Defining and measuring long COVID fatigue: a scoping review

Long COVID encompasses a range of symptoms in which fatigue is one of the most prevalents. It is clear from other conditions that the definition and measurement of fatigue can be complex, but it is not clear how fatigue is defined and measured in long COVID. To advance our understanding, this review summarises the definitions and measures of long COVID fatigue being used by researchers.

Scoping review following JBI methodology and reports using the Preferred Reporting Items for Systematic Reviews and Meta-analyses extension for scoping reviews.

Medline, Scopus, CINAHL, PsycINFO, EMCARE, Web of Science, Epistemonikos, Cochrane Central Register of Controlled Trials, Dimensions, Overton and ProQuest Dissertation & Theses Database were searched from January 2020 to May 2023.

This review included quantitative and qualitative studies that included any definition of long COVID and/or measurement tool that purported to quantify either the impact, severity or symptoms of long COVID fatigue.

Two independent reviewers screened the title, abstracts and full texts of the selected studies based on the inclusion criteria. Data extraction was performed by two independent reviewers. The data were summarised in tabular format and a narrative summary.

The search retrieved 9839 studies, of which 57 met the inclusion criteria. Only 21 (37%) provided a definition of fatigue. Definitions ranged across physical, mental, cognitive, emotional, psychosocial, central, peripheral, postexertional symptom exacerbation and general dimensions of fatigue. Fifty-five (96%) used a measurement or assessment of fatigue. Twenty-six measures of fatigue were identified: 21 self-report measures (eg, Fatigue Assessment Scale) and five fatigability measures that purport to reflect changes in physiological processes that contribute to or reflect fatigue (eg, change in force generating capacity of a muscle).

The definitions identified demonstrate considerable diversity, each highlighting different dimensions of long COVID fatigue. Long COVID fatigue was predominantly measured through self-report methods, which were problematic. There is an urgent need to better understand long COVID fatigue and to identify the different mechanisms involved. In order to do this, we need consistency with the language around fatigue and its measurement within research and across disciplines.

The protocol has been registered on open science framework (https://doi.org/10.17605/OSF.IO/HNF8Z).