I'm curious too. The ab excercises that I do at Curves and at home (slow-motion crunches mainly) really seem to work the upper and lateral abdominal areas and not really the lower (aprony) ab area.

Though I have felt the "burn" in that area when doing slow-motion leg lifts (lie on the floor with a pillow under your head, lower back kept pressed into the ground - that's the most important part, it's the real excercise! - then s-l-o-w-l-y lift your straight legs off the floor up to 6 inches and then just as slowly lower, if you can do more than 8 you are moving too fast.)

But while that feels like it's tightening the muscle underneath it isn't shaping or tightening the apron itself.