title: Physical functioning: self-report and performance measures are related but distinct.
abstract: METHODS
  Cross-sectional study of 63 patients with chronic low back pain (CLBP).
  
  
  OBJECTIVE
  To determine the relationship between the SF-36 physical functioning (PF) scale and physical performance on a modified symptom limited treadmill test, and to determine the effect of disability status and SF-36 mental health (MH) scores on self-reported physical functioning and on physical performance.
  
  
  BACKGROUND
  Patients with CLBP report low levels of physical functioning. Because self-report measures are influenced by psychosocial factors, such as disability and low MH, a common recommendation is to supplement self-report with objective or physical performance testing. Little information exists regarding whether performance testing is also influenced by disability and low MH.
  
  
  METHODS
  Patients completed the SF-36 and performed a maximal, symptom-limited, modified treadmill test. Total walking time and heart rate on the treadmill were registered. The effects of disability and low MH on self-report and performance testing were calculated by unpaired Student's t-testing and effect size estimation.
  
  
  RESULTS
  A strong relationship between the PF scale of the SF-36 and treadmill walking time was found, but there was little evidence of overlap between these physical functioning domains. Both disability status and low MH had a much larger effect on self-report measures than on physical performance.
  
  
  CONCLUSIONS
  Self-report measurements and performance-based assessments provide information about distinct, although related, domains of physical functioning. Disability and low MH are associated with lower SF-36 PF scores. Our results confirm that self-report measures require supplementation with objective performance testing to provide optimal assessment for patients with CLBP.
authors.affiliation: Department of Physical Therapy, VU Medical Center, De Boelelaan, Amsterdam.
authors.forename: Harriët
authors.initials: H
authors.lastname: Wittink
authors.forename: William
authors.initials: W
authors.lastname: Rogers
authors.forename: Andrew
authors.initials: A
authors.lastname: Sukiennik
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Carr
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D002908:Chronic Disease; D003430:Cross-Sectional Studies; D004185:Disability Evaluation; D005080:Exercise Test; D005260:Female; D006339:Heart Rate; D006801:Humans; D017116:Low Back Pain / Q000503:physiopathology* / Q000523:psychology; D008297:Male; D008603:Mental Health; D008875:Middle Aged; D011788:Quality of Life; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires