A version of the classic, using a fit-ball.

Sit on the fit-ball, your bottom slightly on the front of it, with your legs facing forwards, feet apart for balance, and your hands behind your head. Put yourself in the Neutral Spine Position.

Lean backwards lowering your upper body onto the fit-ball, and then use your stomach muscles to raise it back to the sitting position. Keep your eyes looking at the ceiling as you come up.

You must use your core muscles to control the fit-ball and keep it in the right position.