CHICAGO — Straight backed isn't the optimal sitting position for the spine, according to a study conducted in Scotland using positional magnetic resonance imaging.
The study demonstrated that a 135-degree body-thigh sitting posture, in which the hips are higher than the knees, causes less strain on the lumbar spine and most simulates the “relaxed” supine position, Dr. Waseem Amir Bashir said at a press briefing during the annual meeting of the Radiological Society of North America.
“I know we've always been told to sit up right with our backs straight, but our study shows that this position is not naturally favorable for your back at all,” he said. “The bottom line is that we don't have any chairs available to us that are appropriate for the best sitting position.”
The study included 22 healthy volunteers (mean age, 34 years; weight 67 kg; height 169 cm) with no history of back pain or surgery who underwent measurements of lumbar lordosis angles, intervertebral disc (IVD) heights, and translation of the nucleus pulposus using a 0.6 -tesla whole-body, positional MRI scanner.
The patients were scanned in three different positions: a slouching position in which the body was hunched forward, as if over a desk or video console; an upright 90-degree sitting position; and a relaxed position where the volunteer reclined backward 135 degrees while the feet remained on the floor.
Each scan was separated by a 10-minute supine rest period because at least 10 minutes is needed by the body to rehydrate intervertebral discs, Dr. Bashir said. Research has shown that as much as 75% of disc height, lost throughout the day, can be regained with a 20-minute supine rest.
The worst position for the spine—as reflected in disc height—was the slouching position, followed closely by the upright 90-degree position, the University of Aberdeen (Scotland) investigators reported.
Disc heights decreased as lumbar lordosis increased in each sitting position from reclining to forward flexion. The two lowest spinal disc levels, the L4/5 and L5/S1, showed the greatest loss of disc height. “Even if it's only 2 mm at the second lowest levels, if you add it all up, it's quite significant,” said Dr. Bashir, now a clinical fellow at the University of Alberta Hospital, Edmonton.
There was a significant difference for the upright and slouched positions, compared with the 135-degree and supine positions in disc height and movement of the nucleus pulposus, the gel-like mass that forms the middle of an intervertebral disc.
Disc movement was most pronounced with the forward slouching position, while the 90-degree position showed a slight movement backwards, he said. The 135-degree position was similar to a supine position, placing very little strain on the spinal discs and associated musculature, he said.
The 135-degree position has found its way into seat designs for luxury auto manufacturers. But until furniture makers take note, Dr. Bashir advocates the use of adjustable desks and chairs, and footrests.
The two worst positions: MR images show that disc height was most diminished amongthose slouching forward (left) and those sitting perfectly upright at 90 degrees. Photos courtesy Dr. Waseem Amir Bashir/RSNA
