title: Capturing the post-exertional exacerbation of fatigue following physical and cognitive challenge in patients with chronic fatigue syndrome.
abstract: OBJECTIVE
  To design and validate an instrument to capture the characteristic post-exertional exacerbation of fatigue in patients with chronic fatigue syndrome (CFS).
  
  
  METHODS
  Firstly, patients with CFS (N=19) participated in five focus group discussions to jointly explore the nature of fatigue and dynamic changes after activity, and inform development of a self-report instrument - the Fatigue and Energy Scale (FES). The psychometric properties of the FES were then examined in two case-control challenge studies: a physically-demanding challenge (moderate-intensity aerobic exercise; N=10 patients), and a cognitively-demanding challenge (simulated driving; N=11 patients). Finally, ecological validity was evaluated by recording in association with tasks of daily living (N=9).
  
  
  RESULTS
  Common descriptors for fatigue included 'exhaustion', 'tiredness', 'drained of energy', 'heaviness in the limbs', and 'foggy in the head'. Based on the qualitative data, fatigue was conceptualised as consisting of 'physical' and 'cognitive' dimensions. Analysis of the psychometric properties of the FES showed good sensitivity to the changing symptoms during a post-exertional exacerbation of fatigue following both physical exercise and driving simulation challenges, as well as tasks of daily living.
  
  
  CONCLUSIONS
  The 'fatigue' experienced by patients with CFS covers both physical and cognitive components. The FES captured the phenomenon of a post-exertional exacerbation of fatigue commonly reported by patients with CFS. The characteristics of the symptom response to physical and cognitive challenges were similar. Both the FES and the challenge paradigms offer key tools to reliably investigate biological correlates of the dynamic changes in fatigue.
authors.affiliation: School of Medical Sciences, University of New South Wales, Sydney, Australia. Electronic address: andrew.keech@unsw.edu.au.
authors.forename: Andrew
authors.initials: A
authors.lastname: Keech
authors.affiliation: School of Medical Sciences, University of New South Wales, Sydney, Australia.
authors.forename: Carolina X
authors.initials: CX
authors.lastname: Sandler
authors.affiliation: School of Psychiatry, University of New South Wales, Sydney, Australia.
authors.forename: Ute
authors.initials: U
authors.lastname: Vollmer-Conna
authors.affiliation: School of Psychiatry, University of New South Wales, Sydney, Australia.
authors.forename: Erin
authors.initials: E
authors.lastname: Cvejic
authors.affiliation: Inflammation and Infection Research Centre, School of Medical Sciences, University of New South Wales, Sydney, Australia.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Lloyd
authors.affiliation: School of Medical Sciences, University of New South Wales, Sydney, Australia; Neuroscience Research Australia, Sydney, Australia.
authors.forename: Benjamin K
authors.initials: BK
authors.lastname: Barry
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D016022:Case-Control Studies; D003071:Cognition / Q000502:physiology*; D004734:Energy Metabolism; D015444:Exercise; D005221:Fatigue / Q000523:psychology*; D015673:Fatigue Syndrome, Chronic / Q000523:psychology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D005082:Physical Exertion; D011594:Psychometrics; D011795:Surveys and Questionnaires
keywords: Myalgic encephalomyelitis; Perceived exertion; Post-exertional malaise; Questionnaire; Systemic exertion intolerance disease