I have been in physical therapy for a pinched nerve in my back and they have advised me to tilt my pelvis back thus straightening my lower back while holding in my stomach. Eventually it becomes more comfortable and 2nd nature. They are right! It even helps my shoulders to stay in the proper position. Also, sitting too low is a big problem. I have my chair (office chair) at it's highest position and a pedestal big enough for both of my feet and foot control to be at a comfortable highth, otherwise my legs would go numb.