"We have anywhere from 3,000 racers to 10,000 per race and they consist of a wide variety of people," says Jeremy Benoit, spokesman for Spartan Race. (The larger number is projected for the Tri-State edition of the race.) "A large number are either military or students, and the remainder are everyday people that have a knack for fitness and pushing their limits." Those participants are also extremely loyal. Scores of Tough Mudder, Spartan Race and Warrior Dash badges show up in Facebook profile pictures before each race. Runners recruit friends from their walls. When it's all over, participants often get another badge to show they've completed the event. Both Warrior Dash and Spartan Race have around 800,000 friends on Facebook. Tough Mudder not only has nearly 2 million friends, but proudly proclaims in press releases and interviews that more than 1,000 participants have had the Tough Mudder logo tattooed somewhere on their person. "There are a couple of people, and I ran into one a couple of weeks ago, who have the Tough Mudder pledge tattooed across their entire back," Patterson says. "We've really tapped into something here bigger than just the company." Corporate sponsors have taken notice. Tough Mudder counts UnderArmor ( UA), Unilever ( UN) and Clif among its partners, while Warrior Dash has Molson Coors ( TAP) and Monster Energy ( MNST) helping it over the finish line. It helps that a bit of their proceeds go to charitable organizations as well. Tough Mudder has donated $2.5 million to the Wounded Warrior Project and has invited veterans with post-traumatic stress disorder and physical injuries to take part in the event. Spartan Race also acknowledged its military training roots this year by partnering with Homes For Our Troops, which provides housing for veterans who have been severely injured while on duty. Warrior Dash takes on two charities by allocating up to $1 million to St. Jude's Children's Hospital and donating muddy sneakers to GreenSneakers, an organization that sent nearly 180,000 pairs of cleaned and restored sneakers to recipients around the world in 2011. "There are people who are afraid of our event who I look up and down and say 'Look, I know you probably think that you can't do this course and that it's not for me and I've never run 10 miles in my life,'" Tough Mudder's Patterson says. "It's a marketing challenge to say 'It will kick your expletive ,' but it is doable if you train and have the right mentality.'" -- Written by Jason Notte in Boston. >To contact the writer of this article, click here: Jason Notte. >To follow the writer on Twitter, go to http://twitter.com/notteham. >To submit a news tip, send an email to: firstname.lastname@example.org.