The Negative Consequences of Long-Distance Endurance Training

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They are considered some of the top athletes of our time, those who can endure the grueling hardship of a 25 mile run, a 150 mile bike ride, or a 5 mile swim. They are our marathoners, triathletes, and long distance cyclists. Their bodies are finely tuned machines enhanced to accomplish one task: get from point A to point B as fast as possible by whatever means is at their disposal. However, a recent study suggests competing in these extreme endurance contests, and the chronic training associated with them can cause structural changes to the heart and large arteries, leading to myocardial injury (injury to the muscular tissue of the heart).

They are considered some of the top athletes of our time, those who can endure the grueling hardship of a 25 mile run, a 150 mile bike ride, or a 5 mile swim. They are our marathoners, triathletes, and long distance cyclists. Their bodies are finely tuned machines enhanced to accomplish one task: get from point A to point B as fast as possible by whatever means is at their disposal. However, a recent study suggests competing in these extreme endurance contests, and the chronic training associated with them can cause structural changes to the heart and large arteries, leading to myocardial injury (injury to the muscular tissue of the heart).

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The research was led by James H. O'Keefe, MD, of Saint Luke's Hospital in Kansas City, Missouri. O'Keefe says physical exercise has many traits in common with powerful pharmacological agents. Like prescription drugs, the exercise can be used to prevent and as treatment for many diseases, including coronary heart disease, hypertension, heart failure, and obesity.

"However," said Dr. O'Keefe, "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 researchers data show that extreme endurance training can cause transient structural cardiovascular changes and elevations of cardiac biomarkers, which normally return to normal within one week.

But for some individuals who suffer repeated injuries over months and years, this process can lead to the development of patchy myocardial fibrosis, abnormal thickening or scarring of the cardiac tissue. This happens particularly in the atria, interventricular septum, and right ventricle. It can also lead to an increased chance of atrial and ventricular arrhythmias.

They found that 12% of seemingly healthy marathon runners had evidence of patchy myocardial scarring, and a higher chance of coronary heart disease after a two-year follow up exam compared with a control group.

The research suggests that the cardiac remodeling caused by excessive heavy exercise can lead to rhythm abnormalities, coronary artery calcification, diastolic dysfunction, and large-artery wall stiffening.

Ultra-marathon running and professional cycling have also been associated with an up to 5-fold increase in the risk of atrial fibrillation. However, O'Keefe notes that lifelong vigorous exercisers typically have lower mortality and disability rates than others. More research is required to see which individuals would be more at risk for adverse cardiovascular remodeling.

This study has been published in the journal, Mayo Clinic Proceedings.

Video interview with James O'Keefe: http://www.youtube.com/watch?v=jp_zviTtIQk

Cycling image via Shutterstock