High back chair dimensions
July 17, 2006 at 8:02 pm #37300
Does anyone have the information on the height of a person that would be required to have a high back chair?
At the moment the employees in our call centre all have ergonomics chair, but the minority of taller people have been given higher back chairs and those over 100kgs, given heavier load chairs, as our chairs only take a loading of 110 kgs.
Since the high back chairs are somewhat comfortable, a lot of employees are now asking for them, is there a height requirements that I could use to discriminate?
Sarah-JaneJuly 18, 2006 at 12:06 pm #42484
>> Since the high back chairs are somewhat comfortable, a lot of employees are now asking for them, is there a height requirements that I could use to discriminate?
Goodness, it’s been 20 years since key figures in ergonomics such as Dr. Etienne Grandjean and others started recommending that employees who perform regular or intensive computer work (I think that meant half a day or longer back then) require high backrests as standard practice. I thought this was considered a given by now among ergonomists.
Rani Lueder, CPEJuly 18, 2006 at 4:44 pm #42487
The majority of height differences in humans stem mostly from the differences i n long bone (femur) lengths amongst humans. Much less overall height differences in humans are a result of disparate spinal lengths.
What part of person’s back do you think needs bearing support by the backrest? The shoulders? The Neck? The head?
Grandjean argued more for the reclined backrest over the vertical backrest and its accompanying victorian theory of “proper upright seating posture” than he did for length or body zone support areas. What was his famous angle? 106 degrees? What would this angle have to do with length of the backrest?
I always got the feeling that Grandjean only developed his theory as a national antgonistic response to the German or Swiss (Mandal) theory of a forward tilting seat pan – which negates the need of a backrest, and exposes the so called “need of a backrest” as the negative enablement of kyphosis that it is, by approving an “acceptable kyphotic” support. Seems like another Laize Faire response to anything German or English.
Grandjean had very little to say about what part of the users back should be “supported”. It all just sounds sooooo liberal to me.
If the English say, “Sit up straight!”, the French will tell you to slouch. If the Germans say, “”Tilt forward, and your spine will be balanced with natural lordosis”, the French will say, “Slouch backwards!” And everyone knows that when the Brits say, “Sit up straight!”, that even they know that you will in very short order be “lazy-forced” into a forward slouch with extreme kyphosis. (The famous C-curve) Then, the Brits will blame YOU for not being Victorian enough for your own good.
The Brits: I command!
The French: Hey, chill out!
The Germans: Think!
The Americans: What Ever!July 18, 2006 at 7:56 pm #42489
The point of providing high backrests is first of all to enable help users to better support their upper back and thereby promote postural support – and also reduce the risk of musculoskeletal symptoms in the upper torso. Second of all, it helps them recline further and thereby also facilitates moving through alternative postures.
If you look at the literature, you can see that neck/shoulder pain is the most common musculoskeletal symptom in most workplaces – in a nationwide study I did of the Social Security Administration, I found that on any given day 60% of these employees across the US were reporting moderate to severe neck shoulder discomfort or pain by the end of their workday.
The added cost of high back support is minimal compared to the potential benefit for intensive computer users.
Grandjean was just an example. He was one of the first researchers to investigate these issues and he was widely respected for his introducing the issues. I have considered it the prevailing wisdom of people who track the ergonomics research over the last couple of decades. Back when I started in 1980, high backs were considered primarily of use to denote status – managers got the high backs. A decade later, that approach was generally considered archaic.
Rani Lueder, CPEJuly 18, 2006 at 9:39 pm #42490
Even if your chair were making sudden forward accelerations in intervals throughout the day, I would have a difficult time comprehending how a high backrest would offer much benefit. They don’t seem to be needed on motorcycles. Of course, motorcycles have forward tilt seat pans and appropriately placed foot supports.
The upper back support you speak of is at the expense of, and causative of, leveraged pressure on the lumbar discs and vertebrae that are the fulcrum point for the sacral hinge. Without a forward tilted seat pan causing a healthy pelvic tilt, a high or low backrest only supports a degree of kyphosis. Just because a high backrest touches an upper area of the back, does not mean it is providing any relief to the upper back stresses, which are caused more from arm and hand placement and repetitive motion than by absense of a vertical or reclined “support” touching those areas.
The consensus of the 80′s was correct. A high back chair provides psychological status, and at best, acts as a placebo in lieu of actual physiological benefit. But then again, never understimate the value of faith, or placebo.July 18, 2006 at 10:41 pm #42491
Very few people are willing to use forward seat pan slopes.
That is, in standard chairs that I see in offices that require additional muscle work for proper use.
Tom Bendix’s research found that a few degrees forward can work, but more than that does not.
That said, there are a small number of chairs on the market that enable people to sit in forward slopes without having to fight the chair. But there very few of these.
RaniJuly 18, 2006 at 10:46 pm #42492
Sidebar on this topic, a client of mine (the University of Waseda in Japan) has been performing research on sacral supports at the seat pan level – at the moment to adapt western seating for Zen Buddhist monks. Their research has been finding that sacral supports are much more effective at the seat pan than at the backrest…July 19, 2006 at 12:33 am #42493
I designed a chair with a forward tilted seat pan combined with a free pivoting reclining backrest. If I may say so, it is extremely comfortable. Its effects on lumbar and sacral support are totally outside the Grandjean horizontal seat pan with fixed-recline backrest genre. The missing element in the Grandjean design is a device allowing the user to push his/her lower back into the reclined backrest. A footbrace extended forward of the seat pan works nicely though. Otherwise, a person could have the chair bolted to the floor in close enough proximity to a fixed push away surface (a wall would do) so that the user could push his/her lower body into the reclined backrest. With a push away device such as described above, a lumbar “lump” on the backrest would actually provide a useful lumbar support. Without this, lumbar “lumps” are nothing more than ergonomic hoaxs.
As for the research of Tom Bendix, I don’t think he has considered these types of forward tilts. No muscle work needed here.July 19, 2006 at 12:44 am #42495
It sounds like their research is on the right track.
If the monks don’t insist on sitting directly on the floor, perhaps this kind of sacral support might suffice.July 19, 2006 at 2:14 am #42496
I was going to steer clear of this ‘discussion’, as I believe there are some reasonable points on both sides; but to re-address Sara’s original question -essentially about individual anthropometry used as a criterion for back rest selection – in my view, a broad brush approach is likely to be fine for the majority of workers, but where any difficulties are raised the choice should be made on the outcome of a specific assessment of that individual’s needs in their particular situation and stature is likely to be only one of a number of important elements – a rigid policy is as likely to create problems as solve any.
The high backrest is in my view of primary benefit when the user has the opportunity to come away from keyboard work and lean back – allowing the back rest to take some of the torso weight; but if fixed, it also helps the keyboard operator (whether in Britain, France Germany or Wherever) to maintain a more upright posture when typing.
A footbrace as described by ‘Ergohead’ may work in some applications, but I doubt its general acceptability in normal office environments where floor clearance and space beneath the desk would, I believe, be significant limiting factors; I would also ask whether such a device has any practicable benefit over a decent footrest?
Incidentally, I believe (from looking at some of the early research data a while back now) that Grandjean’s magical back rest inclination angle of 106 degrees actually had a lot to do with the limits of the chair that he was using in those early experiments – it didn’t go back any further!July 19, 2006 at 10:51 am #42494
Your first paragraph is professional sounding and defensively diplomatic. But try to recall Lili Tomlin acting as a 5-year old child rocking in an oversized rocking chair in the early Saturday Night Live skits. The seat pan was too deep, the backrest was too high, but throughout it all, she always managed to tell “the truth”.
Your second paragraph: Pretty bland and vague, and tacitly dismissive of my earlier point that statutory (fixed) support rearward and upward of the lumbar area is problematic at best, especially with respect to the leveraged force this disposition exerts on lumbar tissues.
Your third paragraph: Are you defining a “decent footrest” as any floor supported device capable of resisting the gravitational pull of a user’s lower limbs not supported by the seat pan? Just vertical support? No lateral bracing? Your feet are connected to your lumbar vertebrae, indirectly, wherein your lumbar is supported on conventional chairs by your feet and your butt. Whatever is lacking in foot related support of your lumbar is not going to be correctly taken up with the help of of a fixed backrest, which would only be an attempted solution to a problem caused by the distal inadequacy of proper foot support. It is short sighted to think that the purpose of a footrest is to only support the feet and lower limbs. The wholistic purpose of a footrest for a seated or standing person is to support the upper torso via functional use of the feet.
Your paragraph four: Hadn’t the hinge been invented at the time of his research?July 19, 2006 at 4:23 pm #42499
What a sane response! People are not mechanical robots and all the precise physical measurements are helpful tools but nowhere near the answer to a universal solution. Overriding all these wonderful scientific approaches are the cultural attitudes and upbringing of the person using the chair. Unless there has been specific trauma that demands readjustment to long formed habits it will be an uphill battle to change seating preferences. That of course takes into consideration appropriate desk and chair heights and position of various desk components when operating a computer.
Over the years I’ve tried all sorts of office chairs for myself … from a fixed Windsor desk chair as a high school student (pre-computers) to various types of adjustable models (for & aft tilt pans … thoroughly dislike forward tilts; up & down, backrest back or forward ) I’m now happiest with my present fixed high back chair, with adjustable height (set once correctly and left there) and with 5-star base on castors to move rapidly in and around my large corner desk & along its lateral extensions. I sit up straight to type (without back support and sit back to read. General activities keep me going indefinitely!!!
So, please take note of your clients’ behavioural preferences as well as their measurements and a nifty checklist. Cultural attitudes overide prescriptions every time!! That has proven true in half a century’s experience! ShannJuly 19, 2006 at 5:05 pm #42501
Thank you everyone for your advice. One of the things I need to take into account is that we cannot afford to buy new chairs. The decision is either that we get the current 5 wheel base ergo chairs refitted with higher backs or not for those that require them. My question was, who requires high back chairs, if any?
From speaking to some ergonomists in Sydney and reading your posts, I have come to the conclusion that the high back would be useful if they need to lean back to read. But my employees are call timed, call monitored and measured against call numbers, they don’t read any paperwork, and don’t write anything down. All their work is on headsets and the computer screen. When they break, they are walking around or doing stretches. Their upper backs don’t need to be supported with a higher back if their lower back can be supported by back rest.
Therefore I have come to the conclusion that there is no need to discriminate the taller employee and get their chairs modified, if there is no need to recline. We have lots of ‘chill out’ zones in the call centre where employees can recline, and they are encourage when breaking to walk around, and use these areas.
Sarah-JaneJuly 19, 2006 at 5:20 pm #42502
>>> The high backrest is in my view of primary benefit when the user has the opportunity to come away from keyboard work and lean back.
John, thanks for posting. I rather wish I hadn’t stepped in as well, since the thread may confuse visitors who are trying to understand the issue. And it’s not fun communicating when it feels like a heckler is looking for opportunities to disparage the others.
I didn’t mention Grandjean’s recline angle for the reason you mentioned – it was limited by the chairs used at the site. Reminds me tangentially of how Mandal used to say that the 90 degree knee angle recommendation was an artifact of Akerblom having extremely short legs. Back on topic, experimental studies have their own limitations, including the dimensions of the text fixture.
I mentioned Grandjean only with respect to high backs because it seems to me that he was the first one to recommend them for intensive computer users.
I’m not trying to defend Grandjean, but I like to track where things came from. Grandjean was an early proponent of the importance of postural support and in neutral postures. For example Yamaguchi’s study, is only described in Grandjean’s ergonomics of the home book. I uploaded it for the purpose of discussion on this thread. Neutral postures result from a broad range of factors… While the seating research often contradicts what we expect to find (e.g., that forward sloping seats or backrest recline promoted lumbar curvatures), it also plays out in other ways.
It feels a bit like we’re arguing about how many fairies dance on the head of the pin, since we each have our own idea about what we’re saying – and the applications are quite different. That said, far as I’m concerned, call center employees need to be able to recline as much as anyone… they may have fewer opportunities to do so, but that just makes these opportunities more important. Even if we can only recline 5% of the workday, this opportunity to lean back is critical. It’s central to the idea of recovery – and off-loading forces throughout the day.
Rani Lueder, CPEJuly 19, 2006 at 5:35 pm #42500
Sarahjane, that brings up the other question – how high is high? If I understood your question, you are asking us how tall people should be (as an index of torso length) to provide a high backrest – but you gave us no dimensions of the standard and high backrests you are considering – which can vary a great deal between models.
Another issue in play… the backrest should be adjusted to the height that best supports the lumbar spine. The range of backrest height adjustment and the location of the lumbar are part of the equation also.
In the end though my response reflected your comment to the effect that a considerable number of employees at your company wanted the high backrest and that you are attributing their requests to the greater comfort of the chair.
To me, that’s a no brainer. If a high back chair makes that much of a difference where you and they perceive that it is more comfortable and presumably more supportive, my feeling is that you are probably going to save a lot of money (and retain more employees) in the end by just standardizing on this kind of chair.
On top of that, from a psychosocial perspective, you are allowing them to have a small amount of participation in a job that provides minimal job control – and at the same time showing them that management cares about how they think and feel. All that for what should be a fairly moderate difference in costs between the two types of chairs. It may add up, but then again the costs not to do so are also expensive.
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