Sarasota PC Monitor
Ergonomic Tips (11/00)
Ergonomic chairs and adjustability options
by John R. Chait D.C., drchait@home.com
Member of the Sarasota Personal Computer Users Group, Inc.The features described here allow a chair to adjust to a given posture or body size, but it is important to remember the importance of posture change. Adjustability features should allow freedom of motion in the spine.
Seat height
The user is able to adjust the chair so that their feet are on the floor, or the work surface or keyboard is at an appropriate height, or preferably both.
Seat depth
Achieved either by backrest in-out adjustability or by a sliding seat pan, this changes the front-to-back depth of the seat. A shorter seat pan is necessary to allow smaller people to use the chair's backrest, while a deeper one feels more stable to taller individuals.
Backrest angle
This refers to changing the angle of the backrest relative to the angle of the seat. This can be achieved with an adjustment mechanism or through the use of bending materials or springs in the chair shell.
Backrest angle
This allows the chair to support different degrees of recline, which in turn transfers some upper-body weight to the chair backrest and lightens the load on the lower back.
Backrest angle
This also increases the angle between the torso and the thighs, which causes the lower back to curve inward. This inward curve, called "lordosis," results in less pressure on the discs than a flat spinal shape.
Chair recline, or tilt
This changes the angle of the entire seat relative to the floor. As with backrest angle adjustability, a reclined chair transfers some upper-body weight to the backrest of the chair.
Seat pan angle
This generally refers to changing the forward-back angle of the seat. It consists of a choice of fixed angle, rather than a free-floating recline. Often, this feature provides forward tilt, in which the thighs slope downward. The main purpose of forward tilt is to open the angle between the trunk and thighs, inducing a lordotic curve into the spine and reducing pressure on the discs.
Armrests
These support the arms, reducing the work of the shoulders and possibly the upper arms. Armrests can, however, be used inappropriately by inhibiting free motion of the arms during activities such as typing.
Height-adjustable armrests
These help avoid the problems of too-high armrests, which result in elevated shoulders and pressure on the undersides of the elbows and forearms, and too-low armrests, which require the worker to slump or lean to one side to use them.
Width-adjustable armrests
This kind of adjustability changes the distance between armrests. Armrests that are close to the body can help avoid splayed elbows, which in turn cause the wrists to bend to the side during activities such as keying.
Padded armrests
These potentially avoid uncomfortable pressure on the undersides of the forearms and elbows.
Lumbar support
This is intended to prevent, to the extent possible, the flattening of the lumbar spine that occurs in most people when seated. Lumbar support is usually done through gentle curves in the backrest shape. In this state the spine is much more resilient.
Backrest height adjustability
This refers to a change in height of the lumbar support area of the chair backrest, although this feature is often interpreted to mean a change in height of the entire backrest. This feature accommodates preferences by different workers regarding where and how the lumbar support curve contacts the back.
Lumbar depth adjustability
This affects the size and sometimes the firmness of the lumbar support curve in a chair's backrest. Like backrest height adjustability, it accommodates different preferences and body shapes. :
_______________________________________________________________ Copyright 2000. This article is from the November 2000 issue of the Sarasota PC Monitor, the official monthly publication of the Sarasota Personal Computer Users Group, Inc., P.O. Box 15889, Sarasota, FL 34277-1889. Permission to reprint is granted only to other non-profit computer user groups, provided proper credit is given to the author and our publication. We would appreciate receiving a copy of the publication the reprint appears in, please send to above address, Attn: Editor. For further information about our group, email: admin@spcug.org/ Web: http://www.spcug.org/
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