I agree with Kathryn, get an anti-burst ball if your going to do full body-weight or use any type of dumb bell, weighted ball, anything that adds weight. I've had the normal ones burst before, (before the anti-burst) came out. The normal one will shoot out from under you, if it pops, you'll be on the floor, with the wind knocked out of you, brused, and maybe broken in places. This was actually how I broke my tail bone a few years ago. I was doing crunches on a firm ball, and someone had it before me who had something sharp in a pocket. I didn't know, After 2 crunches I here SHHHH and next think I know, is I'm flat on my back, with the wind knocked out of me, and my butt is on fire. As since with a crunch your at an angle, your bottom hits first then your back and when you here SHHH there is no saving yourself. As it seems shoots away about the same time you here it.
But having a sore behind is one of the worst things, you can bend down, you can't sit, you can't stand, and you can't lay down without it hurting. But on a good note got a cheap re-arrangement of my tailbone which was actually something that I was thinking about having done. As my tail bone staight out instead of went down like a normal one, and just rolling back on the step/bench, like Cathe does in PS or S&H, was nearly impossible for me then as my tailbone was out instead of tucked under. Now I can do it, without the pain.
Kit
