The status of ageing workers varies according to their functional condition, which itself is influenced by their past working history. Their status also depends on the work post that they occupy, and the social, cultural and economic situation of the country in which they live.

Thus, workers who have to perform much physical labour are also, most often, those who have had the least schooling and the least occupational training. They are subject to exhausting work conditions, which can cause disease, and they are exposed to the risk of accidents. In this context, their physical capacity is very likely to decline towards the end of their active life, a fact that makes them more vulnerable at work.

Conversely, workers who have had the advantage of lengthy schooling, followed by occupational training that equips them for their work, in general practise trades where they can put to use the knowledge thus acquired and progressively widen their experience. Often they do not work in the most harmful occupational environments and their skills are recognized and valued as they grow older.

During a period of economic expansion and shortage of labour, ageing workers are recognized as having the qualities of “occupational conscientiousness”, being regular in their work, and being able to keep up their know-how. In a period of recession and unemployment, there will be greater emphasis on the fact that their work performance falls short of that of younger people and on their lower capacity to adapt to changes in work techniques and organization.

Depending on the countries concerned, their cultural traditions and their mode and level of economic development, consideration for ageing workers and solidarity with them will be more or less evident, and their protection will be more or less assured.

The time dimensions of the age/work relationship

The relationship between ageing and work covers a great diversity of situations, which can be considered from two points of view: on the one hand, work appears to be a transformation factor for the worker throughout his or her active life, the transformations being either negative (e.g., wear and tear, decline in skills, illnesses and accidents) or positive (e.g., acquisition of knowledge and experience); on the other hand, work reveals the changes connected with age, and this results in marginalization and even exclusion from the production system for older workers exposed to demands at work that are too great for their declining capacity, or on the contrary allows for progress in their working career if the content of the work is such that a high value is placed on experience.

Advancing age therefore plays the role of a “vector” on which events in life are registered chronologically, both at and outside work. Around this axis are hinged processes of decline and building, which are very variable from one worker to another. In order to take into account the problems of ageing workers in the design of work situations, it is necessary to take into account both the dynamic characteristics of changes connected with age and the variability of these changes among individuals.

The age/work relationship can be considered in the light of a threefold evolution:

1. Work evolves. Techniques change; mechanization, automation, computerization and methods of information transfer, among other factors, tend or will tend to become more generalized. New products make their appearance, others disappear. New risks are revealed or extended (e.g., radiation and chemical products), others become less prominent. Work organization, labour management, the distribution of tasks and the work schedules are transformed. Some production sectors develop, while others decline. From one generation to another, the work situations encountered during the active life of the worker, the demands that they make and the skills that they require are not the same.
2. Working populations change. Age structures are modified in accordance with demographic changes, the means of entering or retiring from work and attitudes towards employment. Women’s share in the working population continues to evolve. Genuine upheavals are occurring in the field of education, occupational training and access to the health system. All these transformations are at the same time producing generation-related and period-related effects which obviously influence the age/work relationship and which can to a certain extent be anticipated.
3. Finally—a point that deserves emphasis—individual changes are in progress throughout one’s working life, and the adjustment between the characteristics of particular work and those of the people who carry it out is therefore frequently called into question.

Some processes of organic ageing and their relationship to work

The main organic functions involved in work decline in an observable way from the ages of 40 or 50, after some of them have undergone development up to the ages of 20 or 25.

In particular, a decline with age is observed in maximum muscular strength and range of joint movement. The reduction in strength is in the order of 15 to 20% between the ages of 20 and 60. But this is only an overall trend, and the variability among individuals is considerable. Moreover, these are maximum capacities; the decline is much less for more moderate physical demands.

One function that is very sensitive to age is regulation of posture. This difficulty is not very apparent for common and stable working positions (standing or sitting) but it becomes obvious in situations of disequilibrium that require precise adjustments, strong muscular contraction or joint movements at extreme angles. These problems become more severe when the work has to be carried out on unstable or slippery supports, or when the worker suffers a shock or unexpected jolt. The result is that accidents due to loss of balance become more frequent with age.

Sleep regulation becomes less reliable from the ages of 40 to 45 onwards. It is more sensitive to changes in working schedules (such as night work or shift work) and to disturbing environments (e.g., noise or lighting). Changes in the length and quality of sleep follow.

Thermoregulation also becomes more difficult with age, and this causes older workers to have specific problems with regard to work in heat, particularly when physically intense work has to be carried out.

Sensory functions begin to be affected very early, but the resulting deficiencies are rarely marked before the ages of 40 to 45. Visual function as a whole is affected: there is a reduction in the amplitude of accommodation (which can be corrected with appropriate lenses), and also in the peripheral visual field, perception of depth, resistance to glare and light transmission through the crystalline lens. The resulting inconvenience is noticeable only in particular conditions: in poor lighting, near sources of glare, with objects or texts of very small size or badly presented, and so on.

The decline in auditory function affects the hearing threshold for high frequencies (high-pitched sounds), but it reveals itself particularly as difficulty in discriminating sound signals in a noisy environment. Thus, the intelligibility of the spoken word becomes more difficult in the presence of ambient noise or strong reverberation.

The other sensory functions are, in general, little affected at this time of life.

It can be seen that, in a general way, organic decline with age is noticeable particularly in extreme situations, which should in any case be modified to avoid difficulties even for young workers. Moreover, ageing workers can compensate for their deficiencies by means of particular strategies, often acquired with experience, when the work conditions and organization permit: the use of additional supports for unbalanced postures, lifting and carrying loads in such a way as to reduce extreme effort, organizing visual scanning so as to pinpoint useful information, among other means.

Cognitive ageing: slowing down and learning

As regards cognitive functions, the first thing to note is that work activity brings into play basic mechanisms for receiving and processing information on the one hand, and on the other, knowledge acquired throughout life. This knowledge concerns mainly the meaning of objects, signals, words and situations (“declarative” knowledge), and ways of doing things (“procedural” knowledge).

Short-term memory allows us to retain, for some dozens of seconds or for some minutes, useful information that has been detected. Processing of this information is carried out by comparing it with knowledge that has been memorized on a permanent basis. Ageing acts on these mechanisms in various ways: (1) by virtue of experience, it enriches knowledge, the capacity to select in the best way both useful knowledge and the method of processing it, especially in tasks that are carried out fairly frequently, but (2) the time taken to process this information is lengthened owing both to ageing of the central nervous system, and to more fragile short-term memory.

These cognitive functions depend very much on the environment in which the workers have lived, and therefore on their past history, their training, and the work situations which they have had to face. The changes that occur with age are therefore manifested in extremely varied combinations of phenomena of decline and reconstruction, in which each of these two factors may be more or less accentuated.

If in the course of their working lives workers have received only brief training, and if they have had to carry out relatively simple and repetitive tasks, their knowledge will be limited and they have difficulties when confronted with new or relatively unfamiliar tasks. If, moreover, they have to perform work under marked time constraints, the changes that have occurred in their sensory functions and the slowing down of their information processing will handicap them. If, on the other hand, they have had lengthy schooling and training, and if they have had to carry out a variety of tasks, they will thereby have been able to enhance their skills so that the sensory or cognitive deficiencies associated with age will be largely compensated for.

It is therefore easy to understand the role played by continued training in the work situation of ageing workers. Changes in work make it necessary more and more often to have recourse to periodic training, but older workers rarely receive it. Firms frequently do not consider it worthwhile to give training to a worker nearing the end of his or her active life, particularly as learning difficulties are thought to increase with age. And the workers themselves hesitate to undergo training, fearing that they will not succeed, and not always seeing very clearly the benefits that they could derive from training.

In fact, with age, the manner of learning is modified. Whereas a young person records the knowledge transmitted to him, an older person needs to understand how this knowledge is organized in relation to what he or she already knows, what is its logic, and what is its justification for work. He or she also needs time to learn. Therefore one response to the problem of training older workers is, in the first place, to use different teaching methods, according to each person’s age, knowledge and experience, with, in particular, a longer training period for older people.

Ageing of men and women at work

Age differences between men and women are found at two different levels. At the organic level, life expectancy is generally greater for women than for men, but what is called life expectancy without disability is very close for the two sexes—up to 65 to 70 years. Beyond that age, women are generally at a disadvantage. Moreover, women’s maximum physical capacity is on average 30% less than men’s, and this difference tends to persist with advancing age, but the variability in the two groups is wide, with some overlap between the two distributions.

At the level of the working career there are great differences. On average, women have received less training for work than men when they start their working life, they most often occupy posts for which fewer qualifications are needed, and their working careers are less rewarding. With age they, therefore, occupy posts with considerable constraints, such as time constraints and repetitiveness of the work. No sexual difference in the development of cognitive capacity with age can be established without reference to this social context of work.

If the design of work situations is to take account of these gender differences, action must be taken especially in favour of the initial and continuing vocational training of women and constructing work careers that increase women’s experiences and enhance their value. This action must, therefore, be taken well before the end of their active lives.

Ageing of working populations: the usefulness of collective data

There are at least two reasons for adopting collective and quantitative approaches with respect to the ageing of the working population. The first reason is that such data will be necessary in order to evaluate and foresee the effects of ageing in a workshop, a service, a firm, a sector or a country. The second reason is that the main components of ageing are themselves phenomena subject to probability: all workers do not age in the same way or at the same rate. It is therefore by means of statistical tools that various aspects of ageing will sometimes be revealed, confirmed or assessed.

The simplest instrument in this field is the description of age structures and of their evolution, expressed in ways relevant to work: economic sector, trade, group of jobs, and so on.

For example, when we observe that the age structure of a population in a workplace remains stable and young, we may ask which characteristics of the work could play a selective role in terms of age. If, on the contrary, this structure is stable and older, the workplace has the function of receiving people from other sectors of the firm; the reasons for these movements are worth studying, and we should equally verify whether the work in this workplace is suited to the characteristics of an ageing workforce. If, finally, the age structure shifts regularly, simply reflecting recruitment levels from one year to another, we probably have a situation where people “grow old on site”; this sometimes requires special study, particularly if the annual number of recruitments is tending to decline, which will shift the overall structure towards higher age groups.

Our understanding of these phenomena can be enhanced if we have quantitative data on working conditions, on the posts currently occupied by the workers and (if possible) on the posts that they no longer occupy. The work schedules, the repetitiveness of work, the nature of the physical demands, the work environment, and even certain cognitive components, can be the subject of queries (to be asked of the workers) or of evaluations (by experts). It is then possible to establish a connection between the characteristics of the present work and of past work, and the age of the workers concerned, and so to elucidate the selection mechanisms to which the work conditions can give rise at certain ages.

These investigations can be further improved by also obtaining information on the health status of the workers. This information can be derived from objective indicators such as the work accident rate or sickness absence rate. But these indicators often require considerable care as regards methodology, because although they do indeed reflect health conditions that may be work-related, they also reflect the strategy of all those concerned with occupational accidents and absence due to illness: the workers themselves, the management and the physicians can have various strategies in this regard, and there is no guarantee that these strategies are independent of the worker’s age. Comparisons of these indicators between ages are therefore often complex.

Recourse will therefore be had, when possible, to data arising from self-evaluation of health by the workers, or obtained during medical examinations. These data may relate to diseases whose variable prevalence with age needs to be better known for purposes of anticipation and prevention. But the study of ageing will rely above all on the appreciation of conditions that have not reached the disease stage, such as certain types of functional deterioration: (e. g., of the joints—pain and limitation of sight and hearing, of the respiratory system) or else certain kinds of difficulty or even incapacity (e. g. in mounting a high step, making a precise movement, maintaining equilibrium in an awkward position).

Relating data concerning age, work and health is therefore at the same time a useful and complex matter. Their use permits various types of connections to be revealed (or their existence to be presumed). It may be a case of simple causal relationships, with some requirement of the work accelerating a type of decline in the functional state as age advances. But this is not the most frequent case. Very often, we shall be led to appreciate simultaneously the effect of an accumulation of constraints on the a set of health characteristics, and at the same time the effect of selection mechanisms in accordance with which workers whose health has declined may find that they are excluded from certain kinds of work (what the epidemiologists call the “healthy worker effect”).

In this way we can evaluate the soundness of this collection of relationships, confirm certain fundamental knowledge in the sphere of psychophysiology, and above all obtain information that is useful for devising preventive strategies as regards ageing at work.

Some types of action

Action to be undertaken to maintain ageing workers in employment, without negative consequences for them, must follow several general lines:

1. One must not consider this age group as a category apart, but must instead consider age as one factor of diversity among others in the active population; protective measures that are too targeted or too accentuated tend to marginalize and weaken the position of the populations concerned.
2. One should anticipate individual and collective changes related to age, as well as changes in work techniques and organization. The management of human resources can be effectively carried out only over time, so as to prepare appropriate adjustments in work careers and training. The design of work situations can then take account at the same time of the available technical and organizational solutions and the characteristics of the (future) population concerned.
3. The diversity of individual development throughout working life should be taken into consideration, so as to create conditions of equivalent diversity in work careers and situations.
4. Attention should be devoted to favouring the process of building up skills and attenuating the process of decline.

On the basis of these few principles, several types of immediate action can first be defined. The highest priority of action will concern working conditions that are capable of posing particularly acute problems for older workers. As mentioned earlier, postural stresses, extreme exertion, strict time constraints (e.g., as with assembly-line work or the imposition of higher output goals), harmful environments (temperature, noise) or unsuitable environments (lighting conditions), night work and shift work are examples.

Systematic pinpointing of these constraints in posts that are (or may be) occupied by older workers allows an inventory to be drawn up and priorities to be established for action. This pinpointing can be carried out by means of empirical inspection checklists. Of equal use will be analysis of worker activity, which will permit observation of their behaviour to be linked with the explanations that they give of their difficulties. In these two cases, measures of effort or of environmental parameters may complete the observations.

Beyond this pinpointing, the action to be taken cannot be described here, since it will obviously be specific to each work situation. The use of standards may sometimes be useful, but few standards take account of specific aspects of ageing, and each one is concerned with a particular domain, which tends to give rise to thinking in an isolated fashion about each component of the activity under study.

Apart from the immediate measures, taking ageing into account implies longer-range thinking directed towards working out the widest possible flexibility in the design of work situations.

Such flexibility must first be sought in the design of work situations and equipment. Restricted space, nonadjustable tools, rigid software, in short, all the characteristics of the situation that limit the expression of human diversity in the carrying out of the task are very likely to penalize a considerable proportion of older workers. The same is true of the more constraining types of organization: a completely predetermined distribution of tasks, frequent and urgent deadlines, or too numerous or too strict orders (these, of course, must be tolerated when there are essential requirements relating to the quality of production or the safety of an installation). The search for such flexibility is, therefore, the search for varied individual and collective adjustments that can facilitate the successful integration of ageing workers into the production system. One of the conditions for the success of these adjustments is obviously the establishment of work training programmes, provided for workers of all ages and geared to their specific needs.

Taking ageing into account in the design of work situations thus entails a series of coordinated actions (overall reduction in extreme stresses, using all possible strategies for work organization, and continuous efforts to increase skills), which are all the more efficient and all the less expensive when they are taken over the long term and are carefully thought out in advance. The ageing of the population is a sufficiently slow and foreseeable phenomenon for appropriate preventive action to be perfectly feasible.

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Designing for Disabled Persons is Designing for Everyone

There are so many products on the market that readily reveal their unfitness for the general population of users. What evaluation should one make of a doorway too narrow to comfortably accommodate a stout person or pregnant woman? Shall its physical design be faulted if it satisfies all relevant tests of mechanical function? Certainly such users cannot be regarded as disabled in any physical sense, since they may be in a state of perfect health. Some products need considerable handling before one can force them to perform as desired—certain inexpensive can openers come, not altogether trivially, to mind. Yet a healthy person who may experience difficulty operating such devices need not be considered disabled. A designer who successfully incorporates considerations of human interaction with the product enhances the functional utility of his or her design. In the absence of good functional design, people with a minor disability may find themselves in the position of being severely hampered. It is thus the user-machine interface that determines the value of design for all users.

It is a truism to remind oneself that technology exists to serve human beings; its use is to enlarge their own capabilities. For disabled persons, this enlargement has to be taken some steps further. For instance in the 1980s, a good deal of attention was paid to the design of kitchens for disabled people. The experience gained in this work penetrated design features for “normal” kitchens; the disabled person in this sense may be considered a pioneer. Occupationally-induced impairments and disabilities—one has but to consider the musculoskeletal and other complaints suffered by those confined to sedentary tasks so common in the new workplace—similarly call for design efforts aimed not only also preventing the recurrence of such conditions, but at the development of user-compatible technology adapted to the needs of workers already affected by work-related disorders.

The Broader Average Person

The designer should not focus on a small, unrepresentative population. Among certain groups it is most unwise to entertain assumptions concerning similarities among them. For example, a worker injured in a certain way as an adult may not necessarily be anthropometrically quite so different from an otherwise comparable, healthy person, and may be considered as part of the broad average. A young child so injured will display a considerably different anthropometry as an adult since his muscular and mechanical development will be steadily and sequentially influenced by preceding growth stages. (No conclusions as to comparability as adults ought to be ventured as regards the two cases. They must be regarded as two distinct, specific groups, only the one being included among the broad average.) But as one strives for a design suitable for, say, 90% of the population, one should exert fractionally greater pains to increase this margin to, say, 95%, the point being that in this way the need for design for specific groups can be reduced.

Another way to approach design for the broader average population is to produce two products, each one designed roughly to fit the two percentile extremes of human differences. Two sizes of chair, for instance, might be built, the one with brackets allowing it to be adjusted in height from 38 to 46 cm, and the other one from 46 to 54 cm; two sizes of pliers already exist, one fitting larger and average sizes of men’s hands and the other fitting average women’s hands and hands of smaller men.

It would be a well-advised company policy to reserve annually a modest amount of money to have worksites analysed and made more suitable for workers, a move that would prevent illness and disability due to excessive physical load. It also increases the motivation of workers when they understand that management is actively trying to improve their work environment, and more impressively so when elaborate measures sometimes have to be undertaken: thorough work analysis, the construction of mock-ups, anthropometrical measurements, and even the specific design of units for the workers. In a certain company, in fact, the conclusion was that the units should be redesigned at every worksite because they caused physical overload in the form of too much standing, there were unsuitable dimensions associated with the seated positions, and there were other deficiencies as well.

Costs, Benefits and Usability of Design

Cost/benefit analyses are developed by ergonomists in order to gain insight into the results of ergonomic policies other than those that are economic. In the present day, evaluation in the industrial and commercial realms includes the negative or positive impact of a policy on the worker.

Methods of evaluating quality and usability are currently the subject of active research. The Rehabilitation Technology Useability Model (RTUM), as shown in figure 1, can be utilized as a model for evaluating the usability of a product within rehabilitation technology and to illuminate the various aspects of the product which determine its usability.

Figure 1. The Rehabilitation Technology Useability Model (RTUM)

From the strictly economic point of view, the costs of creating a system in which a given task can be performed or in which a certain product can be made can be specified; it scarcely needs mentioning that in these terms each company is interested in a maximum return on its investment. But how can the real costs of task performance and product manufacturing in relation to financial investment be determined when one takes into account the varying exertions of workers’ physical, cognitive and mental systems? In fact, the judging of human performance itself is, among other factors, based on the workers’ perception of what has to be done, their view of their own value in doing it, and their opinion of the company. It is actually the intrinsic satisfaction with work that is the norm of value in this context, and this satisfaction, together with the aims of the company, constitute one’s reason for performing. Worker well-being and performance are thus based on a wide spectrum of experiences, associations and perceptions that determine attitudes towards work and the ultimate quality of performance—an understanding upon which the RTUM model is predicated.

If one does not accept this view, it becomes necessary to regard investment only in relation to doubtful and unspecified results. If ergonomists and physicians wish to improve the work environment of disabled people—to produce more from machine operations and enhance the usability of the tools used—they will encounter difficulties in finding ways to justify the financial investment. Typically, such justification has been sought in savings realized by prevention of injury and illness due to work. But if the costs of illness have been borne not by the company but by the state, they become financially invisible, so to speak, and are not seen as work-related.

Nevertheless, the awareness that investment in a healthy working environment is money well spent has been growing with the recognition that the “social” costs of incapacities are translatable in terms of ultimate costs to a country’s economy, and that value is lost when a potential worker is sitting about at home making no contribution to society. Investing in a workplace (in terms of adapting a work station or providing special tools or perhaps even help in personal hygiene) can not only reward a person with job satisfaction but can help make him or her self-sufficient and independent of social assistance.

Cost/benefit analyses can be carried out in order to determine whether special intervention in the workplace is justified for disabled persons. The following factors represent sources of data that would form the object of such analyses:

1. Personnel

• Absence. Will the disabled worker have a satisfactory attendance record?

• Is it likely that extra costs may be incurred for special task instruction?

• Are personnel changes called for? Their costs must be considered also.

• Can accident compensation rates be expected to increase?

2. Safety

• Will the job being considered for the disabled worker involve safety regulations?

• Will special safety regulations be involved?

• Is the work characterized by a considerable frequency of accidents or near accidents?

3. Medical

• As regards the worker whose disability is being examined with a view to his or her re-entry into the workplace, the nature and seriousness of the incapacity must be assessed.

• The extent of the disabled worker’s absence must also be taken into account.

• What is the character and frequency of the worker’s “minor” symptoms, and how are they to be dealt with? Can the future development of related “minor” illnesses capable of hampering the worker’s efficiency be foreseen?

As concerns time lost from work, these calculations can be made in terms of wages, overhead, compensation and lost production. The sort of analyses just described represents a rational approach by which an organization can arrive at an informed decision as to whether a disabled worker is better off back on the job and whether the organization itself will gain by his or her return to work.

In the preceding discussion, designing for the broader population has received a focus of attention heightened by emphasis on specific design in relation to usability and the costs and benefits of such design. It is still a difficult task to make the needed calculations, including all relevant factors, but at present, research efforts are continuing that incorporate modelling methods in their techniques. In some countries, for example the Netherlands and Germany, government policy is making companies more responsible for job-related personal harm; fundamental changes in regulatory policies and insurance structures are, clearly, to be expected to result from trends of this sort. It has already become a more or less settled policy in these countries that a worker who suffers a disabling accident at work should be provided with an adapted work station or be able to perform other work within the company, a policy that has made the treatment of the disabled a genuine achievement in the humane treatment of the worker.

Workers with Limited Functional Capacity

Whether design is aimed at the disabled or at the broader average, it is hindered by a scarcity of research data. Handicapped people have been the subjects of virtually no research efforts. Therefore, in order to set up a product requirements document, or PRD, a specific empirical research study will have to be undertaken in order to gather that data by observation and measurement.

In gathering the information needed about the disabled worker or user it is necessary to consider not only the current functional status of the disabled person, but to make the attempt to foresee whatever changes might be the result of the progression of a chronic condition. This kind of information can, in fact, be elicited from the worker directly, or a medical specialist can supply it.

In designing, for instance, a work action to which data about the worker’s physical strength is relevant, the designer will not choose as a specification the maximum strength which the disabled person can exert, but will take into account any possible diminution in strength that a progression in the worker’s condition might bring about. Thus the worker will be enabled to continue to use the machines and tools adapted or designed for him or at the work station.

Furthermore, designers should avoid designs that involve manipulations of the human body at the far extremes of, say, the range of motion of a body part, but should accommodate their designs to the middle ranges. A simple but very common illustration of this principle follows. A very common part of the drawers of kitchen and office cabinets and desks is a handle that has the form of a little shelf under which one places the fingers, exerting upward and forward force to open the drawer. This manoeuvre requires 180 degrees of supination (with the palm of the hand up) in the wrist—the maximum point for the range of this sort of motion of the wrist. This state of affairs may present no difficulty for a healthy person, provided that the drawer can be opened with a light force and is not awkwardly situated, but makes for strain when the action of the drawer is tight or when the full 180-degree supination is not possible, and is a needless burden on a disabled person. A simple solution—a vertically placed handle—would be mechanically far more efficient and more easily manipulated by a larger portion of the population.

Physical Functioning Ability

In what follows, the three chief areas of limitation in physical functional ability, as defined by the locomotion system, the neurological system and the energy system, will be discussed. Designers will gain some insight into the nature of user/worker constraints in considering the following basic principles of bodily functions.

The locomotion system. This consists of the bones, joints, connective tissues and muscles. The nature of the joint structure determines the range of motion possible. A knee joint, for example, shows a different degree of movement and stability than the joint of the hip or the shoulder. These varying joint characteristics determine the actions possible to the arms, hands, feet, and so on. There are also different types of muscle; it is the type of muscle, whether the muscle passes over one or two joints, and the location of the muscle that determines, for a given body part, the direction of its movement, its speed, and the strength which it is capable of exerting.

The fact that this direction, speed and strength can be characterized and calculated is of great importance in design. For disabled people, one has to take it into account that the “normal” locations of muscles have been disturbed and that the range of motion in joints has been changed. In an amputation, for instance, a muscle may function only partly, or its location may have changed, so that one has to examine the physical ability of the patient carefully to establish what functions remain and how reliable they may be. A case history follows.

A 40-year-old carpenter lost his thumb and the third finger of his right hand in an accident. In an effort to restore the carpenter’s capacity for work, a surgeon removed one of the patient’s great toes and he replaced the missing thumb with it. After a period of rehabilitation, the carpenter returned to work but found it impossible to do sustained work for more than three to four hours. His tools were studied and found to be unfitted to the “abnormal” structure of his hand. The rehabilitation specialist, examining the “redesigned” hand from the point of view of its new functional ability and form was able to have new tools designed that were more appropriate and usable with respect to the altered hand. The load on the worker’s hand, previously too heavy, was now within a usable range, and he regained his ability to continue work for a longer time.

The neurological system. The neurological system can be compared to a very sophisticated control room, complete with data collectors, whose purpose it is to initiate and govern one’s movements and actions by interpreting information relating to those aspects of the body’s components relating to position and mechanical, chemical and other states. This system incorporates not only a feedback system (e.g., pain) that provides for corrective measures, but a “feed-forward” capability which expresses itself anticipatorily so as to maintain a state of equilibrium. Consider the case of a worker who reflexively acts so as to restore a posture in order to protect himself from a fall or from contact with dangerous machine parts.

In disabled persons, the physiological processing of information can be impaired. Both the feedback and the feed-forward mechanisms of visually impaired people are weakened or absent, and the same is true, on an acoustic level, among the hearing-impaired. Furthermore the important governing circuits are interactive. Sound signals have an effect on the equilibrium of a person in conjunction with proprioceptive circuits that situate our bodies in space, so to speak, via data gathered from muscles and joints, with the further help of visual signals. The brain can function to overcome quite drastic deficiencies in these systems, correcting for errors in the coding of information and “filling in” missing information. Beyond certain limits, to be sure, incapacity supervenes. Two case histories follow.

Case 1. A 36-year-old woman suffered a lesion of the spinal cord due to an automobile accident. She is able to sit up without assistance and can move a wheelchair manually. Her trunk is stable. The feeling in her legs is gone, however; this defect includes an inability to sense temperature changes.

She has a sitting workplace at home (the kitchen is designed to allow her to work in a seated position). The safety measure has been taken of installing a sink in a position sufficiently isolated that the risk of burning her legs with hot water is minimized, since her inability to process temperature information in the legs leaves her vulnerable to being unaware of being burned.

Case 2. A five-year-old boy whose left side was paralysed was being bathed by his mother. The doorbell rang, the mother left the boy alone to go to the front door, and the boy, turning on the hot-water tap, suffered burns. For safety reasons, the bath should have been equipped with a thermostat (preferably one that the boy could not have overridden).

The energy system. When the human body has to perform physical labour, physiological changes, notably in the form of interactions in the muscle cells, take place, albeit relatively inefficiently. The human “motor” converts only about 25% of its energy supply to mechanical activity, the remainder of the energy representing thermal losses. The human body is therefore not especially suited to heavy physical labour. Exhaustion sets in after a certain time, and if heavy labour has to be performed, reserve energy sources are drawn upon. These sources of reserve energy are always used whenever work is carried out very rapidly, is started suddenly (without a warm-up period) or involves heavy exertion.

The human organism obtains energy aerobically (via oxygen in the bloodstream) and anaerobically (after depleting aerobic oxygen, it calls upon small, but important reserve units of energy stored in muscle tissue). The need for fresh air supplies in the workplace naturally draws the focus of discussion of oxygen usage toward the aerobic side, working conditions that are strenuous enough to call forth anaerobic processes on a regular basis being extraordinarily uncommon in most workplaces, at least in the developed countries. The availability of atmospheric oxygen, which relates so directly to human aerobic functioning, is a function of several conditions:

• Ambient air pressure (approximately 760 torr, or 21.33 kPa at sea level). High-altitude task performance can be profoundly affected by oxygen deficiency and is a prime consideration for workers in such conditions.

• For workers doing heavy labour, ventilation is necessary to ensure refreshment of the air supply, allowing the volume of air respired per minute to be increased.

• Ambient oxygen makes its way into the bloodstream via the alveoli by diffusion. At higher blood pressures, the diffusion surface is enlarged and thereby the oxygen capacity of the blood.

• An increase in oxygen diffusion to the tissues causes an increase of the diffusion surface and consequently of the oxygen level.

• People with certain heart problems suffer when, with increased cardiac output (together with the oxygen level), the blood circulation changes in favour of the muscles.

• By contrast with oxygen, because of the large reserves of glucose, and especially fat, the energy source (“fuel”) need not be continuously delivered from the outside. In heavy labour, it is merely glucose, with its high energy value, that is used. With lighter work, fat is called upon, at a rate varying with the individual. A brief, general case history follows.

A person suffering from asthma or bronchitis, both of which are diseases affecting the lungs, causes the worker severe limitation in his or her work. The work assignment of this worker should be analysed with respect to factors such as physical load. The environment should be analysed as well: clean ambient air will contribute substantially to workers’ well-being. Furthermore, the workload should be balanced through the day, avoiding peak loads.

Specific Design

In some cases, however, there is still a need for specific design, or design for very small groups. Such a need arises when the tasks to be performed and the difficulties a disabled person is experiencing are excessively large. If the needed specific requirements cannot be made with the available products on the market (even with adaptations), specific design is the answer. Whether this sort of solution may be costly or cheap (and aside from humanitarian issues) it must be nonetheless regarded in the light of workability and support to the firm’s viability. A specially designed worksite is worthwhile economically only when the disabled worker can look forward to working there for years and when the work he or she does is, in production terms, an asset to the company. When this is not the case, although the worker may indeed insist upon his or her right to the job, a sense of realism should prevail. Such touchy problems should be approached in a spirit of seeking a solution by cooperative endeavours at communication.

The advantages of specific design are as follows:

• The design is custom made: it fits the problems to be solved to perfection.

• The worker so served can return to work and a life of social participation.

• The worker can be self-sufficient, independent of welfare.

• The costs of any personnel changes that the alternative might involve are avoided.

The disadvantages of specific design are:

• The design is unlikely to be used for even one other person, let alone a larger group.

• Specific design is often costly.

• Specifically designed products must often be handmade; savings owing to mass methods are most often not realizable.

Case 1. For example, there is the case of a receptionist in a wheelchair who had a speech problem. Her speech difficulty made for rather slow conversations. While the firm remained small, no problems arose and she continued to work there for years. But when the firm enlarged, her disabilities began to make themselves problematic. She had to speak more rapidly and to move about considerably faster; she could not cope with the new demands. However, solutions to her troubles were sought and reduced themselves to two alternatives: special technical equipment might be installed so that the deficiencies that degraded the quality of some of her tasks could be compensated for, or she could simply choose a set of tasks involving a more desk-bound workload. She chose the latter course and still works for the same company.

Case 2. A young man, whose profession was the production of technical drawings, suffered a high level spinal cord lesion due to diving in shallow waters. His injury is severe enough for him to require help with all his daily activities. Nevertheless, with the help of a computer-aided design (CAD) software, he continues to be able make his living at technical drawing and lives, financially independent, with his partner. His work space is a study adapted for his needs and he works for a firm with which he communicates by computer, phone and fax. To operate his personal computer, he had to have certain adaptations made to the keyboard. But with these technical assets he can earn a living and provide for himself.

The approach for specific design is not different from other design as described above. The only insurmountable problem that may arise during a design project is that the design objective cannot be achieved on purely technical grounds—in other words, it can’t be done. For example, a person suffering from Parkinson’s disease is prone, at a certain stage in the progression of his or her condition, to fall over backwards. An aid which would prevent such an eventuality would of course represent the desired solution, but the state of the art is not such that such a device can yet be built.

System Ergonomic Design and Workers with Special Physical Needs

One can treat bodily impairment by medically intervening to restore the damaged function, but the treatment of a disability, or deficiency in the ability to perform tasks, can involve measures far less developed in comparison with medical expertise. As far as the necessity of treating a disability is concerned, the severity of the handicap strongly influences such a decision. But given that treatment is called for, however, the following means, taken singly or in combination, form the choices available to the designer or manager:

• leaving out a task

• compensating for a worker’s deficiency in performing a task element by using a machine or another person’s help

• differentiation of the task order, that is, dividing the task into more manageable subtasks

• modification of the tools used in the task

• special design of tools and machines.

From the specific ergonomic point of view, treatment of a disability includes the following:

• modification of the task

• modification of a tool

• design of new tools or new machines.

The issue of efficacy is always the point of departure in the modification of tools or machines, and is often related to the costs devoted to the modification in question, the technical features to be addressed, and the functional changes to be embodied in the new design. Comfort and attractiveness are qualities that by no means deserve to be neglected among these other characteristics.

The next consideration relating to design changes to be made to a tool or machine is whether the device is one already designed for general use (in which case, modifications will be made to a pre-existing product) or is to be designed with an individual type of disability in mind. In the latter case, specific ergonomic considerations must be devoted to each aspect of the worker’s disability. For example, given a worker suffering from limitations in brain function after a stroke, impairments such as aphasia (difficulty in communication), a paralysed right arm, and a spastic paresis of the leg preventing its being moved upwards might require the following adjustments:

• a personal computer or other device enabling the worker to communicate

• tools that can be operated with the remaining useful arm

• a prosthetic system that would serve to restore the function of the impaired foot as well as to compensate for the patient’s loss of ability to walk.

Is there any general answer to the question of how to design for the disabled worker? The system ergonomic design (SED) approach is an eminently suitable one for this task. Research related to the work situation or to the kind of product at issue requires a design team for the purpose of gathering special information relating either to a special group of disabled workers or to the unique case of an individual user disabled in a particular way. The design team will, by virtue of including a diversity of qualified people, be in possession of expertise beyond the technical sort expected of a designer alone; the medical and ergonomic knowledge shared among them will be as fully applicable as the strictly technical.

Design constraints determined by assembling data related to disabled users are treated with the same objectivity and in the same analytical spirit as are counterpart data relating to healthy users. Just as for the latter, one has to determine for disabled persons their personal patterns of behavioural response, their anthropometrical profiles, biomechanical data (as to reach, strength, range of motion, handling space used, physical load and so forth), ergonomic standards and safety regulations. But one is most regretfully obliged to concede that very little research indeed is done on behalf of disabled workers. There exist a few studies on anthropometry, somewhat more on biomechanics in the field of prostheses and orthoses, but hardly any studies have been carried on physical load capabilities. (The reader will find references to such material in the “Other relevant reading” list at the end of this chapter.) And while it is sometimes easy to gather and apply such data, frequently enough the task is difficult, and in fact, impossible. To be sure, one must obtain objective data, however strenuous the effort and unlikely the chances of doing so, given that the numbers of disabled persons available for research is small. But they are quite often more than willing to participate in whatever research they are offered the opportunity of sharing in, since there is great consciousness of the importance of such a contribution towards design and research in this field. It thus represents an investment not only for themselves but for the larger community of disabled people.

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