(RxWiki News) Endurance exercises such as running and bicycling benefit overall health and improve longevity. However, there appears to be a point where too much of a good thing is possible.
Excessive amounts of endurance training can injure the heart, leading to an increased risk of developing atrial fibrillation, a common heart rhythm disorder.
"Engage in regular exercise, but don't overdo it."
James H. O'Keefe, MD, a lead author from Saint Luke's Hospital, noted that, though generally beneficial, physical exercise posses many traits of a powerful drug. As with any drug, a safe upper dose limit exists at which point adverse effects of exercise such as musculoskeletal trauma and cardiovascular stress may outweigh benefits, he said.
During the study, investigators reviewed recent literature regarding potential harm to the heart from engaging in chronic excessive endurance exercise.
Previous research has suggested too much physical activity, particularly endurance exercise activities such as marathons and triathlons, may lead to structural heart changes, enlarged arteries and an increased risk of heart injury, including atrial fibrillation.
Researchers found that extreme endurance training causes temporary structural cardiovascular changes and elevations of cardiac biomarkers, with levels returning to normal about a week later. However in athletes that engage in excessive training, repetitive injury can lead to the thickening of heart valves, commonly seen in heart failure patients, and potentially fatal heart arrhythmias.
They found that 12 percent of healthy marathon runners examined during the study had evidence of heart scarring.
During a two year follow up period, those runners were found to be at a significantly higher risk of coronary heart disease as compared to individuals who do not engage in excessive endurance training.
Such chronic exercise also may be linked to coronary artery calcification, abnormalities in heart function and large-artery wall stiffening.
Dr. O'Keefe said that after 30 to 60 minutes of extreme daily exercise, patients may no longer reap the benefits of physical activity. Endurance exercise in general is not conducive to strong cardiovascular health as compared to regular, more modest physical activity, he said.
The review study was recently published in the June issue of Mayo Clinic Proceedings.