Cardiovascular risks for excessive endurance training highlighted

By MedWire Reporters

Ironman triathlons, ultramarathons, and even marathons are potentially associated with a risk for adverse cardiovascular effects.

Over months to years of training, some individuals may develop myocardial fibrosis, which can lead to the development of arrhythmias, while others may develop calcification in the coronary arteries.

These are the conclusions of a new review by James O'Keefe (Mid America Heart Institute, Kansas City, Missouri, USA) and colleagues in Mayo Clinic Proceedings.

Based on animal and human data, the cardiovascular benefits of vigorous aerobic exercise training "accrue in a dose-dependent fashion up to about one hour daily, beyond which further exertion produces diminishing returns," they state.

In the review, the researchers are quick to point out that individuals who exercise have significantly lower rates of disability and longer life expectancy. In one observational study with 15 years of follow up, runners had a 19% lower risk for all-cause mortality compared with nonrunners.

However, the relationship between running and survival was U-shaped, which suggested that longer durations, such as distances of more than 20 miles per week, were associated with a loss of the mortality benefit.

O'Keefe and colleagues say that extreme endurance events can cause transient volume overload of the atria and right ventricle, which can lead to reductions in the right ventricle ejection fraction and elevations in cardiac biomarkers. These changes typically return to normal 1 week after the race.

However, "over months to years of repetitive injury, this process, in some individuals, may lead to patchy myocardial fibrosis," which in turn creates a substrate for atrial and ventricular arrhythmias.

Some studies of veteran marathoners, ultramarathoners, and professional cyclists have shown that these individuals have rates of atrial fibrillation five times higher than the general population, report O'Keefe and colleagues.

In addition, long-term excessive endurance training can lead to coronary artery calcification, diastolic dysfunction, and large-artery wall stiffening, they add.

The group notes there are no proven screening methods for detecting potential cardiovascular pathologic changes with extreme endurance events, although postcompetition cardiac biomarker assessment, echocardiography, and/or cardiac imaging such as magnetic resonance imaging might be used to screen at-risk individuals.

Further studies are still needed to identify exercise thresholds for potential toxicity, especially in high-risk athletes.

Consensus guidelines from numerous organizations, including the American Heart Association, call for 150 minutes of moderate exercise, or 75 minutes of vigorous exercise, per week. The guidelines also caution that high-intensity exercise does increase the risk for adverse cardiovascular events.

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