How are ultra-runners able to persist through long, exhausting miles of running? It may be because these athletes experience less pain than the average person, according to new research from Monash University in Australia.

The researchers compared several self-report pain measures of 19 ultra-runners and 9 non-ultra runners, and had them complete a pain-inducing experiment, known as a Cold Pressor Task.

Read: Runners Lose 6% Of Their Brain Size During An Ultramarathon, Research Finds​

During the Cold Pressor Task, participants submerged their arm in icy water for up to 3 minutes, and were asked to report their pain on a 11-point scale every 10 seconds. Overall, the ultra-runners were able to bear the cold longer than their counterparts.

"What we found in this preliminary study is that ultra-runners had reduced pain ‘attention’ and may think about pain in a distinct way from the rest of the population," said lead researcher Bernadette Fitzgibbon, in a news release.

Fitzgibbon's colleague and study co-author, Donna Urquhart, competes in ultra marathons, which include any running event longer than the traditional 42 kilometers (26.2 miles) marathon.

“Originally I would start feeling pain at the 40km mark and it would intensify through to the 100km mark, but as my runs got longer and longer, I learned it doesn’t get any worse,” Urquhart told The Sydney Morning Herald.

The research will be presented at the Australian Pain Society's annual general meeting.

In the future, Fitzgibbon wants to look at ultra-runners’ personality type. The majority are white collar, middle aged, and successful, she notes.

“Surprisingly they don’t seem to be hyper competitive, but are certainly highly motivated and goal oriented,” said Fitzgibbon.

Ultramarathons are becoming increasingly popular. Common race distances are 50 and 100 miles and 50 and 100 kilometers, or 31 and 62 miles.

See also: Is Running A Marathon Bad For Your Body? Physical Stress From Long-Distance Running May Damage Kidneys​

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