AUTHOR=Skau Simon , Sundberg Kristoffer , Kuhn Hans-Georg TITLE=A Proposal for a Unifying Set of Definitions of Fatigue JOURNAL=Frontiers in Psychology VOLUME=Volume 12 - 2021 YEAR=2021 URL=https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2021.739764 DOI=10.3389/fpsyg.2021.739764 ISSN=1664-1078 ABSTRACT=In this paper, we propose a set of unifying definitions that are useful in all areas of fatigue research while remaining neutral to the various theories about fatigue. We first set up two criteria and four desid-erata that a definition for interdisciplinary use needs to fulfill: i) non-circularity, ii) finiteness, iii) broad-ness, iv) precision, v) neutrality, and vi) phenomena-focused. We argue that other existing attempts to unify definitions within fatigue research do not fulfill all of these criteria and desiderata . Instead, we argue for a set of stipulative definitions, centered around performance measures and subjective estima-tions, is required in order to maximize clarity. In total, a set of 17 distinct definitions of fatigue and fa-tigue-related phenomena is presented. These definitions will help facilitate communication between dif-ferent researchers, link phenomena from divergent research fields together, facilitate application and knowledge production, and increase the specificity for hypothesis testing.