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By ANAHAD O’CONNOR
Published: December 12, 2006
THE FACTS Sit up straight, parents tell their children. It’s a well-known refrain, repeated through generations and based on the theory that anything other than a 90-degree posture places undue strain on the back.
Despite its persistence, that advice is wrong. Parents may insist that sitting up straight with your thighs parallel to the ground is the best way to sit, but a long list of studies has shown that that position increases stress on the lumbar disks in your lower back.
Thirty years ago, scientists first showed this by inserting needles into the backs of volunteers and measuring the amount of pressure created by various seating positions. They found that a reclining position was ideal, placing the least strain on the back and minimizing pressure that could lead to back problems. Since then, multiple studies have confirmed that finding.
But it was only in 2006 that scientists produced direct visual evidence. In a study that used new magnetic resonance imaging machines that allow people to sit instead of lie down, a team of researchers at the University of Aberdeen in Scotland looked at 22 volunteers who sat in three positions. The first two positions, sitting upright and sitting with the body hunched forward, produced the greatest spinal disk movement, causing the internal disk material to misalign. The third position, in which the subjects reclined at a 135-degree angle with their feet planted on the floor, created the least strain.
According to the study, any position in which a person leans back, opening the angle between the thighs and the back, is preferable to sitting up straight.
THE BOTTOM LINE Sitting upright at a 90-degree angle strains your back; leaning back places less pressure on the spine.
http://www.nytimes.com/2006/12/12/he...tml?ref=health