Fatigue is hard to define. In the nineteenth century, Beard (1880) referred to fatigue as ‘the Central Africa of medicine, an unexplored territory which few men enter’. Unfortunately, fatigue still remains a vague and difficult concept to define. Nevertheless, it is likely that most people will experience fatigue at one or more times in their lives. It can present in a multitude of ways, with a myriad of personal experiences and descriptions, such as mental exhaustion, lack of motivation, physical tiredness and weariness. Increasingly in the older population, fatigue is identified as having consequences both for quality of life and mortality.

Fatigue is rarely a binary state, i.e. one has fatigue or one does not. At different times, everyone may experience levels of fatigue varying from mild to overwhelming. Within the concepts of fatigue, it is also important to consider a number of other descriptors of fatigue, namely normal, abnormal, peripheral, or central, in addition to the differing dimensions of fatigue. There is a clear distinction between peripheral and central fatigue. Peripheral fatigue is defined as a reduction in the maximal muscle force or motor output and is commonly due to overexertion, prolonged or strenuous physical activity. Central fatigue conversely refers to the general feeling often described as ‘tiredness’, ‘weakness’, ‘languor’, or ‘sleepiness’. This may exist independently or may be due to some underlying psychological or pathological condition, as outlined in Table 62.1. It is accepted that ‘normal’ fatigue is a state of general tiredness that is the result of overexertion and can be ameliorated by rest. In contrast, ‘abnormal’ or ‘pathologic’ fatigue is a state characterized by weariness unrelated to previous exertion levels and is usually not ameliorated by rest. Both peripheral and central fatigue may exist in normal and abnormal states. This discussion focuses on this general tiredness and lack of motivation associated with central fatigue.

Ream and Richardson (1996), in a large-scale concept analysis review of fatigue literature, assimilated the pertinent information on fatigue in its various forms and proposed a clarified definition for the otherwise amorphous concept. The authors suggest ‘fatigue is a subjective, unpleasant symptom which incorporates total body feelings ranging from tiredness to exhaustion creating an unrelenting overall condition which interferes with an individual’s ability to function to their normal capacity’. Further searches for an adequate definition have added to this explanation and a review of these definitions by Yu et al. (2010) concluded simply that the overall fatigue experienced among older adults is a ‘debilitating compromise of quality of life’. Following a systematic search of the literature relating to fatigue among older people, they identified 15 relevant studies and 3 main aspects of reported fatigue: the lived experience of fatigue, relating factors of fatigue and impact of fatigue on overall health. They cautioned that the complexity of this phenomenon, in terms of its ‘ubiquitous nature, heterogeneous etiologies, and multidimensional manifestation imposes real challenges to health professionals in managing this distressing symptom’.

Krupp (2003) suggests that the experience of fatigue reported by a patient may also be interpreted in different ways by different healthcare professionals – physiotherapists, oncologists, nurses, occupational therapists and neurologists. Nevertheless, she goes on to suggest that fatigue can be conceptualized in a number of different ways, included in Box 62.1. Fatigue is not one-dimensional; many authors report the importance of the various dimensions of fatigue. In designing an instrument to measure fatigue, Smets et al. (1995) identified five discernible dimensions of fatigue, which are general fatigue, physical fatigue, reduction in activity, reduction in motivation and mental fatigue.

The findings are contradictory: Beutel et al. (2004) observed, in a large sample of women, that all five dimensions of fatigue described above increased gradually over time. However, Watt et al. (2000), investigating the levels of fatigue in people aged 20–79 years in a population-based study, found that most dimensions of fatigue decreased with age among healthy people, compared with an increase with age in the group with disease. Older people living in long-term care facilities may experience more fatigue symptoms (Liao & Ferrell, 2000). In 2007, Wijeratne et al. reported that 27% of people over 60 attending a primary care setting reported fatigue, which they subsequently determined was largely independent of physical or psychological illness. Hence, all people, both ill and healthy alike, old and young, may experience fatigue. The likelihood of experiencing fatigue is increased in people suffering from a range of different medical conditions. These conditions are listed in Box 62.1, many of which can be more common in people over 65 years of age. It is probably more helpful to focus on what self-reported fatigue or tiredness is associated with, or a predictor of, in later life.

What of the effect of this fatigue? Avlund et al. (1998) note that self-reported tiredness in functional mobility in people aged 70 years is strongly predictive of mortality during the following 10 years, even when disability at baseline is considered. This was echoed 10 years later in a study by Hardy and Studenski (2008) in which self-reported tiredness, as a measure of fatigue, was related to increased mortality over 10 years. The influence of fatigue was shown to be almost as great as that of diabetes or heart disease. The study assessed fatigue with the question ‘during the past month, have you felt tired most of the time?’ The authors acknowledge that this measure of fatigue may not encompass all aspects of the condition; however, it is a clinically useful and easy-to-administer method to gain an insight into fatigue. Avlund et al. (2002) also noted a predictive association between people aged 75 years who report tiredness in 4 lower limb activities and onset of disability in the following 5 years. This association exists even when other variables associated with onset of disability are considered in the analysis. In this sample, Avlund et al. (2001) also noted that men and women who self-reported tiredness in functional mobility at 75 years of age were twice as likely to be hospitalized in the year prior to follow-up, i.e. at 80 years, and were also more likely to use home help services. Fatigue was determined to be an early indicator of functional decline, as measured by a loss in walking speed, in a 5-year follow-up study of 292 adults aged 75 (Manty et al., 2012).

It is important to take seriously reports of tiredness or fatigue by older people. Hence, measuring fatigue or tiredness in older people and exploring the reasons for its presence are significant because its report may be an early marker of coexisting disease or a decrease in functional reserve. If present, early intervention may prevent functional decline and/or highlight the need for more substantive evaluation.

Owing to the elusiveness of a precise definition of fatigue in the literature, an individual’s reported perception of his or her fatigue has become the focus of fatigue measurement. These self-report scales have therefore become widely used. They also have the advantage of being easily understandable by the patient and requiring little prior training by the assessor. They are usually short and readily available. Self-report measures have different structures, from simple unidimensional measures such as the Visual Analog Fatigue Scale (Glaus, 1993) to more complex measures encompassing the multidimensional nature of fatigue, such as the Multidimensional Fatigue Inventory (Smets et al., 1995). Debate continues as to the most useful tool to assess fatigue. The multidimensional measures capture the subtleties of the symptom, perhaps affording more sensitivity to change; however, they often benefit from the addition of a simple linear scale to quickly assess the patient’s own evaluation of the impact of the symptom. Among the studies mentioned here, a range of self-report measurement tools have been utilized, from a simple polar question, as used by Hardy and Studenski (2008), to the six-point Avlund Mobility-Tiredness scale (Manty et al., 2012) and the popular Multidimensional Fatigue Inventory (Watt et al., 2000; Beutel et al., 2004), which is further explained below.

Table 62.2 contains some of the commonly used self-report scales, along with the populations in which they have been validated. One particular measure of value for use with older people is the Multidimensional Fatigue Inventory (MFI-20) (Smets et al., 1995). The Multidimensional Fatigue Inventory is a 20-item self-report instrument that acknowledges the comprehensive nature of fatigue. It divides fatigue into the following dimensions: general fatigue, physical fatigue, mental fatigue, reduced motivation and reduced activity. It has been validated in both healthy older people and those with a range of common conditions. The creators found the instrument to have good internal consistency and construct validity (Smets et al., 1995). The MFI-20 is copyrighted on the names of the authors and is reproduced here with permission (Form 62.1). The scoring system and conditions of use are available from Dr E.M.A. Smets, Medical Psychology Academic Medical Center, University of Amsterdam, PO Box 22660, 1100 DD, Amsterdam, The Netherlands, e-mail: e.m.smets@amc.uva.nl.