An aching back? Well don't sit up straight!

By using a new form of magnetic resonance imaging (MRI), Scottish and Canadian researchers have been able to show that sitting in an upright position places unnecessary strain on the back.

Sitting in this posture for hours at a time can lead to chronic back pain say the researchers.

Lead author Dr. Waseem Amir Bashir, of the Department of Radiology and Diagnostic Imaging at the University of Alberta Hospital, Canada says "sitting in a sound anatomic position is essential, since the strain put on the spine and its associated ligaments over time can lead to pain, deformity and chronic illness".

The researchers say the best position in which to sit at your desk is leaning slightly back, at about 135 degrees.

Back pain is the most common cause of work-related disability in much of the developed world and is a leading cause of job-related absenteeism.

The study was conducted at Woodend Hospital in Aberdeen, Scotland, and by using a positional MRI machine, the team were able to scan the backs of twenty two volunteers with healthy backs as the patients moved sitting positions during the test.

Traditional scanners have required patients to lie flat, which may mask causes of pain that stem from different movements or postures.

Dr. Bashir says a 135-degree body-thigh sitting posture was seen to be the best biomechanical sitting position, as opposed to a 90-degree posture, which most people consider normal.

Back pain is the most common cause of work-related disability in much of the developed world and is a leading cause of job-related absenteeism.

Dr. Bashir and colleagues hope that by identifying bad seating postures and allowing people to take preventative measures to protect the spine, back strain will be reduced and fewer work days will be lost.

Dr. Bashir says man was not created to sit down for long hours, but somehow modern life requires the vast majority of the global population to do so and the search for the best sitting position was all the more important.

The patients were asked to adopt three different sitting positions: a slouching position, in which the body is hunched forward (e.g., hunched over a desk or slouched over in front of a video game console); an upright 90-degree sitting position; and a "relaxed" position where the patient reclines backward 135 degrees while the feet remain on the floor. Measurements were taken of spinal angles and spinal disk height and movement across the different positions.

Spinal disk movement occurs when weight-bearing strain is placed on the spine, causing the internal disk material to misalign.

The team saw that disk movement was most pronounced with a 90-degree upright sitting posture and was least pronounced with the 135-degree posture.

This they say indicates that less strain is placed on the spinal disks and associated muscles and tendons in a more relaxed sitting position.

The "slouch" position revealed a reduction in spinal disk height, signifying a high rate of wear and tear on the lowest two spinal levels.

Across all measurements, the researchers concluded that the 135-degree position fared the best, and as a result, Dr. Bashir and colleagues advise patients to ward off future back problems by correcting their sitting posture and finding a chair that allows them to sit in an optimal position of 135 degrees.

They suggest 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 posture.

Dr. Bashir says employers could also reduce problems by providing their staff with more appropriate seating, thereby saving on the cost of lost work hours.

The research was presented at the annual meeting of the Radiological Society of North America (RSNA).