Adding obstacles normally keeps people away. But not when it comes to Metro Dash, which was originally a four-mile race scattered with functional fitness pit stops. For last year's events, one of those was the "gantlet," a mini-obstacle course involving tire flips, kettlebell swings and a sled pull. "The feedback was everyone loved the gantlet, so we took the running out of it," creator Sean Ofeldt says.

The concept has proved popular, boosting attendance from 500 in the District last year to a sellout field of 1,800 expected from 7 a.m. to 7 p.m. Saturday for the race at the Plateau at National Harbor, Harborview Avenue and Oxon Hill Road. Participation in the event has also increased across the country, which Ofeldt attributes to the fact that it has tapped into a community of exercise enthusiasts who don't normally get to compete. "Runners can go out there any weekend and race," he says. "But CrossFitters, boot campers, where do they stand?"

At Urban Evolution athlete Sean Coyne, 29, of Alexandria, flips an enormous tire 10 times as part of training for the upcoming obstacle course race, Metro Dash. (Katherine Frey/The Washington Post)

One selling point is that the format takes much less time than typical races. Speedsters can tear through the course in six or seven minutes. Even on the slower end of the spectrum, it's over in less than 20 minutes. That doesn't mean it's easy, of course. "You're constantly stressing your body in every plane and switching it every few seconds," Ofeldt says. The course is designed to maximize difficulty, so monkey bars come right after you've pooped out your arms and upper body hauling 35-pound kettlebells around. Just remember that you never have that far to go. "People who try to catch their breath get to the end and think, 'I should have pushed harder,'" Ofeldt says. "Don't pace yourself and you'll walk away happy."