"do ab-crunches every day"

Crunches don't work so well, they strengthen the wrong muscles for stability. You are far better off holding your lower abs (the ones from belly button to pubic bone) flat all the time. Walking, sitting, standing, biking, ALL THE TIME FOR EVER AND EVER!! Oh, yeah, and if you can't breathe and hold 'em flat at the same time the cruncher-muscles have jumped into the game and taken over from the stabilizers.