>My girlfriend has a similar chair. I don't like it. I don't have to be on it long before my back starts to hurt.

Our HW supplier brought a couple of those with other hardware for our stand at a computer show in 1989. I tried to sit on one of those. My back outlasted my knees, I couldn't do more than 20 minutes on it.

Maybe that's the idea, you suffer first and later you don't even need the gym, all the workout you need is just sitting :)