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Ultrarunners aren't always ultrahealthy

One of the first large scale studies of ultrarunners -- those who race distances longer than the standard 26.2-mile marathon -- shows that these runners are overall very healthy, but tend to suffer from more knee pain, stress fractures, allergies and asthma than the general population.LUCY NICHOLSON / Reuters

One of the first large-scale studies of ultrarunners -- those superhumans who race distances longer than the standard 26.2-mile marathon -- shows that these runners are more likely to suffer from more allergies and asthma. 

They also report more knee pain and stress fractures, but when you're running 50 miles at a time, that seems about right.

Like marathons, the number of people participating in ultramarathons has rapidly increased. In 1998, about 15,500 runners had finished ultradistance races; in 2012, that number jumped to 63,530, according to Ultrarunning Magazine. But despite the popularity of ultramarathons, we don't have a lot of good data on the health of these runners. 

“Exercise is good, we all know that. But how much exercise is too much exercise? Is there such a thing as too much exercise? We don’t know,” says Eswar Krishnan, assistant professor of medicine at the Stanford University School of Medicine. Krishnan co-authored the paper, published in PLOS ONE, with Dr. Martin Hoffman, a professor of physican medicine and rehabilitation at the University of California, Davis. 

Researchers analyzed surveys from more than 1,200 ultrarunners, and they plan to follow these runners for the next two decades. So far, their findings suggest that, overall, ultrarunners are a healthy bunch: In a year, they'd taken about two sick days, compared to the four that most Americans miss each year. 

But many reported knee pain, and about one in 20 of the runners reported a stress fracture in the past year. And while about 8 percent of Americans have allergies or asthma, 11 percent of these ultrarunners reported asthma, and 25 percent reported allergies. Krishnan says this is likely because they're spending more time outside than most of us. “We are all potentially allergic to many things, but we don’t see symptoms because we don’t come into contact with these allergens,” he says.

Up next: The ultrarunners have just been sent a survey probing the psychology of ultrarunning, which means we're soon going to find out what on earth drives these people run 30, 50, even 100 miles at a time.