In this June 17, 2012 photo, Kaitlin Karalunas of Pittston comes down the home stretch of the Warrior Dash at Pocono Raceway in Long Pond, Pa. Virtually overnight, obstacle courses have become a favorite diversion of thrill-seekers and weekend warriors. (AP Photo/Scranton Times & Tribune, Melissa Evanko)

MICHAEL RUBINKAM

LONG POND, Pa. (AP) - More than 10,000 people trekked to northeastern Pennsylvania to scale walls, leap fire and crawl commando-style through a mud pit topped with barbed wire.

Willingly. For kicks. And they paid money to do it.

That's obstacle course racing for you: grueling, mud-spattered and, to its legions of fans, addictive fun.

In only a few years, obstacle courses have become a favorite diversion of thrill-seekers and weekend warriors, with hundreds of events around the country that require participants to go up, over, under and through to the finish line.

Three of the top series - Tough Mudder, Warrior Dash and Spartan Race - expect to host nearly 2 million runners in 2012, from fitness buffs bored with straight-line running to pasty 9-to-5ers blowing off steam with friends, from adrenaline junkies pushing the limits of their own physical and mental endurance to couch potatoes for whom working the remote more typically qualifies as exercise.

"I felt like a kid again for the first time in I don't know how long," says Hobie Call, 35, a former air-conditioning technician from South Jordan, Utah.

Call was a world-class marathon runner looking for something new when his wife urged him to enter an obstacle course race. He was doubtful - "I don't care about getting muddy," he told her - but he took to it immediately, going on to win 21 races in his first 16 months.

"The people who dare do it, they do it and they're hooked for life, and sign up for five more," says Call, who's quit his day job to devote himself full-time to the emerging sport. "That's why they are exploding in popularity."

That was evident on a recent weekend in northeastern Pennsylvania, where Warrior Dash - the 2-year-old creation of Chicago-based event planning company Red Frog Events - set up a course around the perimeter of Pocono Raceway. Each half hour, another wave of racers took off from a starting gate rigged with pyrotechnics, then negotiated obstacles that required them to walk planks, crawl under brush, scale steep walls and scramble over cargo nets on their way to impediments named Warrior Roast and Muddy Mayhem, the big fire-and-mud finish.

Doesn't exactly sound like your idea of a good time? Tina Lengle wasn't so sure either. But the 33-year-old stay-at-home mom from Hershey joined a couple college friends and ran the 3.1-mile course in just over an hour.

"You gotta do something fun in your life. Life's too short," Lengle said triumphantly a few minutes after crossing the finish line, her body caked in drying mud.

She said finishing the race made her feel empowered: "You can do anything. You're strong."

The best of the runners completed the course in just over 20 minutes, barely visible under a layer of mud and grime as they received their medals. But winning was really beside the point. For the vast majority, finishing was its own reward.

That's because Warrior Dash is basically a giant party - think live bands, copious amounts of beer, and free turkey legs - built around a 5K obstacle course. And it doesn't take itself too seriously, inviting racers to show up in costume, the crazier the better. At the Poconos race there were three Ghostbusters - wearing tan jumpsuits and proton packs, natch - two video-game characters (Nintendo's Mario and Luigi), and a young man in a Spartan getup. (Wrong race, fella.) On the opposite end of the competitiveness spectrum is the Spartan itself, a popular series whose founder is pushing to make obstacle course racing an Olympic sport, and whose pinnacle event is a 48-hour slog called Death Race, in which 90 percent of the few hundred who enter each year fail to finish. Spartan doesn't give racers any advance warning about what they might encounter, saying only there is "fire, mud, water, barbed wire, and occasionally Hell on Earth. There WILL be obstacles to catch you off guard."

Tough Mudder, meanwhile, says it's not a race at all, but a challenge. Runners must pledge to put teamwork and camaraderie ahead of their course time as they negotiate a 10- to 12-mile course with obstacles like Arctic Enema - a swim through ice - and Electric Eel, which forces you to slide on your belly while avoiding live wires. Zap!

The races are certainly a novelty, and most novelties eventually wear off. But organizers insist they've tapped into something deeper, more primitive and elemental.

"Humans have done this for 900,000 years. We didn't go to Starbucks. We went out and hunted food," says Joe Desena, co-founder of Spartan Race. "When we put people in this environment, they feel at home because deep down inside this is what we did for so long."

Alex Patterson at Tough Mudder says that in a world in which "we're never too cold, we're never too hot, everything is just right," people long for a challenge - and a unique experience.

"We are tapping into the idea of experiences as a new luxury good," he says. "You are often advertising who you are through Facebook, and the photos you post on Facebook after the weekend. Think about what you can say at the water cooler the day after. You can spend all day Monday talking about your experience, and people do."

As with any physical activity, there's always the risk of injury, or worse. Two men collapsed in the heat and died while running a Warrior Dash in Kansas City, Mo., last year. And three people developed E. coli infections after running a Tough Mudder event in Scotland last month, according to the Scottish health agency. Investigators are working to confirm a link, according to Tough Mudder spokeswoman Jane Di Leo.

"Hundreds of thousands of people have gone through our courses without a problem. This is the first time that anything like this has ever come up," she said.

Di Leo and officials from other companies say that runners' safety is paramount, with water and first-aid stations positioned along the courses and all applicable laws and health regulations complied with.

Ray and Kate Meehan, a married couple from Philadelphia, did Warrior Dash together and considered it a milestone along their journey to better health.

"I tell my son he can do anything he puts his mind to," said Ray Meehan, 48, who's lost 50 pounds. "I figure if I tell that to him, I better try this."