Distance: 3.2–5 miles (Sprint), 8 miles (Super), 12 miles (Beast)

Obstacles: 15 (Sprint), 20 (Super), 25 (Beast)

Difficulty: "We designed our sprint to be as hard as the regular Tough Mudder," says Joseph Desena, founder of Spartan Race. Unlike TM, Spartan is a competitive, timed race with lots of fast climbing, heavy objects, and consequences – such as getting clobbered (see left).

The Vibe: There's camaraderie at the finish, but don't come for the party. Desena hopes Spartan will one day be an Olympic event (it's a varsity sport in 66 high schools), and the competitors take it seriously.

Cost: $60–$205; spartanrace.com