Step by step instructions
Sit on a Swiss ball, holding both ends of a resistance band anchored behind you. Round spine and walk feet out until mid-back is on the ball and shoulders and head are extended slightly over the top, with feet hip-width apart and under knees. Extend arms overhead by ears with palms facing up. (Move far enough away from the anchor point to keep the band pulled taut. Lower resistance level by moving closer to the anchor point; increase it by moving farther away.)
Slowly crunch up and reach arms across to right thigh, lifting head, neck and shoulders off the ball. Return to starting position. Repeat, alternating sides each rep.