Abstract
Fatigue is such a multifaceted construct it has sprouted specific research fields and experts in domains as different as exercise physiology, cognitive psychology, human factors and engineering, and medical practice. It lacks a consensus definition: it is an experimental concept, a symptom, a risk, a cause (e.g., of performance decrement) and a consequence (e.g., of sleep deprivation). This fragmentation of knowledge leads to slower dissemination of novel insights, and thus to a poorer research. Indeed, what may seem as a novel result in one field, may very well be old news in another, hence leading to this “innovation” being a scientific equivalent to the emperor’s new clothes. The current paper aims to describe the common denominator in the different areas of expertise where fatigue is investigated. Indeed, rather than focusing on the differences in semantics and conceptualization, we hope that identifying common concepts may be inductive of easier multidisciplinary research. Considering the vastness of fatigue research in all areas identified as relevant-cognitive science, exercise physiology, and medical practice, this analysis has not the ambition to be an exhaustive review in all domains. We have reviewed the fatigue concepts and research in these areas and report the ones that are used to describe the proposed common model to be further investigated. The most promising common feature to cognitive science, exercise physiology and clinical practice is the notion of “perceived effort.” This allows to account for interindividual differences, as well as for the situational variations in fatigue. It is applicable to both mental and physical constructs. It integrates motivational and emotional dimensions. It overcomes current polemics in various research fields, and it does not draw on any semantic ambiguity. We thus suggest a new model of fatigue and performance, whether this performance is mental or physical; and whether it is in a clinical range or relates to optimal functioning.
Highlights
Fatigue is typically defined as “extreme and persistent tiredness, weakness or exhaustion-mental, physical or both” (Dittner et al, 2004)
On the other hand, fatigue has traditionally been defined on a peripheral level, as “an acute impairment of exercise performance that leads to an inability to produce maximal force output, possibly due to metabolite accumulation or substrate depletion” (Gibson and Noakes, 2004)
The rationale behind their choice of terminology was based on the reality of the field (most studies in exercise science investigating physical performance after prolonged cognitive activity termed this kind of fatigue as “mental fatigue” (Bray et al, 2008; Brownsberger et al, 2013; MacMahon et al, 2014; Pageaux et al, 2015) and because “mental” suggests a possible role for emotion and motivation rather than just cognition
Summary
Fatigue is typically defined as “extreme and persistent tiredness, weakness or exhaustion-mental, physical or both” (Dittner et al, 2004). As Rabinbach (1992) points out, the medical world acknowledged it as early as 1870, when it was formally recognized as a disease of overwork (not too far away from our current concepts of burn-out) Overall, it was considered as a sign that the human organism has a limited capacity to respond to the demands of modern working life. We have seen a shift form the more traditional attention and vigilance research (Mackworth, 1948; Caldwell, 1995; Dinges et al, 1997), with roots in occupational psychology and sleep research, to a field where mental fatigue is investigated related to the constructs of resource depletion, boredom, and motivation (e.g., Pattyn et al, 2008; Gergelyfi et al, 2015). We present a new model to be used as an investigative framework, merging insights from psychology and physiology; from fundamental research and applied findings
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