Lie on your left side with your legs straight, hips stacked, left elbow bent and aligned with your torso, head resting lightly in your left hand. Contract your abs to keep your rib cage from sagging, and place your right hand on the ground next to your torso for support. Without rolling forward or backward, lift both legs off the ground, toes pointed. Keeping your hips and shoulders squared, inhale for 2 counts as you move your top leg backward and your bottom leg forward in a "scissors" motion; reverse the motion, moving the top leg forward and the bottom leg backward as you exhale for 2 more counts. Maintain a strong center and an even, flowing pace as you do 10 reps, then bring your legs together, lower them to the ground, roll onto your right side and repeat. Do 10 reps on each side (a rep equals 2 switches).