June 4, 2012 -- Exercisers who train chronically to compete in marathons, triathlons, and other long-distance events may be hurting their heart health, according to a new report.
"Chronic extreme endurance efforts, like marathons, ultra-marathons, and long-distance triathlons, can cause cardiovascular damage over time," says researcher James H. O'Keefe, MD, director of preventive cardiology at the Mid America Heart Institute at St. Luke's Health System, Kansas City.
"Healthier exercise patterns involve not such extreme duration or intensity," he tells WebMD.
His multi-study review is in Mayo Clinic Proceedings.
In another study, researchers found that running at moderate speeds was linked with a lower risk of death from any cause compared to no running. More intense running didn't yield additional benefit.
That study was reported Saturday at the American College of Sports Medicine annual meeting.
The message is not to fear exercise, but to practice moderation, say O'Keefe and Carl "Chip" Lavie, MD, medical director of cardiac rehabilitation and preventive care at Ochsner Health System, New Orleans. Lavie was involved in both the review and the running study.
"What we don't want to lose sight of is: People who exercise do better than people who don't exercise," Lavie says.
Endurance Training: Research Update
Evidence about the ill effects of chronic training for extreme endurance events is accumulating, the researchers say in the review.
An evolving body of data indicates that chronic training for, and participation in, extreme endurance events ''can cause dilation and stretching of the heart's chambers, especially the atria and right ventricle," O'Keefe says.
The pumping ability of the right ventricle can be reduced. Blood indicators that reflect damage to the heart muscle can increase, he says.
These changes usually return to normal, he says, within about a week. However, if the training is chronic, it may lead to scarring, enlargement, and stiffening of the heart, he says.
In one of several studies cited in the review, researchers compared 102 healthy male runners, aged 50 to 72, to 102 men who did not run. Each runner had done at least five marathons in the last three years.
About 12% of the marathon runners had heart scarring. It was three times more common in them than in the comparison group.
In the condition, the heart becomes enlarged, thick, or rigid.
Runners and Death Risk Study
For the running study, the researchers tracked nearly 53,000 men and women enrolled in the Aerobics Center Longitudinal Study. Each had a medical exam at the Cooper Clinic in Dallas in the years 1971-2002.
About 27% were runners. They reported how often they ran, how fast, and how many days per week.
The follow-up period varied, but averaged 15 years.
During that time, runners overall had a 19% lower risk of dying from any cause compared to non-runners.
A lower risk of death from any cause was found for runners who:
- Ran less than 20 miles a week
- Ran at speeds of six to seven miles an hour (about a 10-minute mile)
- Ran two to five days a week
Those who ran more miles a week at faster paces, or on more days than five, did not have any additional survival benefits, Lavie found.
The study was funded by the National Institutes of Health and an unrestricted research grant from the Coca-Cola Company.
Exercise Studies: Perspectives
Although a number of studies have focused on heart problems among endurance athletes, it does not prove cause and effect, says Aaron Baggish, MD, associate director of the Cardiovascular Performance Program at Massachusetts General Hospital.
"It's been known for decades these people [who train chronically for endurance events] aren't immune to heart problems," he says. "Whether the exercise causes the heart problems isn't yet known."
The athletes studied represent a small subset of people who push the envelope above recommended levels, he tells WebMD.
Baggish reviewed the findings for WebMD.
His research, published earlier this year in The New England Journal of Medicine, found that the risk of cardiac arrest during long-distance races is relatively low and often tied to pre-existing conditions.
Over a decade, he reported, one in 184,000 participants in full or half marathons had a cardiac arrest. Those who run a full marathon are at higher risk.
Endurance athletes who train chronically for competitions should ''have ongoing discussions with their physician about their health and take symptoms seriously," Baggish says
High-endurance exercise, done chronically, may come with a price, says Ravi Dave, MD, a cardiologist at UCLA Medical Center, Santa Monica. He also reviewed the findings.
"Everything in life, whether taking vitamin C, eating bananas, or exercising, has safe upper-dose limits," Dave says.
He says he probably won't discourage those who want to run a half or full marathon once or twice a year from doing so, if they are in shape and training for it.
"I'm more concerned about those who do very frequent high-endurance training for long periods of time, like the Ironman. Those are the ones I worry about," he says.
The percentage of people in the population who fit that description, he says, is very low.
Pay attention to intensity. You can take a leisurely all-day bike ride, he says.
"Even a century (100-mile) bike ride you can do safely if you don't hammer it." He encourages rest breaks.
Lavie concedes that some athletes love the competition and won't give up the long, grueling events. He encourages people to cross train, mixing in several forms of exercise.