Sitting Postures
There are three recognized seated working postures that are consistent with
neutral body positioning. They are: Declined, upright, and reclined. To avoid fatigue and slouching, an
operator should understand how to use and vary their sitting posture throughout the day.
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Declined
The declined posture can be used to reduce strain on the back, and it can help the operator to avoid slouching by
making it easier to sit up straight. This is because sitting with the knees below the hips places the pelvis in an
orientation that supports a healthy posture of the spine. This is not as effective for generously proportioned individuals, and it
is recommended that they consider the reclined posture or seating that promotes hip abduction instead.
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Reclined
Reclined postures, where the chair back is at an angle of 100-110 degrees, can also be used to avoid fatigue
and discomfort. In this posture, the body is relaxed, the upper and lower back are well supported by the chair,
and back muscle activity and lumbar disc pressure are low.
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Upright
The upright posture places the operator's legs parallel to the floor with a thigh trunk angle of ninety degrees. Due to
muscle attachments on the pelvis, bringing the operator's thighs parallel to the floor results in the operator's pelvis
rolling backwards which causes the lumbar curve of the spine to flatten. Flattening the lumbar curve under these
conditions unequivocally causes the operator to slouch; it also increases the pressure on the intervetebral disks in the
lower back. Paraspinal muscles work against this to maintain the lumbar curve; however, they quickly fatigue under this
load, leaving most operators unable to comfortably maintain this posture for more than a few minutes at a time.
Whereas this posture is not unhealthy per se, operators should know its limitations and use the other postures to
avoid discomfort and slouching.
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Sources of DiscomfortThe following conditions will contribute to discomfort and should be
avoided.
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Slouching
When the muscles that hold the operator upright tire, they can no longer support the upper body.
The operator slouches forward, leaving the ligaments and joints to support the weight of the back. This strain
on the muscles, joints, and ligaments will lead to back pain. This also closes the angle of the body which can
increase pressure on internal organs. |
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Improper Fit
In order to properly use the declined posture with a forward-tilting task
chair, it is necessary to ensure that the seat-pan height range is sufficient to support the operator
in this position. Otherwise, this feature will only increase pressure on the tailbone, making the
chair less effective. This applies mainly to traditional task chairs. Please refer to the chair
selection guide or contact EHS for further information. |
Revised May 7, 2008
This information is made available to assist office workers at
Portland State University to maintain safe work practices with respect to office ergonomics.
It has been developed to be consistent with current standards, regulations, and research intending
to reduce risk factors of work related injuries at video display terminal (VDT) workstations.
This guide is not case specific and should be used as a suggestion only. For additional
information, contact Jason Mitchell at mitchelj@pdx.edu.
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