Lie with your back flat on an exercise mat and your feet resting on top of a Swiss ball. Keeping your core braced, lift your hips and use your feet to roll the ball away from you until your legs are fully extended. This is the start position. Keep your shoulders flat on the ground and the rest of your body in one unbroken line. Proceed to bend your knees and pull your heels towards you so that the ball is pulled towards you also. Keep your hips elevated throughout. Hold for a count of one. Return to the start position by extending your legs until they are straight. Repeat.