Yesterday at the gym I used resistance bands to work my abs. I held the handle of the bands behind my neck with my elbows up by me ears. On my knees I crunched into a for lack of a better word ball. By using the resistance band I worked my abs hard. They hurt today, and it has been a while since any core exercises made me hurt. Abs of steel baby!
Here are some pictures of me doing the exercise. My kids were in charge of the picture taking so they may not be the best but it will give you the gist of the move.