A core-strength builder that guards against spine injuries and bolsters balance for knife-edge walking.
Lie on your stomach with forearms planted under you, palms down. Bring your legs together and straighten them, lifting your torso into a plank position so that your toes and forearms are the only points of contact with the ground. Reach your left arm forward and lift your right leg. Hold for one count, return to plank. Alternate sides.
30-90 seconds; 1 set
Beginner: Start on your knees and forearms.
Intermediate: If you can hold here for more than 90 seconds, put on a pack loaded with 15 pounds.
Advanced: Add pack weight until you tire in less than 90 seconds.