Place your elbow on the ball and lie across the ball in a split stance. Lean into the ball, push up with your elbow and keep a straight line down the centre of your body. Brace your abs and hold. Do it on both sides.
Lie on the ball with your shoulders and head supported. Move your arms into an outstretched position and, resisting the urge to rotate, sway out as far as you can to the side without losing your balance.