Chair Ergonomics

Discussion in 'Miscellaneous' started by Amazoniac, Feb 10, 2016.

  1. Amazoniac

    Amazoniac Member

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    Humans,
    pboy,

    Seat
    • Usually the flat ones offer more freedom to move. Some seats are carved, which is cute but it's not good for an everyday chair. That cute feature becomes a bothering feature during use.
    • Look for the ones that are slightly tilted backwards because it gives a sense of security that you won't slip from the chair, so you don't need to keep compensating by forcing yourself back to it.
    • A smooth curve by the end that's close to your knee tends to release some discomfort that might appear if you opt for sharper end ones.
    • Regarding size, depending on the part of a chair, the industry have to use extreme percentiles to be able to manufacture in large scale and fit most people. The problem is that in some countries obesity or bigger butts are more common; since the arm rest are usually attached to the seat, if you have to manufacture a seat that fits nearly everyone in those countries, you'll be left with an open wing prepared to fly if you are a tiny person. Even if you are a woman with more curves, you'll have that problem because your shoulder won't align with the arm rest.
    • Of course it has to be smaller than the length of your thigh and the seat leveled slightly below your knee.
    Back
    • I prefer smaller ones rather than a semi-throne, racing car-like back. They usually force your spine to fit their alignment in a bad position.
    • Some of them are made with a soft mesh and that tends to be problematic because as soon as you rest your back, the mesh will deform excessively with the weight and constrict your body, suffocating and leading to instant death.
    • It's crucial that you have a free space for your butt, they solve that by leaving an open space between the back and the seat. When we seat, our butt ocupies a larger area so you need to have that free space, otherwise it will deform your posture/spine while you're sitting.
    • Regarding material, some people prefer those meshes because they are cooler (literally).
    Arm rests
    • For the reasons that I mentioned previsouly, arm rests that are attached to the back are better. Some of them are attached to the base of the chair which is fine too (especially if you can ajust the height).
    • They cannot lock you inside the chair. The better ones are the ones that don't have a closed perimeter, they should be a slight hozontal curve (profile), that way you'll have room for your legs to move freelythebananagirl.

    The better chairs are usually not sold as ergonomic chairs because they are simpler, and simpler is subtle in details, and that how it should be. Constantly noticing a part of an object is the first sign that it was poorly designed.
    This post is probably going to be edited more times because I won't remember everything. And please add anything that I forgot/don't know.

    here's a decent one:
    Diffrient World Chair | Ergonomic Seating from Humanscale
     
  2. DaveFoster

    DaveFoster Member

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    Good post. Deadlifts help strengthen the lumbar as well.

    Lowering inflammation is key as well.
     
  3. OP
    Amazoniac

    Amazoniac Member

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    In general, when things go bad, engineers kill people fast, designers kill them slowly..
     
  4. CoolTweetPete

    CoolTweetPete Member

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  5. OP
    Amazoniac

    Amazoniac Member

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  6. Liubo

    Liubo Member

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    You already know my views on chairs, amazoniac! Haha. I'm a floor person : )
     
  7. NathanK

    NathanK Member

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  8. OP
    Amazoniac

    Amazoniac Member

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    I forgot to add that the best chair arms are about 2/3 the seat depth. The rest is completely unnecessary as the arms don't rest on it and only serve to prevent people from getting closer to their desks.
     
  9. 2thecloudsabove

    2thecloudsabove Member

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    For desk time, nothing beats the state-of-the-art on back health and ergonomics.

    [​IMG]
     
  10. OP
    Amazoniac

    Amazoniac Member

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    Since you can't rest your back and your knees at the same time, it looks like its purpose is to change your posture often. These were popular a long time ago and stopped being used because of the eventual problems that tend to appear from prolonged use.
    The Problems With Kneeling Chairs | YogaBack
    The Problems With Kneeling Chairs
    by Dennis Zacharkow, PT
    © 2015

    A kneeling chair is a unique design of a forward-sloping seat without a backrest. In order to keep the buttocks from sliding forward on the seat, the sitter's legs are supported just below the knees by a large padded support. As a result, the sitter's lower legs are tucked under the seat. This sitting posture results in a more open thigh-to-trunk angle than when using more conventional chairs, along with a greater degree of knee flexion.

    Diffrient (1984) commented that the kneeling chair would most benefit those individuals who wanted to work in a forward-leaning posture over a desk. Among the disadvantages of this design, Diffrient mentioned that without a backrest one is unable to assume a backward-leaning posture and obtain back support. Therefore, the sitter is limited to forward-leaning and upright postures.

    Diffrient (1984) also mentioned the potential problems of constant pressure on the shins, and the fact that the sitter's feet are in a cramped position. Thompson (1985) also referred to the potential problem with pressure on the knees, along with the awkward positioning of the toes.

    The possibility of increased discomfort in the knees and lower legs suggested by Diffrient (1984) and Thompson (1985) was also noted in the comfort ratings of university students after two hours of sitting in a kneeling chair (Porter and Davis, 1983).

    An extensive study by Drury and Francher (1985) involved the comfort ratings for a kneeling chair with a 15-degree forward slope to the seat. The kneeling chair was evaluated over a 2 1/2 hour session. Five one-half hour training periods were previously given to all the subjects in order to adjust to the kneeling chair.

    The comfort ratings showed that the greatest discomfort with the kneeling chair involved the legs and knees, and to a lesser extent the back and buttocks. For some individuals, a major problem involved difficulty getting into and out of the kneeling chair.

    According to Drury and Francher (1985):

    "Despite the training given in use of this chair, the overall comfort was not particularly good. Results were worse in overall magnitude than the earlier prototype conventional chair tested, and discomfort increased with time-on-task rather than remaining level.

    Body parts affected by the novel chair were primarily the legs, particularly knees and shins. Knee discomfort, presumably from the acute knee angle, was noticeable. For this increased leg discomfort there was little or no corresponding decrease in back discomfort. Although subjects had the theory of the chair explained to them during training and tried to sit with a lordotic spine, they often slumped forward to give a kyphotic curve instead."

    Bridger (1988) found a common postural adaptation to the kneeling chair to be an "erect slumped" posture. In the "erect slumped" posture, "the trunk has tilted rearward about the hip joints, which have extended. The upper body is erect but the spine is flexed" (Bridger, 1988).

    Another description for this "erect slumped" posture is a "postural depression," which refers to the hinging forward of the front of the rib cage towards the pelvis (Anderson, 1951; Zacharkow, 1998). (See Figure 1.)

    [​IMG]

    The same "postural depression" occurs when leaning against the backrest of most chairs, and also when leaning forward improperly.

    Proper support to the lower thoracic spine is the only way to correct this main postural fault of sitting: the "postural depression" or hinging forward of the front of the rib cage towards the pelvis (Zacharkow, 1988, 1998).

    References
    • Anderson, T.: Human Kinetics and Analysing Body Movements. London, Heinemann, 1951.
    • Brider, R.S.: Postural adaptations to a sloping chair and work surface. Human Factors, 30(2): 237-247, April 1988.
    • Diffrient, N.: The Diffrient difference. Leading Edge, 5: 41-59, June 1984.
    • Drury, C.G., and Francher, M.: Evaluation of a forward-sloping chair. Applied Ergonomics, 16: 41-47, 1985.
    • Porter, J.M., and Davis, G.N.: An assessment of alternative seating. In Coombes, K. (Ed.): Proceedings of the Ergonomics Society's Conference 1983. New York, Taylor and Francis, 1983, pp. 202-203.
    • Thompson, D.A.: Where I stand on seating. Human Factors Society Bulletin, 28: 1-2, September 1985.
    • Zacharkow, D.: Posture: Sitting, Standing, Chair Design and Exercise. Springfield, Thomas, 1988.
    • Zacharkow, D.: ZackBack Sitting. Rochester, ZACKBACK International, 1998.

    Evaluation of a forward-sloping chair - ScienceDirect

    Rocking chairs would require you to stabilize them, which is distracting.

    I also forgot to add that some seats don't depress and are tough enough to compress (lit rhyme) the perineum area between your legs, it's almost as if you were on a bad bike saddle the entire time. It's one more thing to pay attention to.

    It's puzzling how chairs haven't converged on some consensus already, people have been sitting since.. always.
     
  11. Waynish

    Waynish Member

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    I've owned several kneeling chairs from Hag and gaming chairs, and used to sit cross legged on an Ikea table... I think the optimal is a combination of two that the chair would let you switch between. 1) a flat surface with no support that encourages upright posture and a straight spine, and 2) reclines to nearly laying down such that the spine feels straight, but you could sleep if you wanted to.
     
  12. x-ray peat

    x-ray peat Member

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    Anyone into reclining. You need to set up your monitor so that it is up high and have it big enough so that you can increase the font size so you can read it, but there is evidence that this is the best seating posture for your back.

    [​IMG]
    "
    In this study, the patients assumed three different sitting positions: a slouching position, in which the body is hunched forward as if they were leaning over a desk or a video game console, an upright 90-degree sitting position; and a "relaxed" position where they leaned back at 135 degrees while their feet remained on the floor.

    The researchers then took measurements of spinal angles and spinal disk height and movement across the different positions.

    Spinal disk movement occurs when weight-bearing strain is placed on the spine, causing the disk to move out of place.

    Disk movement was found to be most pronounced with a 90-degree upright sitting posture.

    It was least pronounced with the 135-degree posture, suggesting less strain is placed on the spinal disks and associated muscles and tendons in a more relaxed sitting position."

    BBC News - Sitting straight 'bad for backs'
    Why Sitting Reclined Is Better For You
     
  13. DrJ

    DrJ Member

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    Agree about the deadlifts. Doing deadlifts removed all lower back pain and issues I was having even though I often sit for 8+ hours a day coding. A good defense for when you can't have your chair of choice.
     
  14. OP
    Amazoniac

    Amazoniac Member

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  15. OP
    Amazoniac

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    As you know, it's ideal for a desk to be adjustable in height. When this is not possible, I would be wary of models with drawers because they constrict space, yet it can be compensated by increasing the size of the desk. If they is positioned laterally, doing this won't be a problem; however, if they're placed between your lap and the top plane of the desk, the compensation can lead to uncomfortable postures. Your arms will be elevated while the arms of the chair won't follow, attempting to correct this by sitting closer and dispensing its arms likely won't work because the chair's will prevent this, and if they doesn't, desks don't usually have enough depth to maintain an adequate distance between your head and the screen, so you'll be shortening this distance further. What's likely to happen is to stop midway with T-rex forearms resting on the edge of the desk. Either way, widening arms to minimize the issue means that the hands will rotate but the keyboard won't, try to do it and you'll realize the problem that arises. Rudimentary figures suffice to illustrate how adding a drawer can complicate things:

    upload_2019-11-15_7-18-42.png
    Unread source.


    This person will be hospitalized soon:

    upload_2019-11-15_7-19-0.png

    In terms of optimal height, the table's has to follow that of the chair, which will adjust based on the person, not the opposite. Regarding depth, it's better to have extra space so that it's not limiting.

    - European Sitting Championship: Prevalence and Correlates of Self-Reported Sitting Time in the 28 European Union Member States :ss


    - Chair legs and stability | physics.stackexchange.com


    I would also pay attention to the materials used in these (chair, desk, etc). Many of them contain metallic parts that can have abverse effects in terms of EM radiation from the office. Others could've been lined with suspicious ones that release with use.


    Tarmander, my enemy, suggested somewhere the use of projectors to reduce eye strain. This can be interesting, but it's another area that I would be wary. These images don't tend to be well-defined, people are tempted to turn the lights off to improve them but the contrast can be stressful, there has to be unity in lighting. Head tilt is something to pay attention to. I've been suspecting for a while now that reading with the head on the horizontal position has a different effect than the traditional and immersive head-down (desk surface color and texture can be impacting here as well because it's what surrounds the area of focus). There might be minor changes in brain nourishment depending on the position of the head that could affect cognitive performance.

    It's difficult to have an image on a wall of a room without avoiding the elevation of head, rising the chair along isn't much simple, it's likely for the person to end up in a situation that's akin to sitting on the first rows of a mowie theater. An attempt to mitigate this is through inclining the chair so that the eyes are leveled with the top of the image, but then we don't know the consequences in terms of cognition, extending the body might also not be compatible with an alert state. It's just something to be mindful because it can change how you process information.
     
  16. GorillaHead

    GorillaHead Member

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    Any chairs and or desks you can link or recommend? I suffer from slouching and forward head posture. I am trying to reverse it. It’s going to take a long time to reverse 27 years of this.
     
  17. OP
    Amazoniac

    Amazoniac Member

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    The one from the original post looks good to me (but you can find other options that have these features with varying prices). Here's a setup including it:

    upload_2019-11-15_8-40-18.png

    No transversal bars or dispensable structural parts that clutter and get in the way of free movement; simple and clean, how it's supposed to be. If the metallic pieces are concerning, there are improvised versions with wood:

    upload_2019-11-15_8-41-12.png
     
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