Excessive Endurance Training Can Be Too Much of a Good Thing, Research Suggests

Regular, moderate exercise most beneficial, Mayo Clinic Proceedings reports


Rochester, MN, June 4, 2012 – Micah True, legendary ultra-marathoner, died suddenly while on a routine 12-mile training run March 27, 2012. The mythic Caballo Blanco in the best-selling book, Born to Run, True would run as far as 100 miles in a day. On autopsy his heart was enlarged and scarred; he died of a lethal arrhythmia (irregularity of the heart rhythm). Although speculative, the pathologic changes in the heart of this 58 year-old veteran extreme endurance athlete may have been manifestations of "Phidippides cardiomyopathy," a condition caused by chronic excessive endurance exercise.

Regular exercise is highly effective for the prevention and treatment of many common chronic diseases, and improves cardiovascular health and longevity. However, recent research suggests that chronic training for, and competing in, extreme endurance exercise such as marathons, iron man distance triathlons, and very long distance bicycle races may cause structural changes to the heart and large arteries, leading to myocardial injury. A study in the June issue of Mayo Clinic Proceedings reviews the literature and outlines in detail for the first time the mechanisms, pathophysiology, and clinical manifestations of cardiovascular injury from excessive endurance exercise.

“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,” says lead author James H. O’Keefe, MD, of Saint Luke’s Hospital of Kansas City, MO. “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.”

Dr. O’Keefe and his colleagues present emerging data suggesting 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 individuals, over months and years of repetitive injury, this process 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 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.

Although it has been recognized that elite-level athletes commonly develop abnormal electrocardiograms and atrial and ventricular entropy, these adaptations traditionally have not been thought to predispose to serious arrhythmias or sudden cardiac death. However, it now appears that the cardiac remodeling induced by excessive exercise can lead to rhythm abnormalities. Endurance sports such as ultramarathon running or professional cycling have been associated with as much as a 5-fold increase in the prevalence of atrial fibrillation. 

Chronic excessive sustained exercise may also be associated with coronary artery calcification, diastolic dysfunction, and large-artery wall stiffening.

Lifelong vigorous exercisers generally have low mortality and disability rates and excellent functional capacity, Dr. O’Keefe notes. He suggests that further investigation is needed to identify who is at risk for adverse cardiovascular remodeling, and to formulate physical fitness regimens for conferring optimal cardiovascular health and longevity.

In a video interview accompanying the article ( http://www.youtube.com/watch?v=jp_zviTtIQk), Dr. O’Keefe stresses that the report does not detract from the importance of physical exercise. “Physically active people are much healthier than their sedentary counterparts. Exercise is one of the most important things you need to do on a daily basis,” he explains. “But what this paper points out is that a lot of people do not understand that the lion’s share of health benefits accrue at a relatively modest level. Extreme exercise is not really conducive to great cardiovascular health. Beyond 30-60 minutes per day, you reach a point of diminishing returns.” 

 

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Notes for Editors
“Potential Adverse Cardiovascular Effects From Excessive Endurance Exercise,” by James H. O’Keefe, MD, Harshal R. Patil, MD, Carl J. Lavie, MD, Anthony Magalski, MD, Robert A. Vogel, MD, and Peter A. McCullough, MD, MPH. Mayo Clinic Proceedings, Volume 87, Issue 6 (June 2012), DOI: 10.1016/j.mayocp.2012.04.005, published by Elsevier.

Full text of the article is available to credentialed journalists upon request. Contact Eileen Leahy at +1 732 238 3628 or mcpmedia@elsevier.com to obtain copies. Journalists wishing to set up interviews with the authors should contact Dr. James H. O’Keefe at +1 816 751 4080 or jokeefe@saint-lukes.org.

A video interview of Dr. O’Keefe discussing in depth the importance of daily moderate physical activity, and the risk of excessive endurance exercise, can be found at http://dl.dropbox.com/u/1648108/Videos/Author%20interviews/87_6/8706okeefevideofinal.wmv

About the Authors
James H. O’Keefe, MD, Saint Luke’s Hospital of Kansas City, MO
Harshal R. Patil, MD, Saint Luke’s Hospital of Kansas City, MO
Carl J. Lavie, MD, Ochsner Clinical School of Medicine, New Orleans, LA, and Pennington Biomedical 
Research Center, Louisiana State University System, Baton Rouge
Anthony Magalski, MD, Saint Luke’s Hospital of Kansas City, MO
Robert A. Vogel, MD, University of Maryland, Baltimore, MD
Peter A. McCullough, MD, MPH, St. John Providence Health System Providence Park Heart Institute, Novi, MI

About Mayo Clinic Proceedings
The flagship journal of Mayo and one of the premier peer-reviewed clinical journals in general medicine, Mayo Clinic Proceedings is among the most widely read and highly cited scientific publications for physicians, with a circulation of approximately 124,000. While the Proceedings is sponsored by Mayo Clinic, it welcomes submissions from authors worldwide, publishing articles that focus on clinical medicine and support the professional and educational needs of its readers. The journal’s mission is to promote the best interests of patients by advancing the knowledge and professionalism of the physician community. www.mayoclinicproceedings.org

About Mayo Clinic
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About Elsevier

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Media contact
Eileen Leahy
Elsevier
+1 732 238 3628
mcpmedia@elsevier.com