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.

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Biofeedback (BFB) and neurofeedback (NFB) training are two promising approaches for the non-invasive modulation of human physiological activity paired with cognitive, emotional, and behavioral functioning. In this article, we summarize the state of the art with regard to the efficiency of BFB and NFB studies for the optimization of cognitive performance within a non-clinical context. We review the different training protocols with their underlying theoretical perspectives and the different outcomes regarding cognitive performance. This review showed that BFB and NFB are promising training techniques. However, the use of varying terminology to refer to similar concepts, diverse methodological designs, and cognitive assessments along with apparent differences in NFB frequency ranges makes it difficult to compare the outcomes over different studies and to draw general conclusions. Furthermore, a question largely ignored until now remains about the long-term effects of both training and thus the sustainability of the achieved cognitive enhancement.Despite promising results of both techniques, this overview summarizes the encountered issues and formulates suggestions to solve them in order to be able to provide a definitive answer to the title question: Bdo biofeedback and neurofeedback work as a cognitive performance enhancement method?K eywords Nootropic . Biofeedback . Neurofeedback .