It’s hard for many people to imagine running (or walking) a standard marathon of 26.2 miles, let alone topping that distance with a so-called ultramarathon that could stretch to as much as 100 miles or more. And researchers still know very little about what such grueling treks can do to the human body.

A new health dispatch from a study that followed more than 1000 ultramarathoners from 2011 to 2012 sheds a bit of light on the issue, suggesting that those extensive runs may not be all that damaging to the body – at least, not for the sliver of the population that chooses to take on such feats. But don’t grab your running shoes and marathon GU just yet. The runners included in the study had been doing ultramarathons for fewer than six years on average. That means we still don’t know about the long-term wear-and-tear of such runs. The findings are published on January 8 in PLOS ONE.

The results, which come from the fittingly named ULTRA (Ultrarunners Longitudinal TRAcking) Study, include the health data and running experiences of 1212 ultramarathon runners who had recently completed an ultramarathon. Of that total, 933 reported some exercise-related injury in the past year. Of those runners, 783 (64.6 percent) say their injuries resulted in loss of at least one day of training. The median loss was 14 days.

Not surprisingly, the study finds that ultra-runners are healthier than the general population. More experienced runners were also less likely to suffer injuries—such as broken bones—than slightly younger, inexperienced ultramarathoners. On average, uninjured runners had been doing ultras for seven years and were around 45 years old while injured runners had been doing ultras for five years and were around 42 years old. Adaptations including modifying running speed, intensity and the way the foot strikes the ground may all be factors that help protect against injury, the authors write.

Among runners over 45 years old, 47.4 percent remained free of injuries while 38.4 percent were injured, says study author Eswar Krishan, a professor at Stanford University School of Medicine.

As happens in other types of running, most ultramarathoner injuries were to the knee. Compared with shorter distance runners, ultramarathon runners suffered more stress fractures in their feet (perhaps from running on the uneven terrain), and compared to the general population, ultramarathoners had more symptoms of allergies and asthma (which may make sense since these runners would spend so much time outside). Stress fractures were also more common among women than men.

There are a couple drawbacks to this study. The population that chose to respond to the emails and online postings about the survey may also be somewhat different from the ultramarathon population at large and so does not necessarily tell us about all such runners. Plus, the health data was all self-reported, so it’s possible that runners may have fibbed about their injuries or training regime (though the investigators tried to check for any such glaring inconsistencies, like, say, if a runner reported a severe injury but then did not miss a single day of training).

The work does not assess if there are any differences between the ultramarathoners in terms of their equipment or how they prepared to avoid dehydration, frost bite or other injuries related to exposure. The study does not make a distinction between the length of various ultramarathons so we don’t know if runners may be getting more injured after, say, the 56-mile mark or after 27 miles.

A tricky part of uncovering better data on the health impacts of such lengthy runs is finding a good comparison group for such long-distance runners. Considering such a tiny chunk of the population participates in ultramarathons it’s not ideal to compare them to the whole U.S. population. Comparing them to professional athletes, military members or regular exercisers might be a better fit, says Krishnan, but no one group is a perfect match so it may make sense to compare to each of them.

Though the study may leave a reader wanting more information it does whet the appetite for future reports from study. I’ll be keeping a close tab on what the researchers uncover in the coming years. Still, no matter the findings, I think I’ll stick to running around the block.