[throwaway-1209]

The best ab exercise that I have found is a heavy ass deadlift. Barbell squats are good too. They actually train _core strength_ rather than just abs, which is what you need. The advice is: start with compound barbell exercises like squat and deadlifts, then incorporate others as needed. Don't ignore cardio.

[Evolved]

Agreed but substitute swimming or elliptical for jogging/running as the lower impact will be easier on the back and accomplish the same thing.

[toasterlovin]

Deadlifts and squats, properly performed (and in many instances, performed improperly) are not hard on the back. If you start with an empty bar and add a little weight each time, they will make every part of your back stronger and more resilient to the vagaries of life as a physical being.