In a few days, Greg Ripley will be inching under barbed wire, climbing up cargo nets, clambering over junked cars and leaping through a pit of fire.

His training for this weekend's Warrior Dash has been a little more sedate: pushing his 6-month-old daughter's stroller during uphill runs.

Ripley, 38, of Minneapolis, is one of thousands of weekend athletes signing up for these boundary-pushing, ego-boosting events that are gaining popularity worldwide and have exploded in the Twin Cities area this summer. The races provide not just fitness challenges but all-out music festivals with spectators, food and costumes.

"I thought, what the heck?" Ripley said. "It looked crazy and fun -- and I heard there's beer at the end."

Called adventure racing, mud runs or obstacle course races, the events draw a mix of people -- gym fiends who are bored with their own workout routines, newbies who like the teamwork aspect of the events and thrill-seekers who want to star in their own version of TV's "Survivor."

"We like to push ourselves. It's our desire to reach our full potential as humans," said Greg Chertok, director of sports and exercise psychology at the Physical Medicine and Rehabilitation Center in Englewood, N.J.

A sense of accomplishment improves a person's mental health, especially when the completed task is perceived as particularly challenging or even impossible. "That sense of achievement is like a drug," he said. "It's addicting."

Pam O'Brien, executive editor of Fitness magazine, said that runners get bored with the smooth terrain and time-centered competitive atmosphere of an average 5K or triathlon. "Workouts can get old fast. You need to switch it up and do different things to make it fun. It's the anti-boredom factor."

The obstacle course-like races have been wildly popular, often drawing men and women equally.

Ripley is one of nearly 24,000 running in this weekend's Minnesota Warrior Dash, a 5K race organizers describe as a "mud-crawling, fire-leaping, extreme run from hell."

The dash is held in 30 other locations throughout North America and Australia and is stopping in Minnesota for the first time Saturday and Sunday at Afton Alps near Hastings.

A similar event called Go Commando started the string of Twin Cities events in June, followed by this weekend's Warrior Dash. Next up: the Rugged Maniac and Muddy Buddy in August, the Mud Run MS Twin Cities in September and the Tough Mudder, coming in 2012.

The races fall on a spectrum of difficulty level and cost, lengths varying from 3 miles to 10-plus miles, with registration fees between $50 and $180 per participant (which sometimes includes a beer or a souvenir).

Partiers often dress up, trying on another persona.

"I've seen everything from superheroes to ... warriors, avatars, [characters from the movie] 'Caddyshack' and Smurfs," said Muddy Buddy founder Bob Babbitt.

'Survivor' for everyone

The events have varied origins. Paul Courtaway, co-founder of the oldest local mud event, the Mud Run MS Twin Cities, began the race in California in 1990, when he and fellow members of the U.S. Marine Corps saw how much their families wanted to play on the military obstacle courses.

"It's the definition of American spirit. You can call it 'warrior,' 'tough' or 'Spartan' but the bottom line is [event participants are] doing all the things associated with the military," he said, stressing that Americans like to emulate soldiers.

Another race that's been around since the 1990s, the Columbia Muddy Buddy, was first held near San Diego in 1999. Babbitt said these events, often called "Survivor"-style, have origins linked to the popular TV show.

Mark Burnett, creator of "Survivor," first started "Eco-Challenge: The Expedition Race" in 1995, a multi-day 300-mile trek with challenges like kayaking, horseback riding and scuba diving. That race-turned-TV-show premiered on CBS as "Survivor" in 2000.

Adventure races like the Mud Run MS Twin Cities and Muddy Buddy were a way for average athletes -- or just adventurous souls -- to get involved in the craze. Babbitt said he watched the popularity of the races grow as "Survivor" and similar shows, like "Amazing Race," popped up on America's television screens.

"I started [Muddy Buddy] because people get bored," he said.

Why Minnesota, why now?

While Go Commando, Muddy Buddy and the Mud Run MS Twin Cities are in their second year locally, the others are making their Minnesota debut. One explanation for this mud rush, Courtaway said, is that these organizations are competing with each other, so when one has success in a new location, the others follow.

"The region has a great appreciation for the outdoors and a large community of fitness enthusiasts and runners," said Will Dean, CEO of Tough Mudder, the longest of the events with a 10-mile-plus trek. It will be held in a to-be-announced Minnesota location  next June.

Courtaway said that for his company, it was about the land. "Minnesota has ski resorts that aren't really mountains but have really treacherous terrain," he said.

Risky business

Videos and photos from several of the events show runners leaping off 7-foot climbing walls, flames crawling up their legs and mud encrusted on their bodies and faces. One video shows a participant being carried away on a stretcher.

William Roberts, a University of Minnesota professor and former president of the American College of Sports Medicine, said the risk of injury is high, especially for the untrained athlete.

Doctors' orders: Leave the beer-guzzling for after crossing the finish line, and get your body in shape before race day.

"Go in with a clear head and the idea more of having fun than doing it real fast," he said.

Teamwork and mud

Adventure aside, many runners just want to team up and get muddy.

Jason Meyer, 37, said he's looking forward to building camaraderie at the Warrior Dash, an event he's running with co-workers from a small Minneapolis IT consulting firm, Ratchet. Thirty-three of Ratchet's 35 employees are committed to the race.

"It makes it more fun because you're supporting each other," he said.

Pamela Enz, 58, of Minneapolis, got dirty in the Mud Run MS Twin Cities last year, and is coming back for more with the Warrior Dash.

She remembers her experience fondly.

"It took us three days to get all the mud off ourselves or to get the stench off because we smelled so bad," she said, laughing. "Doesn't that sound insane?"

For O'Brien, the Fitness magazine editor, it's not at all crazy.

“When you’re a kid, you're allowed to get dirty, but when you're an adult you're too old to do that,” she said. “When else do you get to roll around in the mud?”

Jessica Bakeman • 612-673-4401