High back chair dimensions

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This topic contains 23 replies, has 7 voices, and was last updated by  kclark66 8 years, 5 months ago.

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  • #37300

    sarahjaneobrien
    Participant

    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?

    Regards

    Sarah-Jane

    #42484

    humanics
    Participant

    >> 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, CPE

    http://www.humanics-es.com

    #42487

    Ergohead
    Participant

    High back?

    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!

    #42489

    humanics
    Participant

    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, CPE

    http://www.humanics-es.com

    #42490

    Ergohead
    Participant

    Rani

    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.

    #42491

    humanics
    Participant

    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.

    Rani

    #42492

    humanics
    Participant

    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…

    #42493

    Ergohead
    Participant

    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.

    #42495

    Ergohead
    Participant

    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.

    #42496

    JohnR
    Participant

    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!

    #42494

    Ergohead
    Participant

    John

    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?

    #42499

    shanng
    Participant

    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! Shann

    #42501

    sarahjaneobrien
    Participant

    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-Jane

    #42502

    humanics
    Participant

    >>> 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.

    http://humanics-es.com/yamaguchi.jpg

    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, CPE

    http://www.humanics-es.com

    #42500

    humanics
    Participant

    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.

    Rani

    #42503

    Ergohead
    Participant

    Rani

    Not a heckler, and not trying to disparage. It just seemed to me that with your mention of Grandjean, you were equating reclining backrests with long backrests. I oftentimes recline on chairs with short backrests, even ones where the backrest stays vertically fixed.

    Personally, I still see little physiological benefit to a long backrest – but for those who do, I must say I am impressed with the Hoganasmobler line because of what I perceive as a movement towards reclining benefits due to their combination of recline in association with a floating seat pan. I have never personally sat on one but am mentally intrigued at this combination. However, I am equally impressed with Ronald G. Kleist’s Swing Chair by SmartMotion Technology, Inc., as it seems to be accomplishing the same physiological benefits as Hoganasmobler, and making my point, not necessarily with a long backrest.

    http://www.posture.co.uk/hoganasmobler.html

    #42504

    humanics
    Participant

    Just shows we all have our own ideas about what we are talking about. I don’t think of the SwingSeat as having a low back (disclosure: I previously consulted for them) and it is one of the chairs I think of that may enable users to assume forward seatpan tilt without having to fight the chair.

    In the end though we were asked to help her decide between standard and high back versions of one specific but unknown chair model. All we really know is that a lot of Call Center employees prefer this chair and that it is apparently more comfortable.

    Rani Lueder, CPE

    #42505

    JohnR
    Participant

    This just reinforces my initial feelings to steer clear of this debate, and so I shall (almost) – suffice to say that a discussion of this nature can only be satisfactorily concluded face to face – a forum such as this (and good as it surely is) inevitably fosters misunderstandings and misinterpretation, sometimes resulting in inappropriate responses. As someone once said “Language (on its own) is a very poor form of communication.”

    (But just one further comment: Rani, I entirely agree with you re the need for call centre workers to lean back whenever they have the opportunty, which should be during converstaions with the caller. There are of course lots of ifs and buts and riders to this (including the issues Rani has raised because we don’t know what the dimensions are of the back rests under consideration), and the only way to answer your questions, Sarah-Jane, is probably to get a consultant in. If as it appears, you are in Australia, you could do worse than contacting WorkCover and Dave McFarlane (is he avoiding this spat as well?).

    #42535

    admin
    Keymaster

    John,

    I haven’t been avoiding this spat; I have been down in Melbourne (aka “Rain-in-the-face city” in mid-winter) helping my mother to celebrate her 91st birthday. In actual fact I have read this thread with interest.

    This is a good question!;

    What IS the ideal shape for the backrest of an office chair?

    The first question I would ask myself is this; “When does a seated worker mainly use the backrest?”; not usually during keyboard work according to some pundits. People leaning forwards often make little use of the backrest even if their lower back is lordotic i.e. “a bolt upright posture” (indeed especially when it is perhaps?).

    My impression is that low backrests are intended to favor a forward pelvic tilt to encourage lordosis of the lower back. Tilting the seat and backrest position does not usually determine pelvic tilt as the task needs usually override such chair design factors (please see footnote).

    Secondly should we really be aiming for comfort for forward-leaning workers or those who prefer a laid-back posture and/or those are leaning back for a rest? My guess is that high backrests would only be useful in those situations. If we are going to go that far, why not go the whole hog and provide a headrest as well? That might then become the new managerial status symbol!

    Tom Bendix noted that people trying to rest after prolonged sitting often prefer to adopt a kyphotic posture i.e. “a slumped posture” (Bendix, 1987, page 126) to relieve the discomfort in the posterior section of the spine (this is presumed to be due the compression on the facet joints in that area). This suggests that maybe we should cater for the backward-leaning worker who wants to recline.

    Can we design a backrest that does both? Short of providing some sort of bean-bag padding or an inflatable back support instead of firm padding I think that this would be close to impossible. Anyway, I might possibly be a bit old-fashioned on this issue but that is my two bob’s worth.

    Regards,

    David McFarlane

    Ergonomist, WorkCover Authority

    New South Wales, Australia

    Reference

    T. Bendix, (1987),

    #42825

    kclark66
    Participant

    HI,

    I have been reading the forum on the height of seat backs. I have a tangent question. DaveMac commented about kneeling chairs only being good for use at 20-minute intervals. I have used kneeling chairs before and agree that my back does feel better. However, I have bad knees and they easily become aggravated after 20-30 minutes of using the chair. My question is, how do we decide which body part should be addressed in the seating adjustments?

    Kim Clark, PT

    #42829

    JohnR
    Participant

    I think you probably know the answer to this question, and it follows standard ergonomics advice to first assess relevant factors; e.g. which problem creates the most severe symptoms, and which mode of working might lead to the most severe outcomes? Once that is understood, priorities can be established, but inevitably ergonomic splutions will always embody an element of compromise; but that is why the questions are asked of experienced professionals – in order to get the benefit of their knowledge and experience. If it were a simple answer, then human factors specialists would not be required.

    What is clear is that we should all be changing posture as frequently as possible, and workers should be advised of this need and of the various ways in which they can adjust their seating to benefically suit different postures and work activities. In my view 20-30 minutes ‘constrained’ in one posture in a kneeling chair is likely to produce problems. The chairs were in any case originally intended to be used in a manner that allowed, for example, the right leg to be stretched out while support is gained by the left, and then relieving this by changing legs etc. I personally believe that 10 to 15 minutes on a kneeling chair to be beneficial but enough!

    #42826

    JohnR
    Participant

    Dave,

    I wonder if your comment below actually serves to make my point – that misunderstandings can easily arise in these forums (fora?):

    “Though Rani is in LA and some of our expats seem to be trying to take over Hollywood and Malibu we are separated by the Pacific Ocean as far as I know!”

    If this was directed at my suggestion that you should be contacted for consultancy work, I thought I was directing to you not Rani, but SarahJane (who I believe is in the Antipodes); but hey, why don’t we all get together somewhere. I had been hoping to get together with everybody in Las Vegas for the Conference, but never seem to get my act together in time to block out the dates from my diary; anyway, enough of my problems.

    #42833

    admin
    Keymaster

    Kim,

    My standard advice on saddle chairs might help you. It is as follows;

    1. The height of a saddle chair should permit the worker to assume a straddle position with both feet firmly planted on the floor. A semi-resilient mat (such as a rubber mat) should be provided if this causes the worker to get sore feet. The height of the work bench should then be adjusted so that the worker can work comfortably (usually this is near elbow height for handling small objects).

    2. Workers seated on saddle chairs should be instructed to change position (between sitting and standing) frequently often enough to prevent any feelings of discomfort or pain. (Each individual will know best how long they can remain comfortable and pain free in any position.)

    3. Work procedures should be designed to ensure that the worker does not have to stand continuously for more than 30 minutes or sit continuously for more than an hour (as per Van Wely, 1970) in any type of chair and not more than 20 minutes in a saddle chair.

    4. If a worker has a leg muscle spasm the angle of the hips when he or she is seated should be decreased to 90 degrees or less. A worker with this problem should not be provided with a saddle chair. The advice of an occupational therapist should be sought when selecting chairs and cushions for a worker with leg muscle spasms.

    Regards,

    David McFarlane

    Ergonomist, WorkCover NSW

    Postscript; Kneeling Chairs versus Saddle Chairs

    Tom Bendix has pointed out that the original kneeling chairs were designed it with the aim of improving the occupant

    #42836

    kclark66
    Participant

    Dave,

    Thanks for your answer. I appreciate the positive feedback. I think I’ll have to try out a saddle chair. I have never used one.

    Kim Clark, PT

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