologist from Saint Luke’s Mid American Heart Institute in Kansas City and co-author of the study.

“A routine of daily physical activity can be highly effective for prevention and treatment of many diseases,including coronary heart disease, hypertension, heart failure, and obesity,” says O’Keefe. “However, as with any pharmacologic agent, a safe upper dose limit potentially exists.”

The study also showed that excessive sustained exercise may also be associated with coronary artery calcification and large-artery wall stiffening. All of these conditions may lead to dangerous arrhythmia, or irregular heartbeats, and possible sudden cardiac death. 

So how much should we exercise? O’Keefe says running distances of two to four miles at a time is plenty, jogging rather than hard-core running is also beneficial, and walking is always a good option. He says 30-60 minutes a day of continued exercise is enough.

O’Keefe stresses that this paper in no way detracts from the importance of exercise. He says physically active people are healthier than those who aren’t.

“Don’t mistake what we’re talking about,” said O’Keefe. “A lot of people misunderstand that if moderate exercise is good, then more is better. From a fitness standpoint, most of the lion’s share of the benefits of exercise accrue at modest levels.”