Not only does this move work all four abdominal muscles, but the glutes are targeted as well, giving a nice lift to your powerful rear.
Put your hands on the ground and the top of your feet on the ball so your body is in an L shape to the ground (head facing down). Keep your core tight to keep balance.
Pull your navel into your spine and lift your bottom into the air using your core.
Maintaining balance, lower your bottom back to the first L position.