Age-associated changes in function

Any attempt at a comprehensive catalogue of age-associated changes and illnesses would easily fill a large textbook. This chapter is necessarily restricted to major topics related to work capacity and to illustrative examples of how illnesses may present in a work-related context.

Physical activity

Muscle mass declines in both sexes from the third decade onwards. As already noted, because women start life with less muscle than men, they are more likely to suffer from limitation in muscle strength and power in later life.⁹ In addition to muscular strength and power, endurance and joint flexibility also decline with age. The last can be partly compensated for by deliberately putting joints through a full range of movement before working.¹⁰ The collective warm-up exercises required of workers in some Far Eastern factories have a physiological as well as ideological function.

Endurance, the ability to maintain high levels of physical activity over prolonged periods, is limited by muscular power and exercise tolerance, and also by pulmonary and cardiac function, all of which decline on average with age. Although breathlessness is usually the dominant symptom in strenuous activity, the limits on exercise capacity are usually muscular or cardiac rather than pulmonary, except in smokers or individuals with lung damage due to other causes.

Older workers in physically strenuous jobs may be working closer to their physical limits than younger colleagues keeping to the same pace, and they may become more readily fatigued. Older workers can cope with heavy muscular exertion,¹¹ so long as the work is interspersed with recovery periods sufficient in frequency and duration, but they find the demands of continuous fast paced lighter work more difficult to sustain. Older workers may prefer to move away from externally paced or ‘piecework’ jobs into hourly paid jobs, if the choice is available. Part of the age- associated loss of muscular function observed in the population is due to lower levels of exercise in older age groups. Training can recover some of the loss by increasing muscle bulk and blood supply, as well as improving muscle metabolism.¹²

Hearing

Some age-associated loss of sensitivity to high frequencies is virtually universal in western societies, and is probably partly due to chronic exposure to noise rather than intrinsic ageing processes.¹³ Those who have worked in noisy industries for many years, with inadequate hearing protection, are almost certain to have significant hearing loss, by the time they reach their midfifties. High frequencies are important in the comprehension of speech but, before the process becomes severe enough to produce overt deafness, it can result in slower ‘decoding’ of speech. This in turn can produce functional cognitive impairment due to slowing of processing and the missing of some information.¹⁴ (Detection and correction of ‘minor’ hearing loss is a necessary first step in the assessment of someone suspected of early dementia.) In the workplace, this effect may be compounded by high ambient noise levels.¹⁵

Sufferers lose the ability accurately to distinguish particular consonants, notably ‘b’, ‘d’, ‘t, and ‘s’ sounds. They may misidentify words or fail to make sense of what they are hearing. An additional problem is difficulty in reliably following one speaker when other voices are also audible, as in many social and work situations. The natural reaction when talking to someone perceived as deaf is to speak more loudly, but this may not help. The sufferer’s cochlea may show a disproportionate response to increase in volume known as ‘recruitment’, and loud sounds can become both painful and distorted. In some working environments, loss of accurate comprehension of verbal instructions will have implications for safety and production costs, if process or other errors result. Some individuals can compensate for hearing loss by lip-reading, and colleagues can be helpful by making use of gesture and facial expression. In some working environments, more use of visual material in the communication of crucial information can improve safety. This becomes easier and more accurate with electronic communication systems. A wide range of adaptive technologies now exist to support the hard of hearing at work (see Chapter 10).

Up to a third of older people suffer from tinnitus, of which the commonest cause is sensorineural deafness due to previous noise exposure. Most people manage to ignore the problem but for others it can become distressing, at least intermittently. The clinician also needs to be alert to recognize depression when it presents as preoccupation with previously ignored tinnitus.

Vision

There are age-associated changes in visual perception, due to both peripheral and central factors. With increasing age, the lens becomes less elastic and the intrinsic muscles weaker, so that accommodation for near vision becomes limited. This effect can begin as young as the mid-forties in otherwise healthy workers and is sometimes a missed cause of what the older worker puts down to ‘eyestrain’. The lens and vitreous of the eye become less transparent and acquire a yellowish tinge that can interfere with colour perception. Owing to the loss of transparency, and also because of changes in the retina, the older eye requires higher light intensities and greater contrast in print for accurate reading. This has important implications for the design of work environments for older employees. Cataracts become common, reducing acuity and also scattering incoming light, causing dazzle. This last factor is especially significant for night driving.

Also relevant to driving safety is a tendency for the functional visual field to contract, so that stimuli in the periphery of vision may not be noticed, even though formal static testing of the visual field shows no defect.¹⁶ This is thought to be one factor in the increase with age in low-speed lateral car collisions at road intersections.¹⁷ Some studies have found it possible to reverse this phenomenon by specific training, and it presumably represents some form of central inattention. Although less clear than in the case of hearing, minor degrees of visual impairment can manifest as slower or less accurate understanding of written material or misinterpretation of environmental cues that can present as apparent cognitive impairment.

Macular degeneration is a further affliction that an older worker may suffer. Treatment is at present of limited benefit and access to advice and suitable visual aids less than perfect. Modifications to computer keyboards and visual display units, and scanning cameras to assist in reading are, however, available and may be of help in prolonging a sufferer’s working life.

Touch and proprioception

Dexterity and fineness of touch may deteriorate over time, especially if chronic exposure to trauma leads to thickening of the skin and subcutaneous tissues of the hands. The risk of falls increases in both sexes after the age of 65. The risk is higher, at all ages, in women, who also show a bimodal risk with an earlier transitory peak around the age of 50.¹⁸ Although the risk of falls is related to muscle strength and joint stiffness, as well as any neurological disease, there seems to be a general age-associated impairment of global proprioception.

Proprioception, as tested by standard clinical examination (joint position sense or Romberg test, for example), is unlikely to be manifestly impaired in the absence of specifically diagnosable conditions, such as vitamin B12 deficiency or cervical myelopathy. Global proprioception, in the sense of accurate awareness of the body’s position, orientation, and movement in space, is the product of continuous integration of input from eyes, inner ear, and a range of peripheral proprioceptors, especially in cervical joints, the feet, and the Achilles tendons. As a consequence of degeneration in cervical joints and peripheral nerves, the information from these various sources may be attenuated or may not arrive simultaneously in the central nervous system. In later life, this probably underlies the common symptom of non-rotatory dizziness that is epidemiologically associated with a risk of falls.¹⁹

Mental function

Dementia is rare at ages under 70, except in people with a family history of an early-onset form. There are, however, some differences in mental functioning between middle-aged people and young adults that may need to be considered in matching older workers to occupational tasks (by choosing the workers or designing the tasks) and in developing training programmes. As noted already, some of the differences observed between younger and older workers may be due to cohort effects rather than ageing and so will change with time. One of the first things we learn at school is how to learn, so cohort effects must be expected to be significant in designing training programmes for older workers.

The various processes and aptitudes that comprise human intelligence have been polarized between the ‘crystalline’ and the ‘fluid’. Crystalline intelligence solves problems by applying learned strategies or paradigms. Fluid intelligence solves problems by innovation and analysis from first principles. As we grow older, we tend to rely more on crystalline than on fluid processes. As long as the paradigm chosen, often by recognition of analogies between present and past situations, is appropriate, crystalline intelligence is efficient. It may, however, fail, and indeed be a positive hindrance, in rising to a totally new challenge that requires original thinking. An older individual in a problem-solving situation may need to be made explicitly aware of the need for a new approach, not a ready-made solution from past experience.

Subjectively, the dominant problem in mental ageing is difficulty with memory. It is a clinically useful oversimplification to visualize human memory as comprising an immediate working memory, possibly subserved by active inter-neuronal transmission, linked to a long-term memory based on some permanent neuronal change such as modification of synapses. Some material from the first passes into the second, from whence if adequately filed and labelled, suitable cueing can bring it forth. Both types can show deterioration with age and difficulties with shorter-term memory are obvious enough. In age-associated memory impairment and in the early stages of Alzheimer’s disease, a dominant feature is an apparent problem in the link between shorter-term and longer-term memory, so that material is not written into longer-term store or cannot be recalled from there. This difficulty is commonly, albeit somewhat misleadingly, labelled as a defect in short-term memory—even though the subject’s ability to remember telephone numbers long enough to dial them (‘digit span’) may still be normal.

Increasing attention paid to Alzheimer’s disease in the media has led to middle-aged people with subjective difficulties with memory becoming worried or even depressed, by a fear of incipient dementia, especially those with a family history of dementia, even though the risk for relatives of someone with late-onset dementia is very little higher than average. A middle-aged person manifesting or complaining of memory problems therefore needs skilled and empathetic evaluation. Employers of older workers should encourage the appropriate use of memory supporting strategies—note-taking, notice boards, and electronic prompters, for example. This will help to prevent problems, both directly and also indirectly, so that individuals, fearful of memory loss, do not feel stigmatized by making use of such supportive devices. The value of checklists, for workers of all ages, is formally recognized for airline pilots and surgeons.

Ageing is also associated with a slowing of mental processing and a reduction in channel capacity—essentially the capacity to process several different sequences of data simultaneously and rapidly. Decisions may take longer and mistakes may be made in complex situations. These processes contribute to the rise in accident rates among older car drivers, for example. Compounding the channel capacity problem with ageing is a failure to identify and suppress irrelevant factors when analysing a situation or performing a complex task.