title: Improvement in upper leg muscle strength underlies beneficial effects of exercise therapy in knee osteoarthritis: secondary analysis from a randomised controlled trial.
abstract: OBJECTIVE
  Although exercise therapy is effective for reducing pain and activity limitations in patients with knee osteoarthritis (OA), the underlying mechanisms are unclear. This study aimed to evaluate if improvements in neuromuscular factors (i.e. upper leg muscle strength and knee proprioception) underlie the beneficial effects of exercise therapy in patients with knee OA.
  
  
  METHODS
  Secondary analyses from a randomised controlled trial, with measurements at baseline, 6 weeks, 12 weeks and 38 weeks.
  
  
  METHODS
  Rehabilitation centre.
  
  
  METHODS
  One hundred and fifty-nine patients diagnosed with knee OA.
  
  
  METHODS
  Exercise therapy.
  
  
  METHODS
  Changes in pain [numeric rating scale (NRS)] and activity limitations [Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) physical function subscale and get-up-and-go test] during the study period. Independent variables were changes in upper leg muscle strength and knee joint proprioception (i.e. motion sense) during the study period. Longitudinal regression analyses (generalised estimating equation) were performed to analyse associations between changes in upper leg muscle strength and knee proprioception with changes in pain and activity limitations.
  
  
  RESULTS
  Improved muscle strength was significantly associated with reductions in NRS pain {B coefficient -2.5 [95% confidence interval (CI) -3.7 to -1.4], meaning that every change of 1 unit of strength was linked to a change of -2.5 units of pain}, WOMAC physical function (-8.8, 95% CI -13.4 to -4.2) and get-up-and-go test (-1.7, 95% CI -2.4 to -1.0). Improved proprioception was not significantly associated with better outcomes of exercise therapy (P>0.05).
  
  
  CONCLUSIONS
  Upper leg muscle strengthening is one of the mechanisms underlying the beneficial effects of exercise therapy in patients with knee OA.
authors.affiliation: Amsterdam Rehabilitation Research Centre, Reade, The Netherlands. Electronic address: jesperknoop@hotmail.com.
authors.forename: J
authors.initials: J
authors.lastname: Knoop
authors.affiliation: School of Health and Life Sciences, Institute for Applied Health Research, Glasgow Caledonian University, UK.
authors.forename: M P M
authors.initials: MP
authors.lastname: Steultjens
authors.affiliation: Amsterdam Rehabilitation Research Centre, Reade, The Netherlands.
authors.forename: L D
authors.initials: LD
authors.lastname: Roorda
authors.affiliation: Jan van Breemen Research Institute, Reade, The Netherlands; Department of Rheumatology, VU University Medical Centre, The Netherlands.
authors.forename: W F
authors.initials: WF
authors.lastname: Lems
authors.affiliation: Amsterdam Rehabilitation Research Centre, Reade, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: van der Esch
authors.affiliation: Department of Clinical Neuroscience and Physiology, University of Gothenburg, Sweden.
authors.forename: C A
authors.initials: CA
authors.lastname: Thorstensson
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, EMGO Institute, VU University Medical Centre, The Netherlands.
authors.forename: J W R
authors.initials: JW
authors.lastname: Twisk
authors.affiliation: Department of General Practice, Department of Orthopaedics, University Medical Centre Rotterdam, Erasmus MC, The Netherlands.
authors.forename: S M A
authors.initials: SM
authors.lastname: Bierma-Zeinstra
authors.affiliation: Amsterdam Rehabilitation Research Centre, Reade, The Netherlands; Department of Rehabilitation Medicine, EMGO Institute, VU University Medical Centre, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: van der Leeden
authors.affiliation: Department of Rehabilitation Medicine, EMGO Institute, VU University Medical Centre, The Netherlands; Department of Psychiatry, VU University Medical Centre, The Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: Dekker
mesh_terms: D000368:Aged; D005081:Exercise Therapy; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D007866:Leg; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal; D020370:Osteoarthritis, Knee / Q000534:rehabilitation*; D010146:Pain / Q000534:rehabilitation*; D026741:Physical Therapy Modalities; D011434:Proprioception; D012047:Rehabilitation Centers
keywords: Exercise therapy; Longitudinal analysis; Muscle strength; Neuromuscular mechanisms; Proprioception