lower ab situp.
i just foud out about this the other day, if you already know about it good for you
1) lie down
2)put left foot on the groud so that the leg is bent
3) cross right leg over (like a triangle except the foot is ontop of your thigh)
4) using just your hips bring your crossed leg/knee as close to your chest as possible
you will feel the burn a little bit into it.
i do 75 each side right now with 15 sec rest inbetween sides.