A person simply shouldn't sit for any period of 8 hours. That's asking for all sorts of health problems. One should get up regularly and stretch, walk around, get some water, and generally take a deep breath or three. Our bodies need that, they really weren't designed to be sitting for 8 hours, or doing a single activity of any sort for 8 hours. It's really bad for one's health to do something like that over and over. :)