Matt Sands/US Road Sports & Entertainment, via Karhu

This is a story about men who race in bear suits.

Since 2011, at least a dozen men have run a 5K while wearing a bear suit in the United States and an additional five have done it in Europe. They have run in Miami, Chicago, Dallas and Fort Lauderdale, Fla., and while a bear is expected to make an appearance in the lead-up to the New York City Marathon this year, he is not expected to tackle the 26.2 miles of the course. He may appear on the trails at Central Park, and one can only hope he will provide New York’s resident sad panda with some company, if not a training companion.

Like so many trends in running, the furry brown bear, with its prominent teeth and somewhat crossed eyes, is tied to a shoe company promotion. In this case, it’s Karhu, a Finnish sports brand that has recruited competitive yet casual athletes who are trying to add a new wrinkle to their middle- and long-distance-running résumés and partake in some non-Halloween dressing-up. They track their times and compare notes on how to handle the sweat under the fur, but leave some onlookers baffled.

The battle for shoe endorsement real estate at major races and track and field events is a competitive one. Nike owned the United States Olympic track and field team trials in Eugene, Ore., but that did not stop Brooks from banner-bombing high above Hayward Field. The London Games belonged to Adidas. Asics and Foot Locker are New York City Marathon sponsors. (There’s also the potential risk of the Karhu bear running against specific sponsorship rules for runners.)

Karhu uses a bear as its logo and is trying to expand its share of the United States sneaker market; it provides the man-bears with some of the company’s shoes and apparel for volunteering to wear the costume. The runners are found through a network of friends and shoe dealers across the country and they may also make nonrunning-related appearances.

The tradition of running in costume is far from new. In the 1980s, the New York City Marathon had Roger Bourban, the running waiter, who, clad in a tuxedo, carried a tray and an open bottle of Champagne and set record times. There are runners dressed as Scrabble tiles, toasters, Mr. Peanut, faucets, hot dogs and frogs at the Tokyo Marathon and as a whoopee cushion in London.

It is not easy being a bear.

“It’s kind of like running with a bunch of carpet on,” Matthew Blume, 31, of Chicago, said. Blume achieved what is believed to be the current bear-suit world record time — 18 minutes 25 seconds — in a 5K at the Chicago Half Marathon event last month. That is about three minutes slower than his best 5K time, he said. But he is not your average bear. In general, the runners in the bear suits finish their 5Ks with times from 19:30 to 20:30, with the suit adding a solid minute per mile to a bear’s finish compared with a noncostumed time, organizers said.

Blume said he first heard about the promotion through a local shoe store.

“I normally don’t run in a bear suit,” he said. “It just seemed like a fun thing to do. I’m competitive and it seemed like a new challenge.”

In addition to the oppressive heat inside the 10-pound suit, visibility with the heavy bear head is also limited to a small window out of the animal’s mouth. The bears are assisted by guide runners, and medical staff is on hand. Hydration before the race is strongly encouraged.

“Your visibility is almost nil,” Blume said. “My training partners would say, ‘Watch out for this curve,’ and things like that. If I didn’t have them, I would have been in big trouble.”

The bear suit includes gloves that come off, but wearing a stopwatch is petty much out of the question. That’s one of several reasons, the bear runners said, running a marathon or half-marathon in a full bear suit is close to impossible.

Even at the finish line of a 5K, Bill Moss, who is based in Marietta, Ga., and raced in a bear costume for the third time recently in Atlanta, said he chucks off the head and gloves as fast as he can.

Which raises the question of why Moss wore a bear suit even once, let alone three times.

“It’s fun!” Moss, a 30-year-old chiropractor, said.

But it can be bittersweet when he is passed while wearing a costume, Moss said. “They pat me on the back and say, ‘Good job, bear.’ ”

Some tactics for running in the gear include carrying the head instead of wearing it, taking off the gloves, and even splashing one’s face with the mask on, hoping that some of the water makes its way in. Many bear runners dress in shorts and a tank top as a feeble fight against the inevitable heat.

“It can get claustrophobic in there,” Moss said. “It’s like wearing a gigantic furry diaper when you run.”

After a race, the brown coat is sweat-soaked and has a putrid odor, the runners said. (The company said it picks up the cost for dry cleaning the suit between races.) “It’s disgusting,” Moss said.

But the bear racing experience has greatly increased his sympathy for mascots in other sports, Moss said.

“I hope that they’re paid very, very well,” he said.