title: Is quadriceps endurance reduced in COPD?: a systematic review.
abstract: BACKGROUND
  Although the aerobic profile of the quadriceps muscle is reduced in COPD, there is conflicting evidence regarding whether this leads to reduced quadriceps muscle endurance. We, therefore, performed a systematic review of studies comparing quadriceps endurance in individuals with COPD with that in healthy control subjects.
  
  
  METHODS
  Relevant studies were identified by searching six electronic databases (1946-2011). Full-text articles were obtained after two researchers independently reviewed the abstracts. The results were combined in a random effects meta-analysis, and metaregression models were fitted to assess the influence of the type of measurement.
  
  
  RESULTS
  Data were extracted from 21 studies involving 728 individuals with COPD and 440 healthy control subjects. Quadriceps endurance was reduced in those with COPD compared with healthy control subjects (standardized mean difference, 1.16 [95% CI, 1.02-1.30]; P < .001) with a 44.5 s (4.5-84.5 s; P = .029) reduction in COPD (large effect size) when measured using a nonvolitional technique. The relationship between quadriceps endurance in those with COPD and control subjects did not differ when comparing nonvolitional and volitional techniques (P = .22) or when high- or low-intensity tasks (P = .44) were undertaken.
  
  
  CONCLUSIONS
  Quadriceps endurance is reduced in individuals with COPD compared with healthy control subjects, independent of the type of task performed.
authors.affiliation: Department of Respiratory Medicine, Department of Medicine, University of Toronto, Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, England. Electronic address: rachael.evans@uhl-tr.nhs.uk.
authors.forename: Rachael A
authors.initials: RA
authors.lastname: Evans
authors.affiliation: Department of Respiratory Medicine, Department of Medicine, University of Toronto, Toronto, ON, Canada.
authors.forename: Eric
authors.initials: E
authors.lastname: Kaplovitch
authors.affiliation: Department of Respiratory Medicine, Department of Physical Therapy, Department of Physical Medicine and Rehabilitation, Harvard Medical School, Spaulding Rehabilitation Hospital, Cambridge, MA.
authors.forename: Marla K
authors.initials: MK
authors.lastname: Beauchamp
authors.affiliation: Department of Respiratory Medicine, West Park Healthcare Centre, Toronto, ON, Canada.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Dolmage
authors.affiliation: Department of Respiratory Medicine, Department of Medicine, University of Toronto, Toronto, ON, Canada.
authors.forename: Roger S
authors.initials: RS
authors.lastname: Goldstein
authors.affiliation: Department of Health Sciences, University of Leicester, Leicester, England.
authors.forename: Clare L
authors.initials: CL
authors.lastname: Gillies
authors.affiliation: Department of Respiratory Medicine, Department of Physical Therapy, University of Toronto, Toronto, ON, Canada.
authors.forename: Dina
authors.initials: D
authors.lastname: Brooks
authors.affiliation: Department of Respiratory Medicine, Department of Physical Therapy, University of Toronto, Toronto, ON, Canada.
authors.forename: Sunita
authors.initials: S
authors.lastname: Mathur
mesh_terms: D000368:Aged; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018763:Muscle Fatigue / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D052097:Quadriceps Muscle / Q000503:physiopathology*; D012720:Severity of Illness Index