At first we all simply plunked our computers on the desk we already had, a perfectly natural thing to do. There wasn't much cause to think about where the keyboard should go. Just start this thing up and let's fly!
It turns out that the location of the keyboard is a major force in our posture. Where our arms go, our bodies will follow. If we have to we will use our shoulder and trunk muscles to get our hands on those keys.
It's clear now that most of the desks we are using our too tall and force us in to all sorts of unnatural positions and static muscular effort. Even modular desk surfaces which can be easily lowered are left where they've always been. Here is what happens when the keyboard is too high.
Somehow the hands have to be brought up to a higher level to reach the keys. One answer could be to raise the shoulders up and spend all day doing Ed Sullivan impressions. This would be so noticeably stressful that we would not maintain this posture for long, though in fact we do this to a small degree anyway. It is one of the reasons that soreness in the shoulders and neck are so epidemic. Tall desk surfaces are a major cause.
Since we're unlikely to raise the shoulders enough we need to find other ways to compensate. One approach people use his to raise their chair up, usually taking their feet off the floor in the process. Not wanting to let their legs dangle off the end they will put their feet wherever they can for support. The supports of the chair become a typical perch for the feet, flexing the toes and ankles, bending the lower leg back at the knees, limiting circulation to the feet. Boxes and wastebaskets seem pretty popular, and I have seen walls covered with scuff marks. This "compensation" tends to promote slumped postures and usually lifts the legs off the pan of the chair leaving all of the weight of the upper body on the sit bones. Still worse, when it's time to move in the chair to another part of the office, the only way to push with the feet is to slump and stretch the legs, or else grab at the edges of the desk to pull themselves around.
Sometimes the raised chair approach just isn't possible. There are still a lot of old, metal office desks in use with a thick surface plus a drawer underneath that block the knees before the arms are up to the appropriate level.
The next compensation trick is to just push the keyboard farther away. If can't raise the arms up, then reach out in front of yourself. In this position the natural inclination is to lean forward on your arms, which will make your shoulders do some work anyway. By planting the arms on the desk, using the keyboard will involve a lot of bending the hand back and forth at the wrist because the arms are not free to move. You are also likely to also compensate by extending the elbows outward which increases the bend at the wrist and potentially puts pressure on nerves and tendons at the elbows.
If the desk is too narrow, pushing the keyboard farther away might mean the monitor has to move to the side, and now the head has to be kept turned to one side as you work. If the desk is deep enough then the monitor will still be pushed farther away and it will be necessary to lean forward - resting even more weight on the arms - in order to see the work.
Another common adaptation is to place the keyboard on the knees. For some, this does indeed accomplish the relaxed shoulders, open elbow angle, and straight wrists that are the goal of good ergonomics. For others, whose arms are shorter relative to the body, the wrists will tend to extend (bend backward) and/or to slump forward to compensate. For everyone, this means a fixed posture, since the keyboard must be balanced and pretty much kept in one position. There tends to be an extra level of tension in the whole body to make sure the keyboard doesn't fall off the knees. Since the body requires movement, this should be a temporary approach at best, generally only for those desperately horrible settings where the above concerns are least evils.
So, the simple fact of having the keyboard up too high brings with it all manner of efforts to compensate, most of which bring other problems with them. At the very least, these attempts to adjust won't stay comfortable very long.
Last update: 4/26/97
Copyright 1997, Onsight Technology Education Services