Most marathoners worry about hitting the wall – losing steam late in the race. But on Nov. 22, racers in Churchill, Man., face an even bigger fear: running into a polar bear.

The 13 runners follow a flat, exposed and winding 42-kilometre course along the icy coast of Hudson Bay. Local volunteers will drive beside them, carrying food, water, clothing and loaded guns. The runners are coming from Canada, the United States and Europe as well as Churchill. They will face icy winds, snow and extreme cold. The predicted high for Friday is -20 C, but the windchill is - 41 C.

"We'll wear more three, four, maybe five layers," says ultra marathon runner Albert Martens of Steinbach, Man., who started the event last year. Martens, 65, is a veteran of 48 marathons and more than 10 ultramarathons, including the 217 km Badwater Ultra in Death Valley, Calif., which is known as the toughest footrace on earth.

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Last year's Polar Bear Marathon attracted runners from Canada, the U.S. and two from Germany. Mike Pierce of San Diego had a unique way of preparing for the run: He trained in a commercial freezer. The first group to cross the finish line was Eric Alexander of Vail, Colo., an experienced mountaineer who escorted the first blind mountain climber to the summit of Mount Everest, and Gary Koop, a pastor from Steinbach.

In the end, the runners' most fearsome opponent wasn't polar bears. It was the weather. Though the marathon started in mild conditions with temperatures at -10 C, the Arctic soon bared it's teeth, bringing snow, strong winds and numbing cold. None of the runners had encountered a polar bear. However, a local guide did scare off one bear that had gotten too close to the road with a noisy "cracker" shell.

Martens, who crossed the finish line in just over six hours last year (roughly two hours behind the winners), says recent bear attacks in Churchill don't worry him. "We really rely on the locals to keep an eye out for us," he says.

Aside from bragging rights, participants in this year's Polar Bear Marathon will receive soapstone carvings from a local First Nations artist.

With a report from Catherine Dawson March

Special to The Globe and Mail, with a report from Catherine Dawson March