Desks for Comfortable Computer Use
Monitor, Keyboard and Mouse Must Be Positioned for User's Health
Correct design means ergonomic design; i.e., dedicated to the healthy interaction of a person to his or her environment, particularly machinery and furniture.
Display Position
Ergonomically, the height of a computer monitor should allow the user to keep the head straight and not tilt up or down, which can strain the neck. Eye level should be 2 to 3 inches (5 to 7.5 cm) below the top of the monitor casing. Cornell University’s Human Factors and Ergonomics Research Group advises that when a person holds an arm out horizontally, the fingertips should touch the center of the screen. (See point 2 on the attached diagram from Cornell.)
This arm reach also places the screen at the best distance (point 4).
Display holders for flat screens are easier to adjust than holders for bulky CRT displays.
Screen height can be a problem for people who wear trifocal or progressive-lens glasses. Cornell suggests they recline in the chair and avoid sitting upright (1 in the diagram). Some ophthalmologists prescribe ‘working’ bifocals for computer use.
Documents should also be placed where they cause little movement of the head:
- Between the screen and keyboard (6);
- To one side at screen height on a document holder attached to the display; or
- On a holder standing beside the monitor and angled slightly towards the user.
Keyboard and Mouse
The keyboard tray should be about 3/4 to 1 1/4 inch (2 to 3 cm) below elbow height so the user can type with forearms at an angle greater than 90 degrees to the upper arms (7, 8). This helps to prevent compression of nerves at the elbows.
The tray should slide or swivel out for the person to use the keyboard without having to reach, so that upper arms are upright and relaxed at the side of the body. This avoids strain on shoulder muscles.
To keep the wrists straight in line with the forearms, the tray should be tilted (10) so the back is lower than the front (a negative tilt). Flexure of the wrists can cause inflammation of the nerves to the hand (carpal tunnel syndrome).
Low-cost keyboard trays can be attached under a desk surface so they pull out on drawer glides. A tray on an articulating arm is better since it can be set for tilt and height.
The keyboard should center the letter keys, not including the pad of number keys to the right of a full-size keyboard, in front of the user (9).
The mouse should also be positioned so it can be used with arm and shoulder relaxed, without reaching. Research at Cornell has shown the best position for a mouse for right-handed people is over the number pad. Some keyboard holders have mouse trays that can be swiveled over the number keys. In another type, the tray slides to left or right.
Healthy Posture
Also in the Cornell diagram: 3 refers to avoiding glare on the screen; 5, chair height should place feet flat on floor or a foot rest; 11, worksurface and keyboard tray should be stable (no bounce); 12, Cornell advises people to take frequent short breaks.
The space under the desk must be free of obstructions to feet such as trash cans, boxes and files, which can cause a person to move the chair away from the desk and lean forward, defeating the purpose of ergonomic design.
For anyone using a computer frequently for more than one hour at a stretch, the positioning of monitor, keyboard, mouse and documents makes the difference between comfort and the pain that comes from strained muscles and joints.
Other source: Association of Canadian Ergonomists
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