As we noted above, the keyboard should be as thin as possible. It is usually recommended that its slope should be adjustable, although in biomechanical terms a very slight rake would seem preferable to a steeper one.
Users often have strong views about the ‘feel’ of different keyboards. One user once described the difference between working at two particular makes of keyboard as ‘like the difference between walking on turf and walking on pavement’. At present,
Figure 6.3 The laptop computer. Note the posture of the neck.
however, we know little or nothing about these matters on a formal scientific basis.
The features of the keying action, which give the keyboard a ‘good feel’, remain elusive. Different users seem to have different (and sometimes conflicting) views on the subject.
There is good evidence that neither the conventional QWERTY keyboard layout, nor the presentation of the alphabetical keys in a single rectangular key field on a plane surface, is an optimal ergonomic solution to the problem of keyboard design (see Pheasant 1991a,b, for a detailed discussion). The former issue is to all intents and purposes a lost cause. There may be more realistic opportunities for improvement in terms of the latter. The basic problem with the plane keyboard and rectangular key field is that a degree of ulnar deviation will inevitably be required to maintain the alignment of the fingers at the keys. (This is accentuated if the keyboard is too high, see above; and if the user leans forward, see below). A number of ‘split keyboard’
designs have been proposed to overcome this problem. Initial trials of these seem encouraging (see, e.g., Grandjean 1987), but as yet they show little or no sign of catching on.
6.4.1 Other input devices
We may confidently predict that as time goes by the keyboard as such will increasingly be replaced by other devices for entering information onto the machine and otherwise controlling its functions. The extent to which these will supplant the keyboard in everyday applications—or perhaps more realistically the rate at which they will do so—is impossible to estimate at present.
The most widely used input device other than the keyboard at the present time is the ‘mouse’. There are already signs that people who use the mouse extensively (in layout work, etc.) are prone to suffer from upper limb disorders similar to those of keyboard users—the causative factors presumably being the particular combinations of static muscle loading due to working posture and the repetitive motions of the wrist and/or fingers that the tasks in question entail.
The ultimate alternative to the keyboard (short of psychokinesis) is voice input. It will doubtless be found to cause RSI of the vocal chords.
6.5 ‘Good posture’ in screen-based work
Concern over the increased reporting of work-related upper limb disorders in the white-collar population (see Section 8.5) has led to an increasing demand that keyboard users should be taught ‘the correct way to sit’. To the layperson this requirement may seem straightforward enough. It is not quite as simple as it seems, however, and a number of unresolved issues remain. There are two basic schools of thought concerning the matter. We could call these the orthodox or ‘perpendicular’
approach, and the alternative or ‘laid-back’ approach. The postures in question are illustrated in Figure 6.4. The views that people take on these matters are not always stated entirely explicitly—and indeed the whole issue is surrounded by something of an air of vagueness. Overall, the adherents of both schools would be in a broad measure of agreement concerning the anthropometric criteria proposed at the beginning of this chapter. They would also agree that working postures that entail
forward leaning (and in particular the yuppie hump) are highly undesirable. The principal points at issue are, first, the desirable position of the trunk, and second, whether or not the wrists should be supported.
The perpendicular position for keyboard work (in which the trunk is as far as possible kept upright with the back principally supported in the lumbar region so as to maintain its ‘normal’ curve) has, to this author’s knowledge, been taught in schools of typing since the 1930s at least. It may be regarded as representing the
‘conventional wisdom’ on the subject, which until the mid-1980s or thereabouts would have commanded more or less universal consent. People who still teach the perpendicular position sometimes refer to it as ‘sitting in balance’. This sounds very good. But it does not really get us much further forward in understanding the issues involved, in the absence of a formal explanation of what is meant by ‘balance’, framed in the language of physiology and biomechanics. Such an explanation, in this author’s experience, has not been forthcoming.
The first significant challenge to the orthodox view was made by the late Professor Etienne Grandjean and his co-workers in Zurich, in a series of papers published in the early 1980s, the findings of which are summarized in his book The Ergonomics of Computerized Offices (1987). Grandjean’s views were based upon trials in which VDU users were provided with fully adjustable chairs and workstations to use in their own offices. The great majority of subjects preferred a ‘laid-back’ position in which the trunk was reclined by between 10° and 20° to the vertical. (Only about 10% of subjects chose to sit upright.) Where a padded wrist support was available, the great majority of subjects (80%) chose to use it; and where it was not available around half of the subjects chose to rest their wrists on the desk. On average the subject’s elbows were flexed to a little less than a right angle, so the forearms were inclined slightly upwards.
Grandjean (1987) argues forcefully that in biomechanical terms there is nothing whatsoever wrong with this position. He mainly bases his views on the experimental evidence of Anderson et al. (1974, cited in section 4.2 above) who showed that when
Figure 6.4 Working posture at the visual display terminal as recommended by Cakir et al. (1980) (left) and Grandjean et al. (1987, 1984) (right).
the trunk is so reclined, the loading on the lumbar spine is substantially less than it is when sitting upright. He does not, however, explicitly address the issue of upper limb disorders in this context.
On balance, a supported wrist when using the keyboard would seem to be desirable rather than otherwise, in that it will reduce the static loading on the muscles of the neck, shoulder and arm. There are two caveats to this general position. One is that supporting the wrist on the sharp edge of the desk (which you see quite commonly) can cause blunt trauma to the tissues of the front of the wrist (and in particular the ulnar nerve). The second is that it may result in a ‘cocked’ (i.e. extended) wrist, which results in a static loading of the muscles in the extensor compartment (i.e.
back) of the forearm. The latter is particularly likely to be a problem if the keyboard is abnormally thick or if it is used in a steeply raked position. Both are highly undesirable. Both may be avoided by the use of a padded wrist support.
In addition to reducing the mechanical loading on the lumbar spine, the laid-back sitting position (particularly when combined with the supported wrist) has the additional advantage of tending to increase the overall horizontal distance between the user’s shoulders and the keyboard. (The disadvantage that would accrue in terms of static load is eliminated by the supported wrist.) It follows, as a matter of geometry, that the degree of wrist deviation required to maintain the alignment of the fingers on the keys will be correspondingly diminished. As the trunk moves from a reclined position to an upright position, and then from an upright position to a forward sitting position, the elbows must also move out sideways to accommodate the width of the lower part of the rib cage. This results in a further and progressively more pronounced ulnar deviation of the wrist.
Figure 6.5 Keyboard worker in a natural, relaxed position.
Opponents of the laid-back approach argue that it tends to degenerate into a slumped position similar to that of the yuppie hump. By the same token, the upright position will tend to degenerate into a forward slump. With a well-designed seat that gives good back support, the former tendency will in my view be minimal; whereas the latter will still be present to a more marked extent, particularly when the user is tired or under stress.
On the basis of these various considerations therefore (and notwithstanding my comments on the subject in earlier writings), I am currently of the opinion that the laid-back position for keyboard work offers material advantages as compared with the perpendicular position. Having said this, I remain disinclined to be unduly prescriptive in advising the individual keyboard user as to what constitutes a ‘good posture’. It is more important that he or she should learn the importance of postural diversity in the workplace and the avoidance of unnecessary muscle tension. The laid- back position is only desirable in that it is materially more likely to achieve these aims.
Figure 6.5 (which was taken from an unposed original) shows a keyboard worker in a natural relaxed sitting position at a well-designed fully adjustable workstation.