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Office Chairs: Three things to know

Finally, time to swap out your old, sad, outdated chair for the latest and greatest! Your old chair broke, or your office is getting renovated, or (worst of all) your last chair was so painful you made a special request.

You are quickly overwhelmed with options, and everyone tells you that their chair is somehow the latest and greatest - even though they all look preeeeettty much the same.

My last three years have been spent constantly searching for the latest and greatest in office seating. I have been amazed at how many “solutions” do not align with established research. If you are looking for a chair, here are the three most important things to keep in mind:

#1 - The Importance of a Chair

This cannot be overstated. The average American will spend more than half their life sitting(3) , and most of this sitting happens in an office chair. People are accustomed to investing in their mattresses and in running or athletic shoes, but they will sit more than they stand or lie down: combined. Take your time, educate yourself, and invest in a chair that will support your health!

As a business leader or interior designer, this is also critical. Of all office furniture and equipment, the office chair makes arguably the largest impact on the employee experience. Academic researchers agree:

“The office task chair is routinely misunderstood, undervalued and probably the least appreciated asset employers purchase”(1)
“The physical environment inside the company, especially the chair and desk, had a great influence on satisfaction.” (2)
“The chair and desk have a great influence on the satisfaction of the office environment” (2)

#2 - The Basics: A Backrest

The first and most important thing about backrests: have one.

People fed up with a terrible office chair often decide that an exercise ball will solve all their problems. Researchers Gabriela Luna-Ávila and Elvia González-Muñoz (4) found that without a backrest your body will fatigue and slouch within ten minutes. Another study found that chairs with back support are far superior to those without (5). Exercise balls are great for a 10-15 minute exercise break, but are a terrible chair substitute.

The next thing to know about backrests: the taller the better. One of the classic academic papers on chair ergonomic evaluation (Occhipinti, Colombini, Molteni, & Grieco, 1993) (6) names backrest height as one of the five most important factors to chair comfort. A higher backrest may be more expensive, but it is worth the investment.

The final key to backrests is the shape and contours, another one of the five most important factors mentioned by Occhipinti et al (1993) (6). This is a more subjective factor, and the old- fashioned “sit test” is the best way to know if a chair fits you well.

#3 - The Secret Sauce: Trunk-Thigh Angle

Recent research supports the idea that healthy sitting is moving among different good postures rather than a single “perfect” posture (7). But one posture factor is supported by robust research, yet many people are unaware of its importance until they visit a physical therapist: the “trunk-thigh angle”. This is exactly as it sounds; the angle that your hips take between your upper body and your thighs. Most people associate good posture with a 90-degree angle, or “sitting up”. This is NOT the case (8)!

The ideal trunk-thigh angle for sitting is between 110-135 degrees (9). In an office environment, sitting at 135 degrees and looking forward strains your neck, so 110 degrees is ideal (10). If you go to a physical therapist with back or neck pain, they are very likely to get you a wedge (pictured right) to sit on. Very few office chairs have that functionality built in. The easiest way to tell if your chair has a good trunk-thigh angle: sit in the chair and see if your hips are above your knees (it will only be slight).

Just how important is this angle? Keegan (8) named the trunk-thigh angle “the most important postural factor in the causation of low-back pain in sitting”. Another study found evidence that sitting on a slightly declined surface lowers the pressure on the spine (10).

Conclusion:

If you are looking for a new chair, here is a checklist to make sure you get the right one:

  • View your chair as an investment, not an expense

  • Make sure the chair has a backrest: the taller the better, and try it to see if the contours are supportive and comfortable!

  • Check your trunk-thigh angle; are your hips above your knees when you sit?



Citations:

(1) Heller-Ono, Alison. (2019). A Chair Assessment Model for Organizational Benefit, Safety and Asset Management: Volume IV: Organizational Design and Management (ODAM), Professional Affairs, Forensic. 10.1007/978-3-319-96080-7_10.

(2) Mitsuya R., Nakamura K., Sugita T., Ozawa N., Yaita T., Kawai T. (2019) An Ergonomic Evaluation of Elevating the Work Desk: The Relationship of Sitting Work with Standing Work. In: Goonetilleke R., Karwowski W. (eds) Advances in Physical Ergonomics & Human Factors. AHFE 2018. Advances in Intelligent Systems and Computing, vol 789. Springer, Cham

(3) Jin S., Kim S., Chang S.R. (2019) The Effect of the Lower Extremity Posture on Trunk While Sitting. In: Bagnara S., Tartaglia R., Albolino S., Alexander T., Fujita Y. (eds) Proceedings of the 20th Congress of the International Ergonomics Association (IEA 2018). IEA 2018. Advances in Intelligent Systems and Computing, vol 820. Springer, Cham

(4) Luna-Ávila, Gabriela & González-Muñoz, Elvia. (2019). Comparison of Posture, Comfort and Satisfaction Between a Dynamic Seat and a Seat with Ergonomic Criteria. 10.1007/978-3-319-94706-8_57.

(5) Cho, Il & Park, Si & Park, Jonghoon & Kim, Tae & Jung, Tae & Lee, Hyun. (2015). The Effect of Standing and Different Sitting Positions on Lumbar Lordosis: Radiographic Study of 30 Healthy Volunteers. Asian Spine Journal. 9. 762. 10.4184/asj.2015.9.5.762.

(6) Occhipinti, E., Colombini, D., Molteni, G., & Grieco, A. (1993). Criteria for the ergonomic evaluation of work chairs. La Medicina del lavoro, 84 4, 274-85.

(7) Slater, Diane & Korakakis, Vasileios & O'Sullivan, Peter & Nolan, David & O'Sullivan, Kieran. (2019). “Sit Up Straight”: Time to Re-evaluate. Journal of Orthopaedic & Sports Physical Therapy. 49. 562-564. 10.2519/jospt.2019.0610.

(8) Jin, Sangeun & Kim, Seulgi & Chang, Seong. (2019). The Effect of the Lower Extremity Posture on Trunk While Sitting: Volume III: Musculoskeletal Disorders. 10.1007/978-3-319-96083-8_22.

(9) Keegan, J. J. (1953). Alterations of the lumbar curve related to posture and seating. JBJS, 35(3), 589-603.

(10) Harrison, D. D., Harrison, S. O., Croft, A. C., Harrison, D. E., & Troyanovich, S. J. (1999). Sitting biomechanics part I: review of the literature. Journal of manipulative and physiological therapeutics, 22(9), 594-609.

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