i just started to isometric work on the ab ball or swiss ball or whatever you guys call them. I used to think it was for soft cocks and chicks but fuck i was wrong. Try balancing on your knees on a ball. When you can do this with a straight back, Try holding a medicine ball out in front, then to the side, then the other side. Your abs are just a mess trying to stabilize you. You know you've worked them the next day!