Psychosocial mediators of a theory-based resistance training maintenance intervention for prediabetic adults.

One of the most common concerns expressed across physical and mental health patient populations is tiredness []. This has historically been broken down into two distinct phenomena, those of fatigue and sleepiness [, ]. In non-clinical populations fatigue typically reflects a physiological signal that rest is required (with or without sleeping), and is normally the result of energy being expended (e.g. after exercise). Sleepiness is often described as a “behavioural propensity towards sleep” which typically requires resolution by sleeping [, ]. In non-clinical populations fatigue and sleepiness may often co-occur e.g. at the end of the day when the circadian drive for arousal is low and homeostatic sleep pressure is high [, ], and when energy would have been expended. There is an acknowledged difficulty in discriminating between tiredness, sleepiness, and fatigue given that the terms are near-synonymous in common usage [], and there is a lack of appropriate assessment tools to allow accurate discrimination between these presentations [, ]. The underlying mechanisms of fatigue and sleepiness are complex and needing further investigation but are differentiable. Sleepiness is mostly linked with a reduction in inhibition of sleep-promoting systems in the brain []—for example, the orexin system which is disrupted in narcolepsy, leading to sudden sleep attacks []. In contrast, mechanisms underlying fatigue are typically proposed to act across the whole body, with mitochondrial and inflammation-based hypotheses prominent in the current literature []. At the diagnostic level, fatigue and sleepiness may differentiate different sleep disorder indications—for example, insomnia is more strongly associated with fatigue and sleep apnoea with sleepiness [, ]—and therefore differential indicators could assist with discriminating these common conditions. As well as the importance of discriminating between fatigue and sleepiness, better accounting for their overlap would facilitate research addressed at conditions that involve sleepiness and/or fatigue as core elements e.g. chronic fatigue syndrome []. Fatigue and sleepiness are both common alongside mental health problems, and may be linked to worsened symptoms and functioning. Fatigue is strongly associated with depression []. High levels of sleepiness (hypersomnia) are common in mood disorders and may be linked to a more severe clinical profile [, ]. In psychosis fatigue is commonly reported [], and sleepiness is also often problematic []. These symptoms are often ascribed to sedation from medication, but could also be linked to high rates of sleep disorders and low daytime activity [, ].