Good chair!!!!
Fishy,
Greg nailed it.
Sitting should NOT be painful. If you are experiencing back pain, even if you have had a back injury in the past, the proper chair along with the correct table height should relieve it.
It doesn't have to be a particularly expensive chair, but you do need it adjustable for height, and for lumbar support. Any decent wheeled office chair should suffice, and if cost is an object, you can get good used ones at many office furniture stores.
Most folks set their chair seats too high causing you to hunch over while working.
You want to sit comfortably, back straight, arms at elbow height or slightly raised. Don't 'lean in' to get closer to the fly, move the chair closer to the desk.
If you can't figure out what height/type of chair will work comfortably for you, consult your back doctor or a physical therapist. Those folks can figure it out for you.
Good luck!
Buddy
It Just Doesn't Matter....