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Thread: What is DUMP, when relating to a wheelchair?

  1. #1
    Senior Member forestranger52's Avatar
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    What is DUMP, when relating to a wheelchair?

    What is dump, when relating to the adjustment of a manual wheelchair?
    And just what exactly does it do? I'm thinking that the measurement of 80, 85, 90, must be the degrees of the bend of the knees. Isn't it better to lead with your toes rather than your knees.
    Thanks,
    MAC
    C 5/6 Comp.
    No Tri's or hand function.

    Far better it is to try mighty things, to win glorious triumphs, even though checkered by failure. Than to take rank with those poor spirits who neither enjoy much or suffer much, because they live in the grey twilight that knows neither victory or defeat.

    Teddy Roosevelt

  2. #2
    Mac,
    here is a decent explanation for you.


    Wheelchair Back & Seat Angle

    by Gary Karp,
    The angle of the seat controls stability - and safety - for the rider.
    Your wheelchair seat does not necessarily need to be parallel to the ground. Seats can slope down toward the back. The angle of the seat compared to the ground is known as "seat dump" or "rake."

    Having some degree of seat dump means that more of your weight presses against the wheelchair back making you feel more stable in your seat. People with higher level spinal disabilities gain security and safety with the use of seat dump. Manual riders are able to exert more push with less effort through their arms and shoulders.

    Many chairs have the ability to adjust seat dump. The advent of rigid frame designs for manual wheelchairs, and the modularization of power designs made it easier to adjust the angle of the seat, since the seat support rails are no longer part of the chair's folding mechanism. On a folding wheelchair these rails are fixed, so the seat angle is determined by the position of the wheel axles relative to the entire frame. Raising the rear axles to a higher position has the effect of lowering the rear of the wheelchair and so increases the seat dump. It might also be possible to raise the caster height or use different size casters, achieving the same effect.

    There are tradeoffs for the advantages of seat dump:

    When your knees are raised relative to your thighs, the pelvis rotates backwards with your legs, and the spine is flexed into a rounded shape, flattening out the lumbar curve which plays an important role in the health of your spine. Too much dump, therefore, can increase the risk of scoleosis or disk problems, so should not be used to an extreme. If you experience back pain after using more seat angle, you should adjust it toward a more level angle.
    You need to have sufficient hip flexibility to bend at the waist for added seat dump. Closing the hip angle too much can limit circulation to the legs, already at risk of circulation difficulties from not being used.
    Seat dump can add pressure and shear forces at your sacrum, increasing the risk of skin breakdown. The cushion or chair back can sometimes account for seat dump to minimize contact.
    Finally, a more pronounced seat dump might make it more difficult for you to transfer in and out of your wheelchair.

  3. #3
    dump, my man, is what happens when i eat pork ribs and ice cream
    "All of us are all too stuck strapped to a chair watching our lives blow up..."

  4. #4
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    Quote Originally Posted by forestranger52
    I'm thinking that the measurement of 80, 85, 90, must be the degrees of the bend of the knees. Isn't it better to lead with your toes rather than your knees.
    Thanks,
    MAC
    Yha, this is the angle of the front end... Bigger the angle, the more tucked in your feet are.. This allows you to get closer to things.

  5. #5
    Seat Dump = Front STF Height- Rear STF Height

    Here is a link to a previous post of mine giving my explanation of how seat dump works:

    http://sci.rutgers.edu/forum/showthr...t=76125&page=2

    Front frame angles are typically measured relative to horizontal plane and not the actual bend in the frame...


  6. #6
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    ALONG THE same vein, what are the pros/cons reasons for the varying front angles? (other than the obvious fact that some people may not be able to bend their knees enough .....). My chair is 85 Degrees, but I don;t know what determined that. I actually tend to tuck my feet a little farther back of the footrest these days than I used to, so I can edge up closer to things.
    T7-8 since Feb 2005

  7. #7
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    Some of the stock rigid chairs, Invacare, quickie, etc., only come in standard angles. Ti, and other custom chair makers let you choose.

    Obviously a bigger angle, 90+ degrees, allow you to get closer to things. Helps with transfers.... so I'm told, but also lets you get closer under tables and what not...


    Anyone have a p/c with dump? Thats one of my hates of my p/c.

  8. #8
    Quote Originally Posted by Patonb
    Anyone have a p/c with dump? Thats one of my hates of my p/c.
    mine too. always fallin forward. my DME suggested a wedge under my cushion. have never tried it though.

  9. #9
    Quote Originally Posted by rollin64
    mine too. always fallin forward. my DME suggested a wedge under my cushion. have never tried it though.
    Does your p/c tilt back? That would be a quick fix, or a seatbelt.

    If anyone has a better idea please share.
    Injured May 19, 2006, C4 incomplete

  10. #10

    Powerchair Dump

    Many users feel less stable when sitting in a powerchair--especially when it has power seating. Most manufacturers seem to design powerchairs without differentiating front and rear STF heights. They focus on getting the lowest front STF height possible. Truth is, however, is that the average male has a lower leg length of around 17" (back-of-knee to bottom-of-heel). Front STF heights much lower than 18" will create footplate clearance issues for many of these users. Furthermore, when a powerchair offers power tilt, the logic seems to be: "Design it to have the lowest front STF possible. They can always tilt the seat". If one has to do this most of the time, however, then that low STF height is not really all that low. Since seat dump is not effective unless the back angle still approaches 90 degrees, tilting the seat 5-10 degrees is not the same as having 5-10 degrees of seat dump.

    I am wondering if powerchairs with power tilt systems would be better if engineers focused instead on:
    • Getting the lowest rear STF height possible.
    • Designed the seating under the assumption that most users sit best when the rear STF is a few inches lower than the front.
    But I digress, many powerchairs do allow for adjustment of the amount of tilt in the seat pan as well as the back angle, but it depends on the model. If someone wonders about their particular powerchair, post the make & model.

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