hiya steph.....

i have not used an excercise ball---i find them just i little too mushy and unstable which is definitely NOT good for a voluntary dislocator of both hips, both shoulders, fingers, and a knee!!!! lol......but i HAVE used and own a medicine ball which is great for strength training too.....i have a 7-8 pound leather covered one and i specifically use it for outer and inner thighs and triceps i find are easier to do too!!!!

i have also heard that when doing advanced yoga people incorporate the medicine ball.

i purchased mine in the states here at a local sporting goods store for about $37