Q4: How do I exercise the abs?

The abs are designed to perform one main task, to shorten the distance between your sternum, or breastbone, and your pelvis. The only way to do this is to bend your spine in the lower back region.

In short, any exercise which makes you move your sternum toward your pelvis or your pelvis toward your sternum is good. To do this safely, the lower back should be slightly rounded, not arched.

In general when exercising the abs, try to maintain the natural arch of you lower back. The lower back will round slightly as you perform the exercises. Don't fret about pressing your back into the ground.