Modern office chairs are generally quite good as long as you are not among the 10 % smallest or biggest size range in any body demension, and as long as you have no special physical needs.
Most chairs have individual adjustments for any chair demension. If the range of adjustment is not large enough, you can generally special order parts. For me, my arm is long enough in proportion to my body that I generally have to order a shorter arm height for my chairs.
Here are some basic definitions of the chair adjustments you should explore. Keep in mind that chair deminsions are usually comparing one part of the chair to another — so that arm height is NOT height from the ground, but height above the seat pan.
This article is focused on the seat pan, the actual part of the chair you sit on.
- Chair Height
- Chair Height is measured from the floor to the top of the seat pan when it is adjusted to a flat position. Standard chair height is 19 inches. Seat height should be easily adjustable so that it can change during the day as your work tasks change.
Seat height can be adjusted in relation to the floor if your work surface is height adjustable. If not, you will need to measure in relationship to the work surface and have a footrest handy. Yourfeet should be weight bearing on the floor or on a footrest. There should be minimal pressure at the back of your knees. (To identify appropriate work height, please see an article on work height).
- Seat Pan
- The Sean Pan is the part of the chair you actually sit on. It is measured in both its width (distance between chair arms) and depth (front to back).
- Depth of Seat Pan
- The depth of the Seat Pan is important because if it is too deep, poor sitting posture and excessiven tension in the back, shoulders and neck are often the result. The back cannot gain the support it requires from the chair back because the person cannot physically reach it while maintaining good posture without compromising leg and knee positions. The chair is just too long for the legs. Many newer chairs have seat pan sliders allow you to change the depth within a limited range.
If the depth is too shallow, the legs do not get the support they need and the person constantly exerts force in order to remain balanced in the chair. Either condition can result in perching on the edge of the chair. While this is not an issue for a short time, it becomes one if maintained for several hours.
- Seat Pan Tilt
- Seat Pan Tilt describes the angle of the seat pan to the floor. If the seat pan is in a forward tilt, the front is angling downward, pointing toward the floor. If the seat pan is in backward tilt, the front of the seat pan is angling up and the back is pointing downward toward the floor.
These tilts are used to achieve different postures required by different work set-ups and different tasks.
Forward TiltThe chair in forward tilt is used when reaching around and above the desk top is required. This might be for tasks such as answering the phone, writing notes in long-hand, collating, stapling, etc. The forward tilt brings the shoulders higher and brings the arms in a better position for reaching.
Forward Tilt is generally better for increasing blood flow in the legs, but does not work well if the person wears silky fabrics on the lower body - especially layered. The person will feel like they are falling out of the chair and will not be able to get comfortable. It is better to start with a flat seat pan and gradually increase the tilt angle.
Backward TiltThe seat in backward tilt unweights the spine and allows better relaxation of back and shoulder muscles (unless you are trying to reach forward).
In backward tilt beyond 15 % neck support should be provided to prevent neck strain. Backward tilt to 15 % is frequently a good choice for a worker who is an executive (talking, thinking, reading and reviewing light weight material), or who can bring the worksurface close to him or her by use of a keyboard platform (in jobs with little reaching), or a drawing board. CAD designers often prefer this set-up and it frequently is appropriate. This type of seating is also appropriate for 911 operators or plant engineers who must moitor displays that are set above the optimum viewing height.
There are several more chair options and measurements to be concerned with and these will be discussed at a later date.
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