Excessive Endurance Training Can Be Fatal

(Ivanhoe Newswire) – Legendary ultra-marathoner Micah True suddenly died while on his typical 12-mile training run on March 27, 2012. The 58-year-old’s best-selling book, Born to Run, documents that he would run as far as 100 miles in a day. Doctors determined he died of a lethal arrhythmia (irregularity of the heart rhythm) after his autopsy revealed his enlarged and scarred heart. His death points towards possible manifestations of "Phidippides cardiomyopathy," a condition spurred by chronic excessive endurance exercise.

Exercise is often touted for its benefits in preventing and treating many common chronic diseases and improving cardiovascular health. However, recent studies show that excessive endurance training such as marathons, iron man distance triathlons and long distance bicycle races may cause structural changes to the heart and large arteries which can lead to myocardial injury.

"Physical exercise, though not a drug, possesses many traits of a powerful pharmacologic agent. 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," lead author James H. O'Keefe, MD, of Saint Luke's Hospital of Kansas City, MO, was quoted as saying. "However, as with any pharmacologic agent, a safe upper dose limit potentially exists, beyond which the adverse effects of physical exercise, such as musculoskeletal trauma and cardiovascular stress, may outweigh its benefits."

The research data suggests that extreme endurance training can cause transient structural cardiovascular changes and elevations of cardiac biomarkers, all of which return to normal within one week.

For some people, after months and years of repetitive injury, extreme training can lead to the development of patchy myocardial fibrosis, particularly in the atria, interventricular septum, and right ventricle, and an increased susceptibility to atrial and ventricular arrhythmias. In one study, approximately 12% of apparently healthy marathon runners showed indication 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.

It has been commonly recognized that elite-level athletes develop abnormal electrocardiograms and atrial and ventricular entropy, but these adaptations have not previously been thought to lead to serious arrhythmias or sudden cardiac death.

It now appears that excessive exercise-induced cardiac remodeling can lead to rhythm abnormalities. Sports like ultramarathon running and professional cycling have been associated with as much as a 5-fold increase in the incidence of atrial fibrillation. Excessive endurance exercise may also be associated with coronary artery calcification, diastolic dysfunction, and large-artery wall stiffening.

Further investigation is needed to identify who is at risk for adverse cardiovascular remodeling and to develop fitness regimens to optimize the cardiovascular health of endurance athletes.

Despite these study findings, it is still important to place emphasis on physical exercise. Dr.O’Keefe is quoted as saying, “Extreme exercise is not really conducive to great cardiovascular health. Beyond 30-60 minutes per day, you reach a point of diminishing returns.”

Source: Mayo Clinic Proceedings, June 2012