title: Can we explain heterogeneity among randomized clinical trials of exercise for chronic back pain? A meta-regression analysis of randomized controlled trials.
abstract: BACKGROUND
  Exercise programs may vary in terms of duration, frequency, and dosage; whether they are supervised; and whether they include a home-based program. Uncritical pooling of heterogeneous exercise trials may result in misleading conclusions regarding the effects of exercise on chronic low back pain (CLBP).
  
  
  OBJECTIVE
  The purpose of this study was to establish the effect of exercise on pain and disability in patients with CLBP, with a major aim of explaining between-trial heterogeneity.
  
  
  METHODS
  Six databases were searched up to August 2008 using a computerized search strategy.
  
  
  METHODS
  Eligible studies needed to be randomized clinical trials evaluating the effects of exercise for nonspecific CLBP. Outcomes of interest were pain and disability measured on a continuous scale.
  
  
  METHODS
  Baseline demographic data, exercise features, and outcome data were extracted from all included trials.
  
  
  RESULTS
  Univariate meta-regressions were conducted to assess the associations between exercise effect sizes and 8 study-level variables: baseline severity of symptoms, number of exercise hours and sessions, supervision, individual tailoring, cognitive-behavioral component, intention-to-treat analysis, and concealment of allocation.
  
  
  CONCLUSIONS
  Only study-level characteristics were included in the meta-regression analyses. Therefore, the implications of the findings should not be used to differentiate the likelihood of the effect of exercise based on patient characteristics.
  
  
  CONCLUSIONS
  The results show that, in general, when all types of exercise are analyzed, small but significant reductions in pain and disability are observed compared with minimal care or no treatment. Despite many possible sources of heterogeneity in exercise trials, only dosage was found to be significantly associated with effect sizes.
authors.affiliation: Faculty of Health Sciences, University of Sydney, 75 East St, PO Box 170, Lidcombe, New South Wales 1825, Australia. manuela.ferreira@sydney.edu.au
authors.forename: Manuela L
authors.initials: ML
authors.lastname: Ferreira
authors.forename: Rob J E M
authors.initials: RJ
authors.lastname: Smeets
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Kamper
authors.forename: Paulo H
authors.initials: PH
authors.lastname: Ferreira
authors.forename: Luciana A C
authors.initials: LA
authors.lastname: Machado
mesh_terms: D002908:Chronic Disease; D005081:Exercise Therapy / Q000379:methods*; D006801:Humans; D017116:Low Back Pain / Q000503:physiopathology / Q000534:rehabilitation*; D016032:Randomized Controlled Trials as Topic; D012044:Regression Analysis; D016896:Treatment Outcome