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Marathon gives heart a beating, but not for long

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Can too much exercise be detrimental to your health?

This is one of the questions my research program at the University of Manitoba and St. Boniface Hospital set out to answer.

As the population in Canada continues to increase over the next 25 years, the proportion of individuals participating in positive healthy behaviours and increased physical activity will increase accordingly.

In the primary prevention effort against cardiovascular disease, it is important to develop and evaluate strategies that may favourably affect the fitness and body composition of the average Canadian.

Physical fitness has been shown to be an independent, long-term predictor of reduced morbidity and mortality from cardiovascular causes. Although the cardiovascular effects of moderate exercise are well established, the effects of acute prolonged exertion, including marathon running, are less clear.

As marathon participants have relatively standardized diets, training regimens and distances run, they represent the benchmark population against which the safety of endurance activity in amateur individuals can be determined.

Marathon running, involving the participation of both amateur and elite Canadian athletes, has increased in popularity over the past decade. Long-term endurance training is associated with an increase in the size and thickness of the left side of the heart, a condition known as "athlete's heart." This remodelling of the heart's shape is generally understood and popularized enough that it has its own Wikipedia page.

What is not entirely understood, however, is the acute effects of marathon running on the right side of the heart.

Over the past decade, I have been fortunate to study more than 200 marathon participants, young and old, amateur and elite, competing in both the half and full marathons. Using blood tests and cardiac imaging including echocardiography (ultrasound of the heart) and MRI, we have demonstrated that marathon running causes only short-term cardiac dysfunction, but does not result in permanent heart-muscle damage.

In the 2004 and 2005 Boston Marathons and the 2006 to 2011 Manitoba Marathons, we studied marathon participants who underwent cardiac blood tests, echocardiography and cardiac MRI prior to, immediately following and one week after the marathon.

Cardiac biomarkers, which assess cardiac stress, were elevated in all athletes post-race, but normalized one week later. The imaging tests consistently demonstrated a temporary swelling and a decrease in the pumping function of the right side of the heart that completely resolved one week following the marathon.

This holds true for both amateur and elite athletes of any age competing in races from 13.1 to 26.2 miles in length.

And now it's time for a medical disclaimer: If you are a novice planning on running a marathon, consider consulting your physician first.

If you have a history of heart disease or suspicious symptoms of chest pain or shortness of breath, you should talk to a doctor prior to starting a training program.

A marathon isn't something you just show up at. Make sure you train appropriately.

During the race itself, keep yourself well-hydrated. The take-home message is that with appropriate training and fluid hydration, there is no permanent damage to the heart from strenuous physical activity due to marathon running.

Although your heart may take a temporary beating, rest assured, it will keep on ticking.


Dr. Davinder Jassal is an associate professor of medicine, radiology and physiology at the University of Manitoba and the principal investigator of the Cardiovascular Imaging Laboratory at the Institute of Cardiovascular Sciences at St. Boniface Hospital Research.


The Learning Curve is an occasional column written by local academics who are experts in their fields. It is open to any educator from Winnipeg's post-secondary institutions. Send 600-word submissions and a mini bio to

Republished from the Winnipeg Free Press print edition June 9, 2012 J12

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