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BellaOnline's Ergonomics Editor


Computers and Ergonomics

Guest Author - virginia hixson

There are two main categories of issues that can result in computer related ergonomic injures: Posture and Repetition.


Repetition may seem obvious since the typing task is based on rapid repeated finger movement - however it is often NOT this finger motion that is the primary cause of problems. Not that the motion occurring at the finger level is unimportant – in fact without the repetitive finger action injury would be far less frequent. With perfect technique, even with the repetition, injury would seldom occur. Most of the other ergonomic risk factors are minimal.

More often repetition based injuries have to do with the angle of work, often with the wrist or thumb. Carpal Tunnel and other flexor tendonitis? WRIST! De Quervain’s? THUMB and/or WRIST! Extensor Tendonitis? WRIST! Ulnar tendonitis? WRIST!

Even repetitive injuries have a lot to do with joint and limb and total posture. No part of the body acts alone. When one part moves, another is affected. This is especially true of muscles that traverse the same joints. When flexors contract, in order to allow easy movement, the extensors relax. Muscle control for fine movement (needed for typing) is achieved by a very fine coordination between flexors and extensors.


You can achieve a very low stress posture by just aligning your spine and relaxing. Let your arms fall to your lap, your elbows, wrists and hands relax. Most probably, you have ended up in the position ergonomists call neutral. Elbows are slightly flexed, wrists are essentially straight, the hand rests with the thumb facing up and the fingers slightly curled.

In this position, your wrists and hands are almost at their strongest. Strength is increased by bending the elbows to 90 degrees and stabilizing arms against the side of your body.

This demonstrates a basic principle – for stability and strength, limit mobility - but the opposite is also true. In order to get mobility, you need to limit stability.

Researchers in the fields of biomechanics and ergonomics have found that holding one position (static contraction) can also be a risk. In order to maintain a sable unsupported position, both the flexors and extensors must be constantly working against each other. Better for health is a work/relax cycle. So, another principle is ‘the best position is the next position’.


Computers are amazing tools. They increase our capacity to work and store knowledge to an unbelievable extent... AND they are engrossing. It is very difficult to maintain body awareness if you are focused on your work. If you are a touch typist, which most of us are these days, typing is automatic. You think the thoughts and they appear on the screen. How do you remember that your wrists should be straight, or that you shouldn’t hold your fingers up in the air over the mouse while you move to the next button you need to click?

Practice, Practice, Practice.

Choose routine tasks that don’t have close deadlines for your practice. You don’t want to try practicing on something that takes a lot of attention. You want to keep your attention on how loose and active your hands and wrists and elbows can be. There should be low force, fluid motion beginning at the shoulder and extending down through the elbow, wrist, and finally the fingers, which do a little light dance across the keyboard. Your motion should include some forearm rotation, perhaps a little trunk movement or weight shifting.

The main thing is mobility, not stability. Strength is not called for – and keys are really very large targets for our fingers. If you get off by a key or row, your eyes immediately (or almost immediately) catch the error.

This technique was developed by Dr. Norm Kahan in Cupertino, and Vivienne Fleischer in Oakland. I’ve provided links to their websites at the bottom of this article. For more information, tools, and training, contact either one of them.

I have found it very helpful both personally and with several of my clients.

Positions to Avoid

Wrist angles of more than 15 degrees toward the thumb or little finger
Wrist angles of more than 15 degrees up or down
Pinch grips
Fingers held extended in the air (usually over the mouse, sometimes over specific keys – or when resting the palm on the desk or wrist rest.
Elbows closed tighter than 90 degrees

For discussion of other issues, see articles on seating (most computer works spend most of their computer time seated) and posture.

Norm Kahan: http://www.mousekeydo.com/
Vivienne Fleischer: http://www.linksv.com/compSummary/sp/59173/PerformanceBasedErgonomics

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Content copyright © 2015 by virginia hixson. All rights reserved.
This content was written by virginia hixson. If you wish to use this content in any manner, you need written permission. Contact BellaOnline Administration for details.


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