We’ve always been told to sit up straight, but evidently we’re better off sitting back.

A study confirms what many ergonomic experts and yoga advocates have been saying for some time — humans aren’t made to stay bent at 90 degrees for any length of time.

Instead, "a 135-degree body-thigh sitting position was demonstrated to be the best biomechanical sitting position," said Dr. Waseem Bashir, a clinical fellow in radiology and diagnostic imaging at the University of Alberta Hospital in Canada.

He presented his findings Monday at the annual meeting of the Radiological Society of North America, in Chicago.

"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. This made our search for the optimal sitting position all the more important."

Back pain affects roughly half of all adults around the globe at one time or another. It’s a $4 billion-a-year problem in the United States, second only to the common cold in lost workdays.

Bashir’s study, conducted at Woodland Hospital in Aberdeen, Scotland, involved 22 health volunteers with no history of back pain or surgery. A "positional" magnetic resonance imaging (MRI) machine was used, which allows patients full freedom of motion — sitting or standing — during imaging sessions.

The volunteers were examined while they were in three different sitting positions: a slouching position, such as one might assume while working at a desk or in front of a videogame console; an upright 90-degree sitting position; or a "relaxed" position, in which one reclines backward 135 degrees with the feet remaining on the floor.

Measurements were taken of spinal angles and spinal-disk height and movement in each of the positions.

Spinal-disk movement occurs when weight-bearing strain is placed on the spine, causing internal disk-cushioning material to be compressed and misaligned. Disk movement was most pronounced in the 90-degree upright position. Disks were least disturbed at the 135-degree position, indicating that less strain is placed on spinal disks and associated muscles and tendons in a more relaxed sitting position.

The slouching position showed a reduction in spinal-disk height and indicated a high rate of wear and tear on the lowest reaches of the spine.

So, Bashir urges a search for chairs that allow workers to sit back while still reaching keyboards and control panels. "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," Bashir said.

On the Net: http://www.rsna.org

(Contact Lee Bowman at bowmanl(at)shns.com.)