Are marathoners running into heart trouble?

  • Article by: JEFF STRICKLER , Star Tribune
  • Updated: June 14, 2013 - 4:13 PM

Doctors now say marathoners might be putting their hearts at risk. But many long-distance athletes aren’t slowing down.

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Marathoning is booming, including this pack of runners in the Twin Cities Marathon.

Photo: GLEN STUBBE • Star Tribune 2010 file,

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Bill Wenmark has run 104 marathons and personally taught more than 4,000 first-time marathoners, with another class of graduates ready to lace up their running shoes for next weekend’s Grandma’s Marathon. He isn’t about to be scared away from either endeavor.

But Wenmark, founder of the Twin Cities-based ALARC running club, is watching with increasing angst as the medical community voices new concerns about marathon running — along with other so-called “extreme fitness” events such as Iron Man triathlons, boot-camp inspired obstacle courses and long-distance bike and ski racing. The concerns have nothing to do with joint and bone injuries.

Some doctors now say marathoning can cause heart damage.

The evidence is far from conclusive, causing Wenmark, and other experts to warn that the warning itself is potentially dangerous because it could be used as an excuse for not exercising.

“People who are anti-exercise are going to start with the ‘I told you sos,’ ” he said. “If you have someone who wants to run and a spouse who’s not supportive, you’re going to hear: ‘See, I told you so.’ ”

The worries about endurance exercising come as participation is booming. The number of marathoners jumped 50 percent between 2000 and 2010, according to figures gathered by Johns Hopkins University. While there are no statistics on how many of those marathoners also participate in other endurance sports, the turnout for other such events is surging.

And now it’s a different ilk of endurance athlete, said Dr. Bradley Bart, chief of cardiology medicine at Hennepin County Medical Center in Minneapolis.

“If we go back 10 years, the people running marathons trained ardently for that,” he said. “Now, with [endurance sports] becoming so popular, we’re seeing all these weekend warriors with much less training. They’re going to have a higher risk than a well-conditioned, well-trained person doing the same race.”

The reports raising questions about marathoning started appearing in medical journals last summer but have only recently caught the attention of the mainstream media, where headlines have been blaring. Take this one in the London Telegraph: “Too many marathons can kill.”

The research is not nearly that definitive. A study published in the journal Mayo Clinic Proceedings cited “emerging data” suggesting that long-term endurance exercise “may induce” cardiovascular irregularities. In a nutshell, the study said that endurance athletes experience temporary changes in their hearts that, in most cases, return to normal within a week of the race. However, for a few of the racers, permanent scarring, irregular heartbeats and calcium build-ups occur.

The report, which was not prepared by Mayo personnel, included a major caveat in its opening paragraph. “This concept is still hypothetical and there is some inconsistency in the reported findings,” the authors said. “Furthermore, lifelong vigorous exercisers generally have low mortality rates and excellent [cardiovascular] functional capacity.”

Dr. Tom Allison, director of sports testing and sports cardiology at the Mayo Clinic, said the studies are intriguing but not definitive.

“They’re based on observational data, and studies based on observational data always have their issues,” he said. “We’re still missing that large, randomized study that follows people for 10 or 15 years.”

The heart of the issue

Allison, who was a nationally ranked marathoner as a young man, said that the studies make sense from a theoretical standpoint.

“A typical heart pumps five liters of blood a minute when you’re at rest,” he said. “When you exercise hard, it will pump 15 to 20 liters a minute, and the heart stretches to accommodate the increased volume. But it’s reversible. When you slow down, the volume decreases. And once you stop, it returns to normal.”

He added: “If you do this for long periods of time — two, three or four hours straight — for 20 years, there’s a chance that the change in the structure of the heart could become permanent.”

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