"Sit UP straight, young man!!"--turns our this was really bad advice from your teachers...

From BBC: Sitting straight 'bad for backs'

""Sitting up straight is not the best position for office workers, a study has suggested.
Scottish and Canadian researchers used a new form of magnetic resonance imaging (MRI) to show it places an unnecessary strain on your back. They told the Radiological Society of North America that the best position in which to sit at your desk is leaning back, at about 135 degrees. Experts said sitting was known to contribute to lower back pain. Data from the British Chiropractic Association says 32% of the population spends more than 10 hours a day seated....""