Most marketers wouldn’t want to have their names dragged through the mud.

But not some brands.

After years of prodigious growth, “mudventure” obstacle racing has oozed into the mainstream, with top brands like Reebok, Miller Lite and Advil jumping in. The sport, which barely existed five years ago, fuses strenuous, often punishing and on occasion even death-defying physical activity with team dynamics, social interaction and the meeting of tough challenges head on. And along the way, participants get as filthy as if playing in a pickup football game in a driving rainstorm.

Winning is not the objective here. In fact, many events don’t even track the times of the entrants. Rather, personal achievement and having a good time with friends and family are key. And while some serious athletes take part, the category’s success and its growing attraction for brands have more to do with the enthusiastic participation of the average person, testing his or her physical limits and sharing the experience with others.

“While most people will never play NFL football, nearly anyone can participate in these action-adventure competitions, and participants in these events respect and support their sponsors,” says Darryl Ohrt, global creative director at content firm Mash+Studio and a prominent marketing blogger.

There’s big money in mud. Last year, the big three mudventure series—Tough Mudder, Spartan Race and Warrior Dash, which together hosted some 2 million participants—generated an estimated $200 million. When smaller races are factored in, the overall market could well rake in twice that much, according to experts, and this year could reach $1 billion and draw as many as 4 million participants worldwide.

Regardless of size, location or level of difficulty, the events (for which participants pay anywhere from $50 to $200) are known for activities like scaling walls, wading through pools of slime, crawling through pits of barbed wire and, in one case, dodging live electrical cables. As the name suggests, there’s always plenty of mud involved, and post-race parties.

On-site brand activations, signage and co-branded merchandise are fast becoming a part of the mix, too. The benefit for marketers is clear, as mudventure events attract demos brands crave. Participants generally fall into the 18-40 sweet spot, with an average household income in the $70,000 range. Some event series, including Tough Mudder, are male-oriented (the split is about 70/30), but the events are attracting more women. (There’s a female-only series called Dirty Girl.)

Meanwhile, for the participants who have made mudventure such a hot ticket, the events tap into our collective desire to escape, if only for a weekend, the shackles of buttoned-down, mechanized society.

“We feel cooped-up in our cities where hand sanitizer is everywhere,” says marketing blogger and pop culture pundit Ask Wappling. “We want to run barefoot with our feet in the mud like we did when we were kids. We want to push ourselves and see how far, how fast, how sweaty we can get. We want to laugh, scrape our knees and win.”

It also feeds into our social media-centric lifestyles. “A Facebook photo of yourself competing in a mud run is the ultimate humble-brag. It clearly shows that you’re fit, fun and adventurous. And since you’re covered in mud, the pic has a tinge of self-deprecation too,” explains Jonathan Ages, founder and editor of Blood, Sweat and Cheers, a daily email that helps people discover activities to do with friends.

Adds Alex Patterson, chief culture officer at Tough Mudder: “Experiences are what people want these days. They don’t just want goods … now that everyone is their own content-generating brand.”

That content is all the more impressive when it involves activities so down and dirty and achievement-oriented as these. “It definitely showed me I can do things I didn’t think I could do—I didn’t think I could finish it,” says Chelsea Cutaran, 24, a nurse in a cardiac care unit. Entering for the first time with a group of co-workers, Cutaran completed a 10-mile Tough Mudder event last July at Big Bear Lake, Calif., in about five hours.

As with any sport or activity, there are dangers. Tough Mudder makes its entrants sign “death waivers,” just in case. (“It definitely gave me second thoughts, but I got over that quickly,” says Cutaran.) But mudventure has its own unique risks. For one thing, mud can contain harmful microorganisms—E. coli outbreaks at events from entrants ingesting mud aren’t unheard of. Then there are the obstacles themselves. Tough Mudder’s course includes such activities as Electric Eel, which requires participants to crawl through mud while 10,000-volt live wires dangle above; Arctic Enema, a pool filled with ice water in which participants must submerge themselves and navigate beneath a plank; and Funky Monkey, which involves an incline smeared with mud and butter and a set of monkey bars above a pit of icy water.

While the organizers stress that safety is their top concern, injuries are fairly common. Jennifer Anderson, 39—who, like Cutaran, is a nurse—broke her tailbone going down a Plexiglas slide at the Ruckus mud event in Marshfield, Mass., in June 2012.

“I know it wasn’t the course that did it to me—it was a freak accident,” she says. Anderson went on to complete another run five months later, and she plans a return to the Marshfield Ruckus this year. “I didn’t want to go out injured,” she says. “It all goes back to the accomplishment thing. As a mom of three, I don’t get a lot of things about me.”

“This definitely marks a shift from the identifying with Tiger Woods and Michael Jordan on the [Wheaties] box to people wanting to be on the box,” says Tough Mudder’s Patterson. (As it happens, Tough Mudder will grace a Wheaties box of its own later this year, according to Patterson—clearly marking mudventure’s move into the mainstream.)

Brands certainly are throwing big bucks at mudvertising opportunities. Backing several races at a major event series can cost a marketer anywhere from $500,000 to $1 million, while long-term deals can run into seven figures. Spartan Race’s three-year pact with Reebok is the most comprehensive sponsorship in the space. In fact, the event series is now called the Reebok Spartan Race and encompasses on-site activations, apparel, a line of running shoes, a mini-Spartan course at the marketer’s Canton, Mass., HQ and more. “We were really looking at how our brand is positioned in fitness—we really connected well with them,” says Chad Wittman, Reebok’s director, sports fitness entertainment marketing. “They’re all about transformation, [and] we believe in the same things.”

Reebok-Spartan athletic wear will hit retailers this summer, with a specialty footwear launch set for January 2014. Likely priced in the $150 range, the shoes will feature “new technologies,” says Wittman, based on the needs of mud runners to keep muck out of their sneakers—and keep the sneakers from coming off altogether.

For a lifestyle brand like Reebok, mud-venture is a natural complement because the events themselves can become a lifestyle, transforming people from couch potatoes into enthusiastic amateur athletes who enter several events a year. (It is estimated that one in four participants are repeat racers.) With that in mind, brands like Reebok aim to connect long term with consumers who integrate mudventure sports—and a commitment to exercise and fitness—into their everyday lives.

Other partners seem less obvious a fit. Take Dos Equis, a fixture at Tough Mudder, where each of those who completes the course gets a free brewski. MillerCoors made its foray into mud racing last year with Warrior Dash, returning as official beer sponsor this year. “Warrior Dash embodies Miller Lite’s positioning of fostering the bonds of friendship,” says the brewer’s spokesman Jonathan Stern. “Great friends come from far and near to participate in the Warrior Dash. Miller Lite is all about good times with good friends, so the two brands work well together.”

Not everyone likes the idea of beer brands waiting at the finish line with a cold one.

“Tough Mudder and Warrior Dash, although a step in the right direction, are not promoting fitness and athleticism … they are promoting a party,” argues Joe De Sena, co-founder of Spartan Race, adding such sponsorships denigrate the sport’s healthy-lifestyle positioning. And yet, if a brewer approached Spartan Race, De Sena doesn’t rule out accepting those dollars. “Depends on the terms,” he says.

Pfizer’s Advil, meanwhile, sees sponsoring Tough Mudder as a no-brainer. “Advil relieves tough pain. Event day puts stress on muscles, as does training, so it’s a really good fit for us and an organic partnership,” says Jody Cook, director of brand communications. This is the OTC remedy’s first year of sponsorship, which includes an eight-foot-high, branded obstacle wall and product sampling at a dozen events.

Despite the obvious value for a brand, the extreme nature of these events and the very real risks involved could spell trouble for a sponsor in the case of grievous injury or death. Two incidents that generated significant media attention are slated for trial this summer, at the height of mud-racing season. In April 2012, at an Original Mud Run in Fort Worth, Texas, 30-year-old Tony Weathers—by all accounts an elite, accomplished athlete—disappeared during a 150-foot swim across the Trinity River. The medical examiner ruled his death an accidental drowning. Weathers’ aunt filed a lawsuit, naming the organizers as plaintiffs. The trial is set to begin June 27. Meanwhile, Robert Fecteau, a veteran marathoner, last year filed a $30 million suit against the Filthy K Mud Run, alleging he became partially paralyzed after landing in a mud pit during a 2010 event in Richmond, Va. That trial begins July 15. (More recently, a participant drowned in a Tough Mudder event this past April, in what was ruled an accident.)

Marketers apparently accept the risks. “Brands need to stand for something and mean something for consumers,” says Advil’s Cook. Other brands Adweek spoke with concur, signaling that as long as organizers are seriously committed to safety, sponsors will be satisfied. What’s more, any negative publicity will impact the events themselves, they propose, not the sponsors—much like the NFL, not its advertisers, has come under fire for player injuries.

Besides, as Reebok’s Wittman points out, “More people die from heart disease and obesity than from being active.”

That said, would Reebok continue to support Spartan Race if a participant were to die and the story played out on CNN and Fox News—the brand’s logo appearing in every shot? “We stand behind our partners as long as it’s not foul play on their side or negligence,” Wittman says.

Adds Spartan’s De Sena: “To enjoy life, you’ve got to suffer every day. There’s certainly some danger here. I think sponsors can deal with the injury issue.”

That, and getting a little dirty.