Thought Bytes...
September 2002

Choosing a Chair - Part 1

There are sooooo many chairs to choose from. What features should you look for? What price should you expect? What kind of terms of sale are reasonable?

First of all, the chair you choose for working at the computer is intended to encourage the best possible seated posture. This is particularly important if you are a dedicated computer user – one who sits at the computer for a cumulative of several hours each day. The goal correct seated posture is:

• Feet supported
• Ankles forward of the knee
• Three finger gap behind the knee
• Thighs parallel to the ground or slightly angled down
• Lower back supported by the lumbar curve of the chair
• Leaning back so that the upper body is also supported by the chair.

This position will reduce strain to the postural muscles by allowing them to relax periodically. This will encourage blood flow to the muscles which will provide oxygen and remove the by-products of metabolism.

There are two types of "ergonomic" chairs which can help facilitate proper seated posture. An active ergonomic chair is one which is virtually fully adjustable. But it doesn't have to be so high-tech that you need an engineering degree to be able to operate it. In fact, the simpler the adjustments, the more likely a person is to use them. The most important features of this chair are (in order of priority):

1. Adjustable seat height
2. Lumbar support which curves to fit the natural curve of the spine
3. Adjustable seat back height and angle
4. Adjustable depth for seat
5. Easily accessible levers, knobs or buttons
6. Curved front edge to reduce pressure on the backs of the legs
7. Adjustable angle for seat
8. Woven, breathable fabric
9. Optional/removable arm rests
10. Adjustable height and width arm rests

Lets look at each of those features in a bit more detail:

Adjustable seat height
Most chairs come with a pneumatic seat height adjustment, or at least have it as an option. This allows you to set the chair height according to the stature of the person using it.

Lumbar support which curves to fit the natural curve of the spine
When you go to a show room (which implies that I do not encourage people to buy chairs from catalogues), run your hand down the middle of the backrest of the chair. You should feel a distinct lump protruding that will fit into the lumbar curve of your back. Don’t be satisfied by seeing a curve from the side of the chair - looks can be very deceiving.

Adjustable seat back height and angle (and tension)
Chairs that do not have adjustable height backrests are designed to fit one body - typically a leaner, more muscular body than most office workers. People with extra buttock tissue are effectively sitting on a pillow. This raises them up causing the lumbar support of a fixed backrest chair to place pressure on the sacro-iliac joints. This can lead to SI irritation and pain. In some cases, it can be a contributing factor to sciatic nerve irritation. The backrest should adjust so that the lumbar support fits into your lumbar curve. That’s the curve that you have when standing, that flattens when you sit. The backrest should support the back when you are leaning back. People with more upper body weight will need to tighten the tension on the backrest so that it does not flop away from them. In some cases, it will be necessary to lock the backrest so that it is firmly supportive. I usually prefer to see some movement in the backrest so that postural muscles are not holding a fixed position for hours on end.

Adjustable depth for seat
Depth adjustment for the seat of the chair is becoming more common. The seat of the chair should support the thigh up to about a three finger gap behind the knee. We naturally sit in a position that protects the nerves and blood vessels at the back of the knee. If the seat pan is too long, most people will just sit forward – meaning that they have no back support. In this case you might need to add a pillow or piece of foam to fill in the gap. If the seat pan is too short, and not enough thigh is supported, you will feel like you are falling out of the chair. In this situation, there is a tendency to brace the feet, creating tension throughout the body.

Easily accessible levers, knobs or buttons
Ergonomic chairs should be easily adjustable from a seated position. In some less well designed chairs, it may be easier to have someone help to adjust the backrest of the chair. That way you can set the lumbar height without significantly reaching down to tighten the knob.

Curved front edge to reduce pressure on the backs of the legs
The seat pan of the chair should have minimal contouring, except at the front edge where it curves like a rock smoothed by eons of water flowing over it (which is why it is called a waterfall edge). Seats that have a lot of contouring will fit fewer people. Those with more generous thighs will find contouring uncomfortable.

Adjustable angle for seat
Most people can leave the seat pan in a horizontal position. Because our thighs are wedge shaped, sitting on a flat surface still creates a bit of angle to the surface of the legs. An extreme angle (particularly when combined with slippery clothing) will make you feel like you are sliding out of the chair.

Woven, breathable fabric
Personally, I don’t like leather on an office chair. Sure, it looks very posh, but my skin gets over heated!.

Adjustable height and width arm rests
Arm rests can be more of a hindrance than a help, to be quite frank. We have gotten by for the last 20,000 years without arm rests and have all the structures that we need to hold the arms in a relaxed position against the sides of the body. If the arm rests of the chair are not adjustable to fall under the elbow in a relaxed arm position, they will encourage reaching to the side (resulting in ulnar deviation of the wrists), hunching the upper back (and extension of the neck), slouching in the chair and leaning to the side. If you have to move your elbow away from your body in the slightest - remove your arm rests!

Pricing

Prices for "ergonomic" chairs vary from approximately $250 to over $1500. Sometimes more expensive is not necessarily better. But, when it comes to fit and quality, you usually get what you pay for. Consider "investing" in your chair. If you buy a cheap chair that has to be replaced every 3 years and is not comfortable – likely, you will not be as productive as if you have a chair that is well suited to your stature, tasks and physical needs.

Terms of Sale

Sitting in a chair in the showroom for 5 minutes is not enough time to determine if a chair is going to fit you and work in your environment. Any chair that you purchase should be fully returnable (in good working order) after a 10 day trial. Most companies that I deal with allow a 1-2 week trial period.

Don’t get roped into a situation where you can only return the chair and select another chair from their product line (i.e. some big box stores) because most of their chairs are made by the same manufacturer. What bugged you about the chair you are returning will likely be present in the next chair.

Next month

I have to admit that I ran out of time this month to survey some of the chair suppliers / representatives on their favourite chairs for different body types. So, in the October issue, look forward to their picks (with my commentary) for chairs for small, tall, skinny, wide and average bodies.

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