Mountain climbers, like burpees, can be done anywhere, and are one of the best all-around exercises that will work you top to bottom with simple movements. Centered around the stomach-hardening posture of the plank, a mountain climber will work your legs, arms, and core, not to mention force you to concentrate on your coordination and agility. When the race course turns vertical, you’ll also appreciate the power you’ve generated with your time spent mountain climbing. While you’re down on the ground, you can also do a few 25′ bear crawls to better ready yourself for barbed wire obstacles.
To do a mountain climber, simply assume the push-up plank position, and bring your right knee towards your chest, planting your right foot in the ground approximately halfway between where your foot was and your hands are. In one motion kick your left leg up as if to assume a position symmetrical with your right leg, while simultaneously kicking your right leg back to take a position that would have been symmetrical with where your left leg just was. Repeat, alternating the right and left legs, counting each pair of leg movements as one rep.