Fatigue has been defined as the “unconscious decreased ability for physical and or mental activity due to an imbalance in availability, utilization or the retrieval of the physiological or psychological resources required to perform the activity” p.2 (Aaronson et al. 1999). Those studying or reporting on fatigue have attempted to distinguish between physical and psychological fatigue (Aaronson et al. 1999). Physical fatigue has been defined as “the result of excessive energy consumption, depleted hormones or neurotransmitters or diminished ability of muscle cells to contract”p.2 (Jha et al. 2008). Psychological fatigue has been defined as “a state of wariness related to reduced motivation, prolonged mental fatigue or boredom” p.1 (Lee et al. 1991).

A meta-analysis conducted by Mathias and Alvaro (2012) found that 50% of people with TBI experience disturbed sleep. Common sleep complaints among individuals with moderate to severe brain injury are poor sleep quality, longer sleep-onset latency, increased nocturnal awakening, and insomnia (Duclos et al. 2014; Grima et al. 2016). Unfortunately there is large variability in the estimates of fatigue and sleep disorders within the ABI literature, much of which is due to variation in how data is collected. Both subjective and objective means of collecting this data are available. A systematic review found 16 measures of fatigue were commonly used in TBI studies (Mollayeva et al. 2013). Most common is the utilization of questionnaires, but polysomnography, actigraphy, multiple sleep latency tests, and maintenance of wakefulness tests are objective measures that may be used (Mollayeva et al. 2013).

Although it would seemingly make sense to link disorders of sleep with fatigue (Clinchot et al. 1998), this relationship remains inconclusive (Fellus & Elovic 2007). Sleep disturbances can exacerbate fatigue, however fatigue may also manifest independent of sleep disorders (Ouellet et al. 2015). There are many plausible sources of fatigue including neuroanatomical, functional, psychological, biochemical or endocrine causes (Mollayeva et al., 2013). A review by Duclos et al. (2014) suggests that sleep-wake disturbances may be due to altered circadian rhythms, damage to the cortical and subcortical structures involved, endocrine dysfunction (e.g., growth hormone or cortisol levels), pain, anxiety and depression, or the environment. This complex interplay between psychological, social, environmental and pathophysiological factors interfere with determination of the etiology of sleep disturbances (Ouellet et al. 2015). It is therefore important to investigate the medical and reversible causes of fatigue (e.g., anemia, hypothyroidism, medications that may be worsening fatigue, etc.) in patients with acquired brain injury (ABI). For those recovering from an ABI/traumatic brain injury (TBI), fatigue and sleep disorders have the ability to interfere with an individual’s ability to participate in rehabilitation programs designed to assist them in performing their activities of daily living. It also impacts one’s physical, cognitive and social abilities.

This chapter explores the problems of fatigue and sleep disorders post ABI first by reviewing studies identifying the incidence and prevalence of these symptoms, as well as by summarizing and evaluating studies of treatment interventions for each.