Sitting posture

It’s often said that the rear end is the most heavily used part of the human body. If you’re an average person living in the modern world, you spend a lot of time pressing your behind into soft, yielding pieces of furniture. In fact, you probably spend more time sitting down (whether it’s working, eating, driving, watching television, or reading fine books like this one) than you spend in virtually any other position.
With all our experience sitting, it’s a bit disappointing to learn that most of us aren’t very good at it. Proper sitting is surprisingly hard work, especially when you add computers, telephones, and office work into the mix. Part of the problem is that sitting “at the ready” quickly becomes tiring, and good posture requires constant vigilance. One funny Web video later, and you’ll be slouching into your computer screen.
The first piece of advice for long-term sitters is to take frequent breaks. (You can find some simple stretches and exercises you can do without leaving your desk at http://backandneck.about.com/od/exercise/ig/Stretch-at-Your- Desk.) The second piece of advice is to conduct regular “posture checks.” With each posture check, your goal is to review what you’re doing and pull your body back into line. The most common mistakes include pushing out your stomach (which curves and overextends your back), hunching your shoulders, and craning your neck. To make sure you’re sitting pretty, use the picture on this page as a quick posture checklist.
Source of Information : Oreilly - Your Body Missing Manual