WASHINGTON, D.C. (WUSA) -- People who participate in marathons, iron man distance triathlons and very long distance bicycle races are usually thought of as some of the fittest people around. Research from the Mayo Clinic, however, shows excessive endurance training can overwhelm the heart.
The lead author of the study, James O'Keefe, MD, of Saint Luke's Hospital of Kansas City, MO, says that "physical exercise, though not a drug, possesses many traits of a powerful pharmacologic agent." This means that daily exercise can work wonders to treat many diseases, but if it is excessive, the negatives may outweigh the benefits.
Dr. O'Keefe and his team released data suggesting that extreme endurance training structural cardiovascular changes and heightened cardiac biomarkers which return to normal within one week. For some people, after months the constant changes can lead to the development of patchy myocardial fibrosis and an increased susceptibility to atrial and ventricular arrhythmias.
In one study, nearly 12 percent of healthy marathon runners showed evidence for patchy myocardial scarring.
Certified Personal Trainer Zak Kaplan of Washington Sports Clubs says cardiovascular exercise is much better than being sedentary, but there are potential problems for your heart.
Kaplan says, "When you're stressing it at a cardiovascular level, it's being pushed past normal everyday life, it's forced to become stronger, become efficient, become bigger in some cases. And if it's not given enough time to recover, you run the risk of the heart physically growing in size, physically creating scarring tissue, things like that that can cause long term problems down the road."
Additional evidence for this study lies in the death of Micah True, a legendary ultra-marathoner. True died suddenly while on a routine 12-mile training run, but he was known to run as far as 100 miles a day. Doctors suspect his lethal arrhythmia may have been a result of Phidippides cardiomyopathy, which is caused by chronic excessive endurance exercise.
Despite this, O'Keefe stresses that physical exercise is still incredibly important. Extreme exercise can be dangerous, but 30 to 60 minutes per day is healthy for most people.