Here's how to do it: Start by kneeling, then place your right hand on the back of your head and your left hand on the floor. Lift your right leg up 2 inches, then crunch to the right while raising your right leg to form a straight line from hip to toe. Lower your right leg back down to 2 inches above the floor. Start with 30 seconds per side and work up to one minute.
Try this move: Triangle Oblique Crunch