I have four different combos that I do. 1 and 2 I like. 3 and 4 are horrible. I can't decide which is worse - lying around on the floor with a gigantic exercise ball between my legs or lying around on the floor with my legs splayed up in the air. Those days really do a number on my back, but I find if I'm carefull to press the small of my back against the floor, it's tolerable.

But then my neck hurts. ;)