title: Can recovery of peripheral muscle function predict cognitive task performance in chronic fatigue syndrome with and without fibromyalgia?
abstract: BACKGROUND
  Both good physical and cognitive functioning have a positive influence on the execution of activities of daily living. Patients with chronic fatigue syndrome (CFS) as well as patients with fibromyalgia have marked cognitive deficits. Furthermore, a good physical and functional health status may have a positive impact on a variety of cognitive skills-a link that has been observed in young and old individuals who are healthy, although evidence is limited in patients with CFS.
  
  
  OBJECTIVE
  The purpose of this study was to examine whether recovery of upper limb muscle function could be a significant predictor of cognitive performance in patients with CFS and in patients with CFS and comorbid fibromyalgia. Furthermore, this study determined whether cognitive performance is different between these patient groups.
  
  
  METHODS
  A case-control design was used.
  
  
  METHODS
  Seventy-eight participants were included in the study: 18 patients with CFS only (CFS group), 30 patients with CFS and comorbid fibromyalgia (CFS+FM group), and 30 individuals who were healthy and inactive (control group) were studied. Participants first completed 3 performance-based cognitive tests designed to assess selective and sustained attention, cognitive inhibition, and working memory capacity. Seven days later, they performed a fatiguing upper limb exercise test, with subsequent recovery measures.
  
  
  RESULTS
  Recovery of upper limb muscle function was found to be a significant predictor of cognitive performance in patients with CFS. Participants in the CFS+FM group but not those in the CFS group showed significantly decreased cognitive performance compared with the control group.
  
  
  CONCLUSIONS
  The cross-sectional nature of this study does not allow for inferences of causation.
  
  
  CONCLUSIONS
  The results suggest that better physical health status could predict better mental health in patients with CFS. Furthermore, they underline disease heterogeneity, suggesting that reducing this factor in future research is important to better understand and uncover mechanisms regarding the nature of diverse impairments in these patients.
authors.affiliation: K. Ickmans, PT, MSc, Pain in Motion Research Group, Department of Human Physiology and Physiotherapy, Faculty of Physical Education and Physiotherapy, Vrije Universiteit Brussel, Brussels, Belgium; Pain in Motion Research Group, Division of Musculoskeletal Physiotherapy, Department of Health Care Sciences, Artesis University College, Antwerp, Belgium; and Pain in Motion Research Group, Department of Physical Medicine and Physiotherapy, University Hospital Brussels, Brussels, Belgium.
authors.forename: Kelly
authors.initials: K
authors.lastname: Ickmans
authors.forename: Mira
authors.initials: M
authors.lastname: Meeus
authors.forename: Margot
authors.initials: M
authors.lastname: De Kooning
authors.forename: Luc
authors.initials: L
authors.lastname: Lambrecht
authors.forename: Nathalie
authors.initials: N
authors.lastname: Pattyn
authors.forename: Jo
authors.initials: J
authors.lastname: Nijs
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D003071:Cognition / Q000502:physiology*; D003430:Cross-Sectional Studies; D015673:Fatigue Syndrome, Chronic / Q000503:physiopathology / Q000523:psychology*; D005260:Female; D005356:Fibromyalgia / Q000503:physiopathology / Q000523:psychology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology*; D011237:Predictive Value of Tests; D020127:Recovery of Function / Q000502:physiology*; D013647:Task Performance and Analysis; D055815:Young Adult