According to, 529,435 people finished marathons in the United States and Canada in 2012. Although marathon running is a popular sport, recent research warns that “amateur runners” who participate may increase their cardiac risk.

The study, published in the Canadian Journal of Cardiology (2013; 29 [10], 1269–76), recruited 20 recreational long-distance runners, aged 18-60, who were planning to run the Quebec City Marathon. Subjects had no known history of heart disease and were examined at four intervals throughout the study: 6–8 weeks before the race; on race day; 48 hours after the race; and 3 months after the race.

Researchers observed that in half of the runners, the marathon triggered decreases in left and right ventricular function, sometimes resulting in swelling and reduced blood flow in the heart. The decreased function was more prominent in those with “poorer peak training distance, training time and fitness level.”

“Change in global left ventricular ejection fraction was associated with VO2max,” the authors explained. “Overall, 36% of segments developed edema, 53% decreased function and 59% decreased perfusion. Significant agreement was observed between segment[s] decreasing function, decreasing perfusion, and developing edema.”

The researchers added that the changes were reversible by the 3-month mark.

“Completing a marathon leads to localized myocardial edema, diminished perfusion, and decreased function occurring more extensively in less trained and [less] fit runners. Although reversible, these changes might contribute to the transient increase in cardiac risk reported during sustained vigorous exercise,” the authors concluded.

Ryan Halvorson

Ryan Halvorson is an award-winning writer and editor. He is a long-time author and presenter for IDEA Health & Fitness Association, fitness industry consultant and former director of group training for Bird Rock Fit. He is also a Master Trainer for TriggerPoint.

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