title: Physical Fatigue, Fitness, and Muscle Function in Patients With Antineutrophil Cytoplasmic Antibody-Associated Vasculitis.
abstract: This study investigated differences in cardiorespiratory fitness, muscular function, perceived exertion, and anxiety/depression between patients and healthy controls (HCs) and assessed which of these variables may account for the fatigue experienced by patients.
  
  
  
  Fatigue was measured in 48 antineutrophil cytoplasmic antibody-associated vasculitis patients and 41 healthy controls using the Multidimensional Fatigue Inventory (MFI-20), focusing on the physical component. Quality of life, anxiety/depression, and sleep quality were assessed by validated questionnaires. Muscle mass was measured by dual-energy x-ray absorptiometry scan, strength as the maximal voluntary contraction (MVC) force, and endurance as sustained isometric contraction at 50% MVC of the quadriceps. Voluntary activation was assessed by superimposed electrical stimulation. Cardiorespiratory fitness ( ˙Vo2 max and oxygen pulse [O2 pulse]) and perceived exertion (Borg scale) were measured during progressive submaximal exercise.
  
  
  
  Patients reported elevated physical fatigue scores compared to HCs (patients MFI-20 physical 13 [interquartile range (IQR) 8-16], HCs MFI-20 physical 5.5 [IQR 4-8]; P < 0.001). Muscle mass was the same in both groups, but MVC and time to failure in the endurance test were lower due to reduced voluntary activation in patients. Estimated ˙Vo2 max and O2 pulse were the same in both groups. For the same relative workload, patients reported higher ratings of perceived exertion, which correlated with reports of MFI-20 physical fatigue (R(2)  = 0.2). Depression (R(2)  = 0.6), anxiety (R(2)  = 0.3), and sleep disturbance (R(2)  = 0.3) were all correlated with MFI-20 physical fatigue.
  
  
  
  These observations suggest that fatigue in patients is of a central rather than peripheral origin, supported by associations of fatigue with heightened perception of exertion, depression, anxiety, and sleep disturbance but normal muscle and cardiorespiratory function.
authors.affiliation: Centre for Translational Inflammation Research, University of Birmingham, Birmingham, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: McClean
authors.affiliation: Centre for Translational Inflammation Research, University of Birmingham, Birmingham, UK.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Morgan
authors.affiliation: School of Medicine and Dentistry, University of Aberdeen, Aberdeen, UK.
authors.forename: Neil
authors.initials: N
authors.lastname: Basu
authors.affiliation: University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Jos A
authors.initials: JA
authors.lastname: Bosch
authors.affiliation: NIHR/Wellcome Trust Birmingham Clinical Research Facility, UHB NHS Foundation Trust, Birmingham, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Nightingale
authors.affiliation: School of Healthcare Science, Manchester Metropolitan University, Manchester, UK.
authors.forename: David
authors.initials: D
authors.lastname: Jones
authors.affiliation: Centre for Translational Inflammation Research, University of Birmingham, Birmingham, UK.
authors.forename: Lorraine
authors.initials: L
authors.lastname: Harper
mesh_terms: D000368:Aged; D056648:Anti-Neutrophil Cytoplasmic Antibody-Associated Vasculitis / Q000150:complications* / Q000503:physiopathology / Q000523:psychology; D001007:Anxiety / Q000209:etiology; D003863:Depression / Q000209:etiology; D005221:Fatigue / Q000209:etiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018763:Muscle Fatigue / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000503:physiopathology; D010809:Physical Fitness; D011788:Quality of Life; D011795:Surveys and Questionnaires