Some guys seek out workouts that push their mortal limits. We get it: There’s a serious rush and point of pride in knowing you completed a physical feat that most people wouldn’t dream of doing. If you’re that guy, and you’ve got the fitness chops to prove it, these workouts—designed by trainers at the top of their fields—may just be the challenge you need to test your limits, and (hopefully) come out victorious. But before you blindly Barney a “Challenge, accepted!” to that headline, take a moment to assess your current fitness level and skill set. There’s a big difference between “not being able to finish” and “getting injured in the attempt.”