Sit up straight? No mom, you're wrong

New York: ''Sit up straight -- you'll hurt your back,'' Mom always said. It turns out Mom was wrong, according to a new study that found sitting in an upright 90-degree position places more strain on the back than sitting in a slightly reclined 135-degree position.

The findings were reported this week at the annual meeting of the Radiological Society of North America in Chicago.

''Everybody knows that if you sit for long periods you have back pain,'' a radiologist from the University of Alberta Hospital in Canada, Dr Waseem Amir Bashir said.

To search for the optimal back-friendly sitting position, Bashir and colleagues used a ''positional'' MRI scanner to study 22 healthy adults with no history of back pain or back surgery as they sat in three different positions: a slouching position in which the body is

hunched forward, like over a keyboard; an upright straight-back position with legs at 90-degrees and knees and hips at the same level; and a ''relaxed'' 135-degree tilt back position.

''In this position, the legs are lower than the hips and the back is slightly forward with a normal curvature which provides lumbar support,'' Bashir explained.

''We found that the reclined 135-degree position is the ideal sitting position because it actually is similar to a neutral relaxed lying down position,'' Bashir added.

Potentially harmful spinal disk movement was most pronounced with the 90-degree sitting position; it was least pronounced with the 135-degree relaxed position, indicating that less strain is placed on the spine and associated muscles and tendons in this position.

''With the 90-degree sitting position, your back goes completely straight and you're actually straining your back against gravity,'' Bashir noted.

As expected, ''the bending forward or slouching position is the worst sitting position for your back,'' he said.

So for desk-bound workers who want to protect their backs or relieve their aching back, Bashir and colleagues advise finding a chair that allows one to sit at a 135-degree angle.

"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.

Providing this type of chair is likely to be cost-effective for employers, given that back pain is the most common cause of work-related disability in the US and a leading contributor to job-related absenteeism.