Warning: before you attempt this year's trendiest workout, you may have to sign a death waiver.

Adventure racing is the one of the fastest growing outdoor sports--and at times--the most painful. Barbed wire, ice-cold dipping pools, or maybe even 100-miles of rugged terrain with little more than a compass for navigation serve as obstacles in a growing number of team races designed for both triathletes and amateur goofballs alike.



Extreme obstacle course marathons are "the next big thing," according to everyone from Outdoor Magazine to Forbes.



Troy Farrar, president of the USARA, the governing body of adventure racing, has seen "tremendous growth" in participation in the sport since 2010.

Originally designed for 'Iron Men' types and your run-of-the-mill Navy Seals, teams of 3 or 4 would navigate 100 miles of rugged mountain terrain by boat, rope and bike for up to three days. In the past two years, however, courses have been modified for amateur dare-devils. Instead of 100 miles, it may be 10. And instead of mountain climbing, it's a wall with a mud pit at the base. Some teams take their sport seriously, while others dress like Smurfs on acid and brave more mental challenges. Think memorizing the names of every US president after hauling a sack full of rocks.



Another reason for the growth in popularity: co-ed teams. "There's a social scene with it," Farrar tells Shine. "They train together, they go and race and afterward they camp out and party together."

Adventure racing teams have spawned relationships, and in some cases marriages. "I produced an urban adventure race in Houston," recalls Farrar. "One of the guys on the field proposed right before they took off racing. "

The sport is still largely male-dominated ("Alpha-male" dominated, if you ask the New York Times). Farrar estimates 75% of co-ed teams are guys. But don't count the women out.

"The girls of adventure racing are hammers," says Farrar, point to Robyn Benicasa, one of the top ranked racers, who doubles as a San Diego firefighter in her free time. "I think women are much better sufferers," says Farrar. "In general I think men complain when things aren't going so well. "

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And in adventure racing, things don't usually go well. In the past few years, courses have gotten off-the-wall bizarre.



At Spartan Races, one of the most popular new racing events, participants crawl under barb wire, launch spears into the air, hault sacks of stones and traverse greased up inclines at their own risk. The Tough Mudder races, which involve 10 to 12 mile courses packed with mud pools, high-voltage electric wires and freezing cold ice baths, require that aforementioned death waiver, absolving the organizers should the worst come to pass.

At a 2011 Tough Mudder event in Wisconsin, twenty-one participants finished the race at the hospital.

"We had people with orthopedic issues such as fractures to their arms or legs. Some suffered from dehydration. We had one person with a cardiac complaint," Kari Hall, director of emergency room services and urgent care at Sauk Prairie Memorial Hospital told a local reporter after the event. "That was just Saturday, but on Sunday we took five more Tough Mudder patients with some of the same type of injuries - fractures, dislocations and dehydration."

In the past, event organizers have come under fire for lack of safety measures. Spartan, Tough Mudder and similar "torture" races provide on-site medical assistance, and the USARA has been instrumental applying more stringent safety measures in outdoor courses. (For example, if you're scaling a mountain, you've got to wear the proper helmet now. This wasn't always the case, according to Farrar.)

"In most races someone's going to get a little scrape here or there," says Farrar. "But serious injuries are not really very common. "

Anyway, pain is part of the game.

Tami Collingwood, 40, a veteran half-marathon runner twisted her ankle while climbing over an 8 foot wall during a race called The Ruckus in Pittsburgh. She still finished the course, ankle be damned.

"You get kind of addicted," she told the Pittsburgh-Post Gazette. "It's like an adrenaline rush."



