Are Office Chairs Really “One Size Fits All”?

The short answer is no. Because people come in such a wide range of sizes, the 5 inches of height adjustment available in office chair can’t possibly accommodate all people. So, the real question is: Why do all office chair companies offer only one chair size? The answer seems to be convenience. Unfortunately, it’s corporate convenience rather than consumer convenience.

The gas cylinder under your office chair’s seat that allows fingertip control of your chair’s height is an engineering marvel. Patented by John Wang in 1989, it quickly captured the market because its simple design made it both reliable and extremely cheap to manufacture at scale. Even better, the control interface is so intuitive that we scarcely notice it; we just adjust our chair’s height and get on with our day.

The basic design employs compressed nitrogen gas to allow smooth, continuous height adjustments using a simple lever mechanism and also allows your chair to rotate freely on just 5 ball bearings. How successful was this design? Over a billion have been manufactured to date, with tens of millions more added every year.

But despite this design’s mechanical brilliance and commercial success, your office chair’s gas cylinder has one deal breaking limitation. It turns out that the “cylinder within a cylinder” design at the heart of this mechanism restricts its maximum extension to always be less than half its compressed height.

Unfortunately, because people come in such a range of sizes office chairs need to provide a seat height that ranges from 18” off the ground for petite people to 29” for basketball players. This is a range of almost a foot. Unfortunately, while gas cylinders with a 10” range are available, these cylinders had a compressed length that corresponds to a lowest chair height of about 22”, too high for almost half of adults. And this is a problem without a solution: because of its elegantly simple internal workings, physics doesn’t permit a gas cylinder to more than double its length.

So how does the office chair industry handle this inherent limitation of gas cylinders? The surprising answer is, by ignoring human anatomy. Here’s the scoop: The crucial dimension for ensuring that a chair fits one’s body is one’s popliteal height, that is, the distance from the floor to the back of your knee when seated with your feet are flat on the floor.

Here’s a diagram of how popliteal height is measured.

But please don’t take this diagram is an endorsement of this posture as we discuss below. But note that “Most people are unable to sit erect in the 90-degree posture for long periods and soon adopt a slumped posture”¹

Population surveys find that ninety-five percent of Americans have popliteal heights of between 13.1 and 21.3”, so at a bare minimum an 8” range of seat heights is required for office chairs to have a chance of fitting most people.² The 5” range provided by the typical ergonomic office chair is only 60% of what human anatomy requires.

And it gets worse. The above analysis assumes that people sit with ankles, knees and hips at 90 degrees, a posture comes with a host of anatomic problems that make it uncomfortable, and unsustainable, as a seated posture for any length of time. We’ve known since Madal’s pioneering paper in 1981 that human hip anatomy makes sitting with one’s knees lower than one’s hips a far more natural, and comfortable, spinal posture.³ This diagram from Mandal’s paper demonstrates that sitting with the knees lower than the hips allows the lumbar spine to assert its normal lordosis; in this case a seat height of 72 centimeters (28 inches) on the far right is required for optimal posture.

Exactly why this is so requires a brief detour into human anatomy books, but here it is in a nutshell. Because the psoas muscle originates from the five lumbar vertebrae and inserts on the femur, the hip must be extended past 90 degrees to allow the psoas to pull the lumbar vertebrae into their normal lordotic posture. The next diagram is derived from a careful compilation of many lateral x-rays in a single subject compiled by Dr. J.J. Keegan in 1953.⁴ It shows the hip at a variety of angles, but note that the middle posture (“C”, labeled “NORMAL”) allows for the most natural spine configuration while sitting. 

 

All this anatomy means that a range 18” to 29” in seat height is required for people to sit with their knees comfortably lower than their hips. The total required range is thus 11”, over twice that that any single gas cylinder can provide.

Two thousand years ago the Greeks developed an uncanny ability to imagine mythological punishments, but none were more original that of Procrustes. In this story, Procrustes generously offered to provide a bed for the night for weary travelers who happened by his lair. Unfortunately for his guests, however, if they proved too tall for his bed Procrustes would amputate the excess length, and if the guest was too short Procrustes would stretch them until they died; nobody ever fit the bed exactly.

The insistence of contemporary office furniture companies that one size of chair will fit all comers eerily recalls Procrustes’ methods. Yes, these chairs provide 5” of height adjustment and so can be adjusted to fit many people. But woe to those of us who are short or tall; if too short we’re expected to put a phone book under our feet and if too tall to put it under our bottoms.

But it needn’t be like this because the fix is readily available. Gas cylinders are manufactured in various sizes so it would be easy for office furniture companies to provide chairs in two sizes by simply using a short gas cylinder to create short chairs and tall gas cylinders to create tall chairs. And yet no company has taken this simple step.

Except one.

Our little startup, QOR360, felt so strongly that healthy sitting required a chair that fits one’s anatomy that we provide our chairs in two size ranges. As we implemented this approach, I came to understand why every other chair company made do with selling one size of chair. While making two different sizes of a chair was easy (just use a tall or a short gas cylinder), explaining to people how to pick the right size of chair, and handling the inevitable exchanges required when the initial size wasn’t right, turned out to take a bit of effort. Eventually we found that a short video that explains chair sizes eliminated most of the confusion caused by our “two sizes of chairs” approach:

Will other office chair companies follow our example? Not yet. But it often happens that innovation comes from small startup without the baggage that comes with a long history in the business. Eventually “Big Chair” will come around. But in the meantime, if you’re looking for a chair that fits you, we’re your company.

 

¹Introduction to Ergonomics, R.S. Bridger, pp 61.

²Gordon, C. C., McConville, J. T., & McManus, I. (1988). Anthropometric detailed data tables (Interim Report, March 1989). The Ergonomics Center of North Carolina. 

³Mandal, A. C. (1981). The seated man (Homo Sedens): The seated work position. Theory and practice. Applied Ergonomics, 12(1), 19–26. 

⁴JJ Keegan, Alterations of the Lumbar Curve Related to Posture and Seating, Journal of Bone and Joint Surgery, 1953