Upgrade to Spartan
Credit: Justin Tallis / AFP / Getty Images

Super Spartan

Distance: 8-plus miles, usually off-road
Intensity: High. "It's only 8 miles, but with the obstacles, it actually takes me longer to finish than a half marathon," says pro racer Hobie Call.
Training: 3 to 5 times a week
Obstacles: 20-plus, including carrying 70-pound sandbags and traversing a rope over water. Skip one, and you have to do 30 burpees. [spartanrace.com]

Tough Mudder

Distance: 10 to 12 miles
Intensity Level: It depends on the race. Some are mild, but do one that's hilly or more than 10 miles long, and you will be tested. "Most courses are just as tough as Spartan courses, but the mentality is different," says Call.
Training: 3 to 5 times a week
Obstacles: 20 to 25, including plunging into ice water and running through a muddy field strung with live electrical wires. [toughmudder.com]