November 27, 2006
Conventional Wisdom On Good Posture All Wrong

Ever since I was a child I've read in low lighting conditions and continue to do so to this day. Yet as a kid I was repeatedly scolded and told that reading without lots of bright light would damage my eyes. I didn't believe these claims (having discovered that lots of things adults believe are not based on any scientific knowledge). Several years ago I came across an article which quoted a chairman of a medical school ophthalmology department who said that reading with little light will do no harm to your eyes and that claims to the contrary are just a popular myth.

I also sit with a chair tilted back and have also done that for as long as I can remember. I've been waiting for evidence that vindicated me on that choice too. Now researchers in Scotland think they've found evidence that the conventional wisdom on correct sitting posture is bad for your back and you are best off with a higher angle between your thighs and torso.

CHICAGO -- Researchers are using a new form of magnetic resonance imaging (MRI) to show that sitting in an upright position places unnecessary strain on your back, leading to potentially chronic pain problems if you spend long hours sitting. The study, conducted at Woodend Hospital in Aberdeen, Scotland, was presented today at the annual meeting of the Radiological Society of North America (RSNA).

Normal is bad.

“A 135-degree body-thigh sitting posture was demonstrated to be the best biomechanical sitting position, as opposed to a 90-degree posture, which most people consider normal,” said Waseem Amir Bashir, M.B.Ch.B., F.R.C.R., author and clinical fellow in the Department of Radiology and Diagnostic Imaging at the University of Alberta Hospital, Canada. “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.”

Back pain is the most common cause of work-related disability in the United States, and a leading contributor to job-related absenteeism, according to the National Institute of Neurological Disorders and Stroke. By identifying bad seating postures and allowing people to take preventative measures to protect the spine, Dr. Bashir and colleagues hope to reduce back strain and subsequent missed work days.

“We were not created to sit down for long hours, but somehow modern life requires the vast majority of the global population to work in a seated position,” Dr. Bashir said. “This made our search for the optimal sitting position all the more important.” The researchers studied 22 healthy volunteers with no history of back pain or surgery. A “positional” MRI machine was used, which allows patients freedom of motion—such as sitting or standing—during imaging. Traditional scanners have required patients to lie flat, which may mask causes of pain that stem from different movements or postures.

The patients assumed 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.

That bolt upright sitting posture shows the most sign of strain on the spine.

Spinal disk movement occurs when weight-bearing strain is placed on the spine, causing the internal disk material to misalign. Disk movement was most pronounced with a 90-degree upright sitting posture. It was least pronounced with the 135-degree posture, indicating 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. As a result, Dr. Bashir and colleagues advise patients to stave 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.

“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,” he added. “Employers could also reduce problems by providing their staff with more appropriate seating, thereby saving on the cost of lost work hours.”

What I still want to know: Should one lean back and have just the upper part of the back touch the back of the chair? Or should the whole chair back be tilted at the same angle as the back and touch the back all the way down?

Share |      Randall Parker, 2006 November 27 10:49 PM  Health Unconventional Wisdom


Comments
Frank said at November 28, 2006 6:18 AM:

The problem with "bolt upright" is the "bolt" rather than the "upright". The spine is not a straight length of bone, but a
gracefully curved one, and those curves are designed for flexibility and support. Often when people think they're sitting "up straight", they're actually straining their back muscles and spine into an unnatural position, which, combined with neck strain from failing to balance their heads comfortably, over time causes problems. Sitting at an angle greater than 90 degrees will likely cause someone to collapse their head and neck downward, which can lead to neck and upper back pain. It may feel good compared to sitting stiffly upright, but over time, unless you identify and eliminate strain, you'll likely run into problems.

Julie said at November 28, 2006 11:04 AM:

I can read a book in that 135 degree position -- but I sure can't see what's on the screen! How am I going to get any work done?

Forbes said at November 28, 2006 11:40 AM:

Julie: A laptop (computer) gets its name for a reason. I sit in a recliner working from my laptop. I also have a ruptured (L5) and herniated (L3) disc. As to the host's question regarding leaning back--it's best to have full support (for your weight) along the length of you back, not just across the top of your back, as if you were balancing against the top of a seat back.

Robert Schwartz said at November 28, 2006 9:02 PM:

Last year, when I had sever back pain, I found that sitting up very straight gave me the most relief. I discovered that putting the keyboard of my computer on top of my desk, rather than in the keyboard tray forced me to sit up straighter and made me feel better. YMMV.

Anonymouse said at November 29, 2006 9:26 AM:

I think the problem might be all this proscriptivism regarding seating positions(and tons of other stuff like this). We all want to find the "best" position, and then put all our effort into trying to reach it. Employers will think it's a good idea to buy chairs that FORCE everyone to sit in the position that they think is the best.

When you're sitting at your desk at home, the place you get to decide how you're going to sit, do you just pick one position and stick to it forever? Or do you shift around in your seat, from time to time; ten minutes slouching, thirty reclining?

I think the best solution is to find chairs that let people move around, and sit how they want to when they feel like it. Ones that allow some flexibility so that you can shift tension from a certain area when it builds up too much. But I guess that's just too much to ask in the modern work-a-day world.

James said at November 29, 2006 1:16 PM:

The 135-degree angle is about the same as the angle produced by those "kneeling" chairs popular a few years ago. Of course those can hurt your knees. But the concept is right; rather than reclining your back (and possibly requiring you to hold your head and neck at an odd angle if what you're doing while in the chair still requires you to look straight ahead), you lower your knees. You can achieve a similar effect just by sitting at the edge of your chair, with your thighs canted down a bit, and your feet underneath the chair. The critical interface is between your spine and pelvis. If your thighs are parallel with the floor, your pelvis is tipped back slightly, and the bottom of your spine is tipped back as well, and then the rest of your spine has to compensate by bending forward to achieve a "bolt upright" position. If your thighs are tipped down a bit, your pevis can tip forward slightly, allowing your spine to start out going straight up.

It also helps to remember that your spine is in roughly the center of your body, and not at the back. Those pointy things running up your back are just the *tips* of your vertebrae. This is important because how you perceive your body as working affects how you use it; if you think of your spine as being on your back, with your chest and shoulders hanging forward off of it, you will tend to slouch, and when you try to sit upright, you will visualize your body hanging off of a stiff spine at the rear of your body. This then causes you to use unnecessary muscles, adding to your back strain.

Bill said at December 27, 2006 7:51 AM:

Hello Everyone.

I saw this thread and wanted to tell you about the lapdesk I've had for a year or so. It has a pillow on the bottom that can be tilted to make my laptop computer comfortable for me. I think there are a couple of other products out there made for the same reason- but this one has been good.

Here is where I got it.

http://search.ebay.com/_W0QQsassZeasy_buysQQhtZ-1

Bill

Joe said at March 31, 2009 10:13 AM:


Some student from Ireland seems to have a good idea going. Not sure if there's any testing done, but there's a flexible seat and height adjustment which I really like for kids.
www.perch.ie

Probably wont see the light of day though! Pity

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