Ok, I realize that this chair looks crazy. But, let me just tell you about it a bit before you make up your mind about it, ok. My friend's wife had numbness in her arms and legs after she had her baby a few years ago. The doctors could not figure out what happened but apparently there was some nerve damage done sometime during the delivery or pregnancy. Anyway, she sits quite a bit at her desk since she is a CPA and a physical therapy friend of hers told her to try this ball and see if it would help her. So, she got one and has been using it ever since. Basically it is like one of those exercise balls on wheels. I personally was uncomfortable sitting in it, but she has grown use to it and prefers it to any other chair now. And, interestingly enough, as long as she uses this chair at work, she does not have the numbness anylonger. I think the basic reason for the chair is to make sure you sit up with good posture...which I do not so that's probably why it was uncomfortable for me. Anyway, want to improve your posture, of if YOU have some numbness like this lady, give it a shot.