Go ahead, sit back, relax

Forget all that nagging about sitting up straight. The healthiest position for the back, it turns out, might be a comfortable 135-degree angle.

“Everybody says, ‘Mind your posture,’ but sitting at 90 degrees is not good,” nor is slouching forward, says Waseem Bashir, clinical research fellow in musculoskeletal radiology at the University of Alberta in Canada.

He and other researchers examined 22 healthy people with no history of back pain or surgery. Using a new MRI machine that allows people to be scanned while seated, they took MRIs of each person as they were lying down, in a 90-degree seated position, in a forward-slouched seated position and at a 135-degree seated position.

The tests revealed that sitting upright or slouched over for 10 minutes strained the erector spinae muscles, which run along each side of the spinal column. It also compressed the intervertebral discs in the lower back, resulting in a 20 percent water loss from the nucleus pulposus, the soft, jelly-like central part of the disc, which acts as a ball bearing. At the 135-degree angle, there was almost no water loss, muscle strain or compression.

At the upright and slouched positions, the spine also lost its natural curvature, which was present at the 135-degree angle.

The research was presented recently at the annual meeting of the Radiological Society of North America in Chicago.