Men's Health: Aching back? Don't sit up straight

It turns out your school teachers were wrong when they told you to sit up straight.

Researchers have found evidence that sitting with the thighs and back at a 135-degree angle (slightly leaning back) is in fact the best position for avoiding back pain. To reach this conclusion, they used a special magnetic resonance imaging (MRI) scanner that allowed participants to sit or stand during the test.

"We've always been told to sit up right, but the way you sit will never be the same again," says Dr. Waseem Bashir, a radiology and diagnostic imaging fellow at the University of Alberta Hospital in Edmonton.

His research – which contradicts conventional wisdom about the benefits of a 90-degree posture – has important implications for the vast majority of people who have to work sitting. "The bottom line is that we do not have any chairs that are available to us that are appropriate for the back-seating position.

"The angle of posture has long been questioned and until this study, we'd never been able to accurately assess how we actually sit, how we should be sitting and how our backs look from an MRI point of view."

Fellow study author Dr. Francis Smith, a consultant radiologist at Woodend Hospital in Aberdeen, Scotland, where the back scans were done, says the MRI machine at his institution allows doctors to scan the back while patients sit in different positions rather than lying flat on their back.

In the study, 22 healthy volunteers with no history of back pain or surgery sat in a slouching position, in which the body is hunched forward; an upright, 90-degree sitting position; and a "relaxed" position where the person reclines backward 135 degrees while the feet remain on the floor.

Movement of the discs – the cushioning pads between the backbones – was most pronounced with a 90-degree posture and was least pronounced with the 135-degree posture, indicating that less strain is placed on the discs and associated muscles and tendons in a more relaxed sitting position. The slouch position revealed a reduction in disc height, signifying a higher rate of wear and tear on the lower back.