While regular exercise is one of the best ways of reducing the risks of a number of diseases, including cardiovascular disease, a new study has revealed that excessive endurance exercises, such as running marathons or long distance bicycle races, could in fact be detrimental to heart health as it leads to structural changes in large arteries.
Researchers review 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," said 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," he added.
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 12percent 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 noted. He suggested 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.
The study appeared in the June issue of Mayo Clinic Proceedings.