Too many S words? Sorry! Oops. Did it again. Anyway, here is a fit ball workout from Women's Health Magazine online. A brilliant source of workouts that are searchable and printable. Please, set up near a mirror if you don't have a friend who can check out your form during these exercises. If your belly is sagging, you are going to STRAIN your spine. Now that is two S words together that you never want to combine.
* These exercises CAN be done with a foam roller or medicine ball. Talk to a trainer!

Draw your belly muscles inwards and upwards towards your navel - think abs of steel
Hold
Breathe in through the nose
As you exhale with control through the lips, draw your belly in a little tighter
Only hold as long as your technique is spot-on. Don't pretend.