[Etheryte]

Last time I saw my physio, I asked about the exercise ball sitting thing because it had come up in a recent conversation. She smirked, got a ball from the other room and then proceeded to sit down on it with the biggest hunch I've ever seen. You can have bad posture sitting on anything, for most people having the option to support their back is better, because then you're not screwed once your back inevitably does get tired.