Article written by Gary Karp, Onsight Technology Education Services

The Ergonomics of Sitting

Having been doing training and evaluation for a couple of years now, certain patterns have clearly emerged. I'm convinced that ergonomics is still vastly ignored for its preventive prowess. Unfortunately this is especially true for folks who are symptomatic, even if they are getting treatment - more often not the case.

The most outstanding fact I've witnessed is that almost no one knows how to adjust their chair - even if they have the right one. No matter what you are sitting in, odds are it has some kind of adjustment, and there is potential for you to be better supported and more comfortable.

The whole point is to decrease static exertions in your body, and this is deeply related to how your chair carries you. Typical culprits are:

Seat pan angles tilted too far forward so your legs have to work to support you.

Seat backs set too low so the lumbar curve is left unsupported and the opportunity for thoracic support is lost (this is often the most dramatic moment of an eval - simply raising a back that is too low and the resulting instant sense of increased comfort).

Obstructions under the desk that prevent moving the chair close enough to be able to sit back in it and still reach the work tasks easily.

Chairs that tilt and won't lock in a fixed position, so the body has to work to stabilize itself, or always has to sit forward to prevent the tilt.

A very common Herman Miller chair that is still in a lot of offices is like this - always tilts. But there is a knob under it to tighten the spring tension, and I find many people who have it too loose. Most computer users do better with it tightened all the way.

Those with tilt locks should think of the chair as dynamic. Lock it for support while at the computer (using your arms, you want your body to be supported). But when someone comes in to chat or you are on the phone, that can be a good time to release the tilt and enjoying rocking a little. Be sure the spring tension is set for your weight. Too loose and you will feel like you might fall, too tight and you will have to exert force to rock. It should rock naturally just from the weight of your body.

Chair settings are not to fix and never change. If you learn what feels right and really know the controls, you will be able to choose options throughout the day depending on what you are doing. You'll be more comfortable, you won't be wasting muscular effort, and you won't fatigue so early in the day. That's the point.

And if someone who is going to share the chair changes it, don't complain. Consider that you want them to be safe, just as they should care about you. When everyone knows how to use the chair, it's no problem when each sets it for their needs.

Some chairs are just plain wrong for a given person. Seat pans are often too deep, especially in corporate "one-size-fits-all" settings. There is no way to sit against the back of the chair when this is the case unless you rotate the pelvis backward and round out the lower curve of the spine. In other words, you slump. Since the spine isn't able to do its strtuctural work anymore, that means that muscles have to do more work. Static work. That includes the neck and shoulders, which have to pull the head back to compensate for the slumped posture - especially if the monitor is too high. Now we have conditions that increase the chance of thoracic outlet problems, possibly impeding blood flow into the arms through the shoulders.

Certainly it leads to sore necks and shoulders. I find almost NO ONE who works at a computer who does not complain of this. They think it just goes with the territory, but there are real mechanical causes that can be easily addressed with ergonomics. At the same time, working too hard will always be a cause of pain and possibly disability.

I take away quite a few cushions that people use to adapt their chairs. Not because I don't believe in them, but because they typically have bought the wrong one. It is usually too thick, and very curved horizontally - a feature which is designed for lateral support, not usually the need. It may compensate for a deep seat pan, but it usually supports only the pelvis, and the rest of the back is robbed of support. Sometimes what's needed is a small cushion that can be fixed at a higher position to prevent the sense of "falling back" over the chair, many of which have too much angle in the back. The deep seat pan problem needs something serious like the Obus Forme product that costs $100. In general, cushioning is a budget-saving stopgap attempt that often can't solve the problem. For people who work long hours a the a computer, the right chair is worth every penny.

And they don't have to cost a thousand dollars. A company can get a good chair - or an appropriate variety to accommodate differences in size and need - for four or five hundred each if they just buy a few at once. Suppliers will deal. It seems to me that many managers never shop, and just live with the thousand dollar assumption.

So I have to wonder how many people who are experiencing RSI problems are focusing on all sorts of treatment measures, keyboards, voice dictation, and so on (I use these too) and missing the opportunities of good ergonomics. Any treatment is seriously compromised if the cause is not sufficiently removed. That includes the home too. What's happening in the kitchen?

It's not rocket science. It's common sense once you know the principles. So, all of you. Please make sure you know every control on your chair.

You are ALWAYS using muscles, so the level of risk is a matter of degree of continuous, low-level muscular contraction. The body is "designed" for movement, so sitting for long periods, no matter how "ergonomically correct" will become stressful in time. So what you are after is a repetoire of postures that you know to involve the least muscular effort in your body. It also means that when you slump and lean - which is comfortable just as a change and inevitable that we will do it in the course of a day - you are aware that it involves exertion, so you will limit the time you spend doing it. Don't be afraid of "bad" posture. Be afraid of letting such positions be the norm, or of your workstation ergonomics being such that you don't even have the option of supported posture.

In fact, sitting places more pressure on the spine and is not a neutral posture. It means you should stand up whenever you get the chance.

Here are a few "scientific" principles.

When the chin is dropped or raised, muscles have to work harder to support the head - no small task since it weighs on average about 15 pounds. This is why your monitor should not be too low.

If you never make contact with the chair back, your trunk works harder to balance you, which is why you will tend to slump back to make contact since it feels like a relief, even though it is "bad" posture. No back contact also means your trunk muscles work harder as you raise and use your arms. Think of the physics of what is going on as the loads increase when you lift your arms. This is why your keyboard should not be too high.

If your feet are not clearly in conctact with a firm surface, then either your legs become a load on the spine, or you will stretch your ankles and legs to make contact (or get into weird postures like putting your foot on a wastebasket). Better that you reach the floor. Footrests limit postural variety, so are best used as a last resort.

If the seat pan is tilted too far forward, you may feel you are sliding out of the chair, or just might not like the chair because it is adjusted wrong. Too much forward tilt also makes the legs do more work. At the same time, don't tilt too far back, because bringing the knees over thighs starts to rotate the pelvis back and round out the spine. That reduces its structural capacity, so muscles do more work.

Armrests that are too thin tend to require muscular efforts to keep the arms on them. Too hard and they can compress nerves, especially at the elbow. Too low and they encourage you to slump, though more often lean to one side. Too wide and you extend the arms out from the shoulders, too close and you do the same to avoid them as you work. Too high and they push up on the shoulders which push down in reaction (muscles always offer equal and opposite response, like Newton's law). Too long and they bump into things, stressing you out, or keep you from sitting back in the chair as you slide forward to get close to the work.

It is also a fact that the body gets trained into habitual postures, and adapts to them as "normal." Once you recognize what involves the least muscular exertion, you at first may need to make a point to sit that way until your body readapts. I used to be very curvey in my spine. What seemed very "wrong" at first is now the natural thing for my body, and good posture. This is why you need to take a couple of days (at least) with a new chair to let your body adjust. You can't know just by "trying it out."

I hear many stories of companies who get chairs to evaluate, but get no guidance in how to adjust them. It's no surprise when they say they don't like them. How could they know?


Other Ergonomics Articles by Gary Karp

Initial Thoughts on Cumulative Trauma Injuries
What is Ergonomics?
Computers and Cumulative Trauma
Why Are Cumulative Trauma Injuries Happening Now?
How Managers Can Reduce Cumulative Trauma
Myths Regarding Cumulative Trauma
Where Should the Keyboard Be?
Should You Use a Wrist Rest?
Keyboard Shortcuts in Microsoft Word
Wrist Braces and Cumulative Trauma

Sample Workstation Evaluation - "James"
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Last update: 10/11/99
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