Relieving Spinal Stress

In 1953, American orthopaedic surgeon, J.J. Keegan documented spinal positioning with a series of x-rays. With his patients lying on their sides, Keegan recorded the lumbar spine in standing, right angle sitting, and bent over positions. He concluded, “The normal curve of the lumbar spine in adult man is determined by maintenance of the trunk-thigh and the knee angles at approximately 135 degrees.”

There are two major flaws with Keegan’s research, however. First, he only studied 4 individuals and second, a normal sitting position does not involve lying on one’s side.

Don’t Sit up Straight!

In November, 2006, Dr. Waseem Bashir and a team of researchers confirmed Keegan’s findings. Bashir led a study, conducted at Woodend Hospital in Aberdeen, Scotland, to define the optimal sitting posture by investigating changes in the lower back contours and spinal disc shape using whole-body positional MRI.

The new magnetic resonance imaging (MRI) scanner allowed each of the 22 subjects to sit up, simulating three seated postures, while evaluating the lumbar spine and surrounding muscles, nerves, tissues and ligaments for any signs of degeneration or injury.

The study concluded the best seated posture is the open angle (135 degree) trunk-thigh posture. Of the three seated positions, this appears to cause the least strain on the lumbar spine. The worst seated posture is the forward bending position, like hunching over a desk. This is followed closely by the 90 degree posture with a straight back and legs parallel to the floor.

Alterations of Lumbosacral Curvature and Intervertebral Disc Morphology

On top of workplace fatigue and decreased productivity, a well known relationship exists between seating posture and back pain. In a healthy spine, there are three natural curves: the cervical, which curves inwards at the neck; the thoracic, the curve outwards in the middle; and the lumbar, the inward curve in the low back. When the lower back curves in too far lumbar lordosis occurs. This condition puts pressure on the entire back and can lead to pain and restricted movement.

Bashir’s research found the intervertebral disc height showed a tendency to decrease the more the subject bent forward, with the two lowest spinal disc levels showing the greatest loss of disc height. The nucleus pulposus, or inner gel of the spinal disc, was seen to move the most at all spinal disc levels when bent forward. The least amount of spinal disc movement occurred when the subject sat in the 135 degree posture, which means less strain is placed on the discs and lower back when sitting in this open position.

According to the National Institute of Neurological Disorders and Stroke, nearly everyone has low back pain sometime in their lives and men and women are equally affected. It occurs most often between the ages of 30 and 50, due in part to the aging process but also as a result of sedentary life styles with too little exercise.

We live in a culture where it's common to have back pain and sitting can aggravate a low back condition. Lifting, bending, twisting, it all adds up and experts stress maintaining ergonomic habits at home, as well as at work. So, to combat low back pain, many experts suggest finding a chair that can be adjusted to open up the hip angle. A seat that tilts forward also encourages this natural posture.