CHICAGO, Illinois—A 135-degree sitting position produces the least biomechanical stress on the lumbar spine and might greatly reduce the risk of back pain for the desk-bound, researchers reported at the Radiological Society of North America 2006 Meeting.

"This may be all that is necessary to prevent back pain, rather than trying to cure pain that has occurred over the long term due to bad postures." —Waseem Amir Bashir, MBChB, FRCR.
"We were not created to sit down for long hours, but somehow modern life requires the vast majority of the global population to work in a seated position," lead investigator Waseem Amir Bashir, MBChB, FRCR, clinical fellow in the department of radiology and diagnostic imaging at the University of Alberta Hospital in Canada, said. "This made our search for the optimal sitting position all the more important."

Whole-body positional scanner shows posture effects on spinal disks

The researchers used a whole-body positional magnetic resonance imaging (MRI) scanner to measure lumbar lordosis angles, intervertebral disc heights, and shifting of the disks in 22 normal subjects who had no history of back pain or surgery. They then determined which sitting position caused the least stress on the lumbar spine.

Dr. Bashir emphasized that this study was done with a whole-body positional scanner and would have been impossible on a regular fixed "tunnel" recumbent scanner. The positional scanner allows the subject freedom of motion during imaging.

Each subject assumed three different sitting positions: a slouching position, similar to being hunched forward over a desk or video game console; an upright 90 degree position; and a "relaxed" position in which the subject kept feet on the floor but reclined backward at a 135-degree angle.

Slouching toward chronic back pain

The investigators reported that intervertebral disc height tended to decrease as lumbar lordosis decreased as when the subject moved from reclining to leaning over into forward flexion.

"The optimal sitting position was with a trunk-thigh angle of 135 degrees. This position was shown to cause least 'strain' on the lumbar spine most significantly when compared with an upright 90 degree sitting posture," Dr. Bashir said. Disc movement was most pronounced in the 90-degree posture. The slouching posture produced a reduction in spinal disc height at the two lowest spinal levels.

The researchers suggest that, especially for those who spend long hours sitting, shifting the usual posture from the 90 degree angle usually thought of as normal, to an angle nearer 135 degrees should reduce the lower back stress that contributes to chronic back pain.

"This may be all that is necessary to prevent back pain, rather than trying to cure pain that has occurred over the long term due to bad postures," Dr. Bashir said.

These findings have obvious implications for seating design, and Dr. Bashir suggested that using positional MRI to test future designs might help reduce chronic back problems that result at least in part from bad seating posture.

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Reference

1. Bashir W, Torio T, Smith F, et al. The way you sit will never be the same! Alterations of lumbosacral curvature and intervertebral disc morphology in normal subjects in variable sitting positions using whole-body positional MRI. Presented at: Radiological Society of North America 2006 Meeting; November 27, 2006; Chicago, Illinois. Abstract SSC20-07.