The pistol trains leg strength and also builds the balance and stability you need to make it across obstacles like the balance bridge. To do this one-legged squat, extend one leg out in front of you, keeping it straight. Bend your other knee and, with control, lower to the ground so that your hamstring touches your calf. Press through your heel to stand up. This is an advanced leg move, and you can scale the exercise by lowering your butt onto a bench or stack of weight plates before standing back up (gradually make the bench or weight-plate stack lower and lower). If you've mastered the pistol squat, make it harder by performing it on a Bosu ball. A Ninja champion's challenge? Try it on a medicine ball. Do 10 reps on each leg for a set.