The magazine of the Melbourne PC User Group
Ergo-Solutions
Mary Levens
 maryl@melbpc.org.au

No, this is not a software review! An April BBS message recommended an aid for computer users suffering back pain. I realised that I had not noticed any treatment of work-station design in PC Update. Prevention is better than a cure and, even for those who already have pain, knowledge about how to set-up space for computer use would be useful.

An ergonomic workstation can be set up with little effort or great expense using today's fully adjustable seats, desks, monitor supports, footrests, and document holders. With this gear you can ensure that all users in your household have a safe work-station. For those of us who have an old door sup-ported on packing cases which passes as a desk, and front up to this sitting on an old kitchen chair, life was not meant to be full of aches. Now is the time to do something about your workstation.

Computer workstation ergonomic design should positively encourage optimum posture and minimise eye fatigue, so the user can play or work in comfort and safety. This article will guide you to the ergonomic "ideal" and to the rules of thumb which make the setting-up easier, whatever your decor. There is no intention to advise with respect to characteristics of ergonomic "best" equipment.

Your Posture

Try this exercise. Stand erect with feet comfortably apart and parallel, arms hanging loosely by your sides. Relax without slouching. Now, except for a few missing right-angles, this is a good posture for seated work. While still standing, get a feeling for the position of your body:
  • Trunk and head are erect with neck neither flexed nor extended
  • Upper arms hang loosely with elbows by sides
  • Forearms and hands are in line and fingers are slightly curved (this is called the position of function)
  • Feet are flat on the floor and at right angles to the lower legs.
Try to maintain the relative position of the parts within each of these body regions when you sit at a computer. 

Sit as near to the desk as possible with trunk and head erect, and the small of the back supported by a seat backrest. 

Seat and Desk Height

Seat and desk height should allow minimal clearance between top of thighs and underside of desk to ensure that:

  • forearms are horizontal
  • hands are in the position of function
  • upper arms and elbows are hanging loosely at your sides
A good guide is to rest your hands flat on your thighs and have the underside of the desktop just clear your knuckles. There may be problems with this height adjustment if the thickness of the desk top exceeds 30 mm. (Note that for clerical work the rule of thumb is that the underside of the desk top should just clear two clenched fists one on top of the other, thumbs uppermost, on the thigh).

Elbows should be free to move and not jammed between your ribs and chair armrests. Remove arm rests which hinder arm position.

Use a foot rest, such as recycled telephone books. Your lower legs need not be vertical as in the standing position, however, you should ensure that:

  • feet are supported at right angles to the lower legs
  • thighs are horizontal
Horizontal thigh-position minimises pressure on the underside of the thighs which may interfere with circulation. If you have enough leg-room under the desk use it to waggle your legs occasionally.

The arc swept out by your forearm and hand, with upper arms still by your sides, should allow you to reach frequently used items such as the keyboard and mouse. Less often required items should be within reach of fully extended arms without the need to move your torso far from its erect position. Stand to reach anything else.

The Keyboard

Keep the keyboard as flat as possible. Home-row keys should not be more than 30 mm in height from the top of the desk. Fold up those little legs on the rear underside of the keyboard.

Push the keyboard in from the edge of the desk to allow a smooth surface on which to rest the base of your hand when not typing. The distance from the keyboard to the edge of the desk will depend on the length of your forearms. The keyboard position should allow you to comfortably maintain the position of your upper arms by your sides.

The Monitor

Clean the screen. Position your monitor to ensure the screen is free from glare and reflection. Cross lighting is preferable. Avoid major light sources positioned behind the monitor or behind the user.

Adjust monitor height so the viewing angle is approximately 20 degrees from the horizontal line of sight to the screen centre line. A good rule of thumb is that the top of the monitor should not be higher than the horizontal line of sight.

Adjust your monitor display to ensure that:
  • minimum character size is 3-4 mm
  • colour uses dark characters on pale background
  • minimum contrast is 3:1
The typical viewing distance is 450-600 mm. As a guide, the viewing distance should not exceed character height x 150. This distance will be marginally greater than the distance from the front edge of the desk to the screen. Narrow desktops pose a problem for this adjustment.

Position hard-copy documents as near as possible to the screen with viewing angle and distance similar to that of the screen.

Eye movement and left-right head movement should enable you to see everything you need to without bending the neck. The ability to touch-type is of great benefit here.

Now try working in that position. I'm off for a massage!

Reprinted from the June 1993 issue of PC Update, the magazine of Melbourne PC User Group, Australia
 

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