When I’m out in the world wearing my “Ergonomist” hat, I seem to run into two types of people: Those who sit upright at the computer, and those who think they should. The virtuous ones tell me that they sit upright when working at their computer, and the others apologize for not doing so.
It seems that nearly everyone believes that “good posture” at the computer means sitting straight upright with a 90 degree thigh/ hip/ trunk angles.
If you read the scientific evidence, however, it turns out that the upright 90 degree posture is not “the best posture”, and it can actually place significant strain on the lumbar spine.
So where does this misinformation come from?
Some people tell me (choose one…) “my teacher, parents, piano instructor or health care provider said sit up straight, don’t slouch”. Others refer to web or print materials from practitioners and manufacturers -- you have probably seen various iterations of the line drawings showing human figures sitting rigidly straight up as they work on a computer (including the one from OSHA shown in this article).
Interesting story here: My friend Tom Albin served on the committee that drafted the ANSI/HFES 100-1988 Ergonomics Standard and he said at the end of the committee’s work one member suggested putting an image on the cover. For no particular reason the upright seated reference posture was selected. Tom said “If you read no further than the cover you might assume this was the one recommended posture”, but the standard actually recommended changing positions and gave four recommended postures including: Reclined, Upright, Thighs Declined, and Standing.
In the www.Office-Ergo.com web site, the late Dennis Ankrum, attributed the perpetuation of this misinformation to these influences:
- We’ve heard it all our lives.
- Everybody we know seems to think the same thing,
- It sort of makes mechanical sense (but not biological sense!),
- We actually heard or saw it RECENTLY, perhaps in a sales presentation for some kind of ergo gizmo.
What is the ergonomics science saying about the upright posture?
Sitting in an upright posture with the thigh/ hip/ trunk angles near 90 degrees causes the pelvis to rotate backwards and flattens the normal lumbar curve. Changing the curvature of the spine like this significantly increases the lumbar disc pressure.
- The upright seated posture increases spinal pressure by 40% as compared to standing upright, and
- The upright seated posture is twice as hard on back as compared to reclined sitting.
So how big is the back pain problem?
Low back pain continues to be among the most common complaints for adults, and is one of the most common reasons given for doctor visits:
- According to a University of Missouri- Columbia School of Health Professions report, there is an 80% lifetime prevalence of low back pain for adults. At any given time, 20-30% of us will have back pain, and back pain is usually recurrent and often progressive.
- A spinehealth.com poll showed that 70% of all respondents report increased low back pain after sitting at work (15% report no change and 15% report improved back pain).
What are the recommendations for seated computer work?
- Regularly move and change positions
- Reduce lumbar strain with an open hip angle greater than 90 degrees.
- Reclining against the back rest opens the hip angle and restores the normal curve in the spine while also shifting much of the upper body weight onto the backrest and further reducing spinal loading. (Reclining beyond a 120-130 degree back angle can result in significant neck flexion when viewing the monitor, however.)
- Sitting upright with declined thighs (tilt seat down in front) also results in a more normal lumbar curve and significant reductions in spinal disc pressure.
How do we enable this healthy seated posture?
- Teach appropriate behavior and the risks of inappropriate positioning.
- Engineer the work system (chair, monitor, input devices etc.) to support a variety of healthy postures. Teach the user how to make adjustments including:
- Adjust the seat pan depth to allow the user to reach the back rest
- Adjust seat pan height and tilt if using thighs-declined position
- Adjust the back rest to recline (unlock the mechanism if required)
- Adjust the recline tension to provide support and allow movement
- Adjust the monitor viewing angle (tilt the screen up or down to new eye-height)
- Adjust the monitor to eye distance or image size for a new viewing distance
- Adjust the arm rests and input devices for easy reach and operation
About the author: Gene Kay has a Masters degree in Exercise Science and is a Certified Professional Ergonomist. He is the President of ErgoAdvocate LLC., a joint-venture with Ergoweb Inc. He has held leadership positions with several organizations including serving as the Past-President of the Upper Midwest Chapter of Human Factors & Ergonomics Society, the Global Ergonomics Manager at American Express, and as the Rehab Services Manager for a multi-center Neurology clinic. Gene is a regular speaker on ergonomics & workplace health at many regional and national educational conferences, and a regular contributor in the Ergoweb Community.
Originally published on ergoweb.com July 8, 2014.