The ball burst after using for only a few months. I'm 5 2' and 115 lbs and used it for occasional lower back support during core work. There is no reason it should have burst, aside from being poorly made.
There isn't a way to fill it up properly. The straw thing that they give you doesn't work well. I was expecting a place you can put in a needle and pump it up. It doesn't stay inflated either. Pretty much a waste of money.