Measures the severity of fatigue and its impact on daily functioning across nine statements about how fatigue interferes with motivation, exercise, work, family duties, and social activities. Fatigue is among the most common and disabling symptoms across neurological, rheumatological, oncological, and psychiatric conditions, yet is frequently under-assessed. The FSS was developed and validated in multiple sclerosis and lupus but has since been applied across ME/CFS, cancer, depression, COVID-19 long-haul, and many other conditions. Its unidimensional brevity makes it the most widely used fatigue impact measure in clinical research worldwide.
Likert (1–7, strongly disagree to strongly agree); total mean score
Score = mean of all 9 items (1–7). Cut-off score >=4 (or >=5 in some literature) indicates clinically significant fatigue. Freely available. The FSS has been validated across 30+ conditions and is sensitive to change following fatigue management interventions. Widely used as a primary outcome measure in fatigue management trials. A score >=4 differentiates pathological fatigue from normal tiredness in healthy controls.
Krupp, L.B., LaRocca, N.G., Muir-Nash, J., & Steinberg, A.D. (1989). The fatigue severity scale: Application to patients with multiple sclerosis and systemic lupus erythematosus. Archives of Neurology, 46(10), 1121–1123.
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