- The Arrowhead 135 is a 135-mile endurance race through northern Minnesota.
- This year's race coincided with the polar vortex. Temperatures dipped to -32 Fahrenheit, with wind chills reaching -55.
- Organizers hope for some of the chilliest weather of the year when they pick the date of the annual race.
- Of the 146 people who attempted the race this year, just 52 finished.
During the polar vortex, when a blast of cold air rushed south from the Arctic, temperatures in Minnesota dipped to negative double-digits.
Most people took the bone-chilling temperatures - which can freeze skin in as little as five minutes - as a sign to stay indoors: mail service and school classes were canceled in several states.
But a rather unusual crew of experienced hikers, skiers, and bikers decided that this week, of all weeks, would be an excellent time to endure a 135-mile ultramarathon.
Starting out near the Canadian border on Monday, the endurance athletes pedaled, walked, ran, and skied the hilly trail between two towns that consistently record some of the coldest temperatures in the nation: International Falls and Tower, Minnesota.
This is the Arrowhead 135, an annual torture test of low temperatures that some people relish.
"They like the challenge," race volunteer Russ Loucks told Business Insider. "There's a good contingent of winter enthusiasts up here who just like doing things in the winter."
One veteran biker even broke a speed record this year.
Here's what the race looked like.