Aside from his slew of insane adventures on Discovery Channel's series Man vs. Wild, Bear Grylls races Tough Mudders. And the 12-mile race isn’t dubbed the world’s toughest for no reason—it’s loaded with 25 military-style obstacles (including a vegetable oiled half pipe and an electric shock field) intended to trip you up.

Getting through it takes a ton of physical, but most importantly, mental strength, says Grylls. So how do you train for (and survive) such a beast of a race? In an exclusive interview with Men’s Fitness, Grlls gives us a run-down on Tough Mudder training, complete with mistakes to avoid, race-day nutrition tips—and the one thing that can make or break your finish.