Spartan Race (Killington, VT)
Credit: Brent Doscher / Nuvision Action Image

Like Tough Mudder, Spartan Race can also be credited with the explosion of so-called "mud runs," "fun runs," and obstacle course races that began in 2010. It's no coincidence that fitness regimens like CrossFit, P90X, TRX, old-school calisthenics, and other cross-training programs have also made their way into mainstream fitness circles around the same time: They prepare athletes to climb walls, hop between tires, carry heavy objects, and throw spears – all obstacles in the Spartan Race.

Call it functional fitness, the next evolution in the way we work out – whatever you want – is a big enough deal that runners should take note. Though not typically as difficult as Tough Mudder, Spartan Race is a timed event, so competitive types are attracted to the possibility of winning or seeing their faces on the Wall of Champions. This race also offers courses of different lengths and difficulties throughout the year, ranging from the Sprint (3+ miles, 15+ obstacles) to the Beast (13+ miles, 25+ obstacles).

If that sounds like a breeze, try the application-only Ultra Beast, a marathon-length Spartan Race with more than 50 obstacles at Killington Resort in Vermont.

More Information: All of the Spartan Race events are open registration, except the Ultra Beast, which requires an application. [Late September;]