By Jennifer Berube
The way you sit will never be the same! So says Dr. Waseem Bashir, a musculoskeletal radiologist in the United Kingdom. A few years ago, Dr. Bashir announced that not only is sitting up straight not the best sitting posture, it is in fact, bad for your back.
Now, this isn’t the first time somebody has come to this conclusion; as Dr. Bashir points out, the normal position of the lumbar spine during sitting has long been debated. 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 isdetermined by maintenance of the trunk-thigh and the knee anglesat approximately 135 degrees.” Note the ‘approximately’, we’ll touch on this later.
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.
But, in November, 2006, Dr. 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.
“When you’re sitting at 90 degrees, that’s not natural because your knees are up and your back’s straight, so you’re actually pushing against gravity,” says Dr. Bashir. “Your abdominals are doing a lot of work trying to keep you straight, that’s why you end up getting tired and you slouch forward.”
On top of workplace fatigue and decreased productivity, Dr. Bashir points out that a well known relationship exists between seating posture and back pain. In an effort to provide data to the general public and start to reduce the incidence of chronic back problems due to bad sitting positions, he says this study has determined the best biomechanically and anatomically ‘neutral’ sitting position using positional MRI.
But while Dr. Bashir wants to bring awareness to the masses in terms of sitting in an open angled posture as opposed to sitting up straight at a 90 degree angle, others aren’t so keen to spread the word.
“In sitting, you have a dynamic spine, the muscles are working to support it,” says Patrice Winter, a practicing physical therapist in Fairfax, Virginia and Fellow of the American Academy of Orthopaedic Manual Physical Therapists. Winter describes a dynamic spine as being in a working relationship with the pelvis, legs and surrounding muscles. She points out that if a person is seated with their spine elongated and toned, the muscles work to support the spine and they work together to have very controlled movements.
“Look at the muscles of the spine, it’s like a tent pole with guy wires coming off of it and if you’re just collapsed in your posture your guy wires aren’t working and so the pole of the tent doesn’t have the support it needs,” says Winter. “Whereas, if you have a nice long spine or center pole of a tent, the guy wires coming off of it are all doing their job, your tent is good and strong.”
The optimal seated posture, according to Winter, would be with the pelvis in a slight anterior tilt, with the hip angle around 120, as opposed to 135. She states that sitting at a 135 angle is going to push somebody out of the chair.
But, Dr. Bashir explains this number is just an estimate, a guideline. He says this reasonably obtuse angle allows the user to sit in a chair, with the seat tilted downward slightly and the feet flat, providing enough of a reclined position to relieve spinal stress, without forcing the user to actually slide out of the chair.
“What we’re saying is the more open an angle you have between your [upper body] and your thighs, the less strain that causes to the overall back.”
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.
“We were made to be mobile, not to be static”
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.
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.
“We were made to be mobile, not to be static,” says Dr. Bashir. “Unfortunately, we’ve come to this kind of culture where most of the day we’re actually more static than we are mobile, we’ll sit in a chair all day long, then sit in a car, go home, sit and watch television and go to bed.”
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’ve shown that even within a 10 minute period sitting in these postures, forward slouched and at 90 degrees, you already start seeing signs of water loss in the discs,” says Dr. Bashir. “Just think of that day in day out, year in year out, you will eventually cause degeneration because you’re in a posture that your body doesn’t like.”
So, to combat low back pain, Dr. Bashir suggests finding a chair that can be adjusted to open up the hip angle. A seat that tilts forward also encourages this natural posture. Further, he recommends positional MRI in the evaluation of future seating design and believes this will help to reduce chronic back problems due to bad seating posture.
Working Ergonomics 
Great findings! I was wondering why I get tired sitting up straight and then my back starts to hurt. It makes alot of sense that the pressure from leaning forward and sitting straight creates back pain. I’m thinking about getting a monster sac instead of conventional furniture for my house.
Hey, great work!
I was wondering what if we just tilt the whole chair at a 30 degree angle and sit in a 90 degree posture