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Defying the age-old advice of parents and teachers, a new study shows that you're better off sitting back than sitting up.

An Alberta researcher has found that while seated, with feet flat on the ground, leaning back to create a 135-degree angle between the thighs and trunk is much less straining on the spine and will not lead to the chronic back pain associated with sitting in an upright position for extended periods of time.

"Up until now it's always been, 'Mum knows best,' and so you sit up straight," said Waseem Amir Bashir, a researcher in radiology and diagnostic imaging at the University of Alberta Hospital in Edmonton and lead author of the study.

Back pain is the most common cause of work-related disability in Canada, and a major cause of lost work time, according to Statistics Canada. The agency estimates that between 70 and 85 per cent of Canadians will have some kind of back problem during their life.

"We live a sedentary lifestyle," said Dr. Bashir, who presented the findings yesterday at the Radiological Society of North America's annual meeting in Chicago.

"We weren't made for sitting for such long periods of time."

Using a new type of a magnetic resonance imaging scanner that allows patients to move freely within it, Dr. Bashir and his colleagues were able to monitor spinal disc movement in 22 healthy subjects for various postures. Traditional MRI machines require patients to lie flat and can mask causes of pain that come from different movements or positions.

They found that sitting at a 90-degree angle puts significant strain on the spinal discs and back muscles because of the force of gravity.

Slouching or hunching forward is even worse, because it compresses the spinal cord and "essentially just pops your discs backwards."

But having the upper body at 135 degrees to the thighs in a "relaxed" position alleviates nearly all pressure on the lower spinal discs and causes the least damage over extended periods of time.

The researchers came up with this angle because it allows the discs to be perfectly aligned and resembles lying flat on one's back, which is the ideal position to avoid pain.

By highlighting the benefits of sitting back, Dr. Bashir said he hopes people will begin to take preventive measures to reduce back strain and subsequent missed work days.