Too much endurance running, cycling might weaken the heart

Physicians increasingly are prescribing exercise for patients to help them maintain a healthy weight and prevent obesity-related illnesses, such as diabetes and hypertension.

While research shows that moderate physical activity improves wellness, studies indicate that too much exercise, particularly extreme endurance events, such as ultramarathons, can have adverse cardiovascular effects, says a report in the June issue of Mayo Clinic Proceedings. An ultramarathon is a footrace that extends beyond the standard marathon distance of 26 miles.

The cardiovascular problems that can result from repeated endurance exercise include atrial and ventricular arrhythmias, coronary artery calcification and diastolic dysfunction, the report said.

Study co-author and cardiologist Carl. J. Lavie, MD, said there is no clear moment when healthy exercise becomes an excessive behavior that could cause more harm than good. But he said physicians should be aware of the potential dangers and discuss those risks with patients.

“We're not saying people shouldn't run a marathon, but it's worth people knowing that there are risks,” said Dr. Lavie, medical director of cardiac rehabilitation and prevention at the Ochsner Medical Center in New Orleans.

In general, running boosts health, data show. Runners have a 19% lower risk of all-cause mortality compared with nonrunners, according to a separate 15-year observational study of 52,656 adults 20 and older. The unpublished study was presented on June 2 at the American College of Sports Medicine meeting in San Francisco. Dr. Lavie also was co-author of that study.

People did not have to run far or often to receive those benefits. Running two to five days a week, for up to 20 miles per week, was associated with lower all-cause mortality, the study said.

“Physical exercise, though not a drug, possesses many traits of a powerful pharmacologic agent,” said James H. O'Keefe, MD, lead author of the Mayo Clinic Proceedings report and a cardiologist at 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.”

Dangers of excessive exercise

The Mayo report reviewed about 50 studies published between 1991 and 2012 on the health effects of extreme endurance training and competition. One study showed that about 12% of apparently healthy marathon runners had evidence of patchy myocardial scarring. The coronary heart disease rate during a two-year follow-up was significantly higher in marathon runners than in controls.

Endurance sports, including professional cycling, have been associated with up to a fivefold increase in the prevalence of atrial fibrillation, the Mayo report said.

Likely causing these cardiovascular problems are repeated structural changes to the heart that occur due to excessive endurance training or competition, Dr. Lavie said. When people partake in those activities multiple times over years, scar tissue can form in the heart and weaken the muscle or cause a rhythm disturbance, he said.

Although the findings are concerning, sports medicine physician R. Amadeus Mason, MD, said it's important to understand that excessive endurance athletes represent a small percentage of the population. Before those individuals experience cardiovascular problems, they often exhibit other warning signs, such as musculoskeletal injuries, he said.

If patients start coming in with “tendinitis, stress fractures and other overuse issues, that's a warning sign that they're doing too much for their body” and they should cut back, said Dr. Mason, assistant professor in the orthopedics and family medicine departments at Emory University School of Medicine in Atlanta. He also is a team physician for USA Track and Field, the national governing body for track and field, long-distance running and race walking in the United States.

There are no proven screening methods for detecting potential cardiovascular changes associated with extreme endurance exercise. Instead of using costly tests, Dr. Lavie recommends that physicians ask patients about their exercise habits and offer suggestions on how they can change their workout routines to make them safer.

For example, if a patient says he or she runs 15 miles a day, the doctor could recommend reducing the distance to five or so miles, Dr. Lavie said.

The American Heart Assn. is updating its exercise standards, said AHA spokesman Gerald Fletcher, MD. The current recommendation for adults calls for at least 150 minutes per week of moderate exercise or 75 minutes a week of vigorous activity.

“The health benefits of an ultramarathon are no more than the long-term benefits of moderate exercise,” said Dr. Fletcher, a professor of medicine in the cardiovascular diseases department at Mayo Medical School in Jacksonville, Fla.