title: Standardizing the analysis of physical activity in patients with COPD following a pulmonary rehabilitation program.
abstract: BACKGROUND
  There is a wide variability in measurement methodology of physical activity. This study investigated the effect of different analysis techniques on the statistical power of physical activity outcomes after pulmonary rehabilitation.
  
  
  METHODS
  Physical activity was measured with an activity monitor armband in 57 patients with COPD (mean ± SD age, 66 ± 7 years; FEV1, 46 ± 17% predicted) before and after 3 months of pulmonary rehabilitation. The choice of the outcome (daily number of steps [STEPS], time spent in at least moderate physical activity [TMA], mean metabolic equivalents of task level [METS], and activity time [ACT]), impact of weekends, number of days of assessment, postprocessing techniques, and influence of duration of daylight time (DT) on the sample size to achieve a power of 0.8 were investigated.
  
  
  RESULTS
  The STEPS and ACT (1.6-2.3 metabolic equivalents of task) were the most sensitive outcomes. Excluding weekends decreased the sample size for STEPS (83 vs 56), TMA (160 vs 148), and METS (251 vs 207). Using 4 weekdays (STEPS and TMA) or 5 weekdays (METS) rendered the lowest sample size. Excluding days with < 8 h wearing time reduced the sample size for STEPS (56 vs 51). Differences in DT were an important confounder.
  
  
  CONCLUSIONS
  Changes in physical activity following pulmonary rehabilitation are best measured for 4 weekdays, including only days with at least 8 h of wearing time (during waking hours) and considering the difference in DT as a covariate in the analysis.
  
  
  BACKGROUND
  ClinicalTrials.gov; No.: NCT00948623; URL: www.clinicaltrials.gov.
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium; Respiratory Rehabilitation and Respiratory Division, University Hospital Leuven, Leuven, Belgium.
authors.forename: Heleen
authors.initials: H
authors.lastname: Demeyer
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium; Respiratory Rehabilitation and Respiratory Division, University Hospital Leuven, Leuven, Belgium; Department of Allied Health Professions, Fontys University of Applied Sciences, Eindhoven, The Netherlands.
authors.forename: Chris
authors.initials: C
authors.lastname: Burtin
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium; Respiratory Rehabilitation and Respiratory Division, University Hospital Leuven, Leuven, Belgium.
authors.forename: Hans
authors.initials: H
authors.lastname: Van Remoortel
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium; Respiratory Rehabilitation and Respiratory Division, University Hospital Leuven, Leuven, Belgium.
authors.forename: Miek
authors.initials: M
authors.lastname: Hornikx
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium; Respiratory Rehabilitation and Respiratory Division, University Hospital Leuven, Leuven, Belgium.
authors.forename: Daniel
authors.initials: D
authors.lastname: Langer
authors.affiliation: Respiratory Rehabilitation and Respiratory Division, University Hospital Leuven, Leuven, Belgium.
authors.forename: Marc
authors.initials: M
authors.lastname: Decramer
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium; Respiratory Rehabilitation and Respiratory Division, University Hospital Leuven, Leuven, Belgium.
authors.forename: Rik
authors.initials: R
authors.lastname: Gosselink
authors.affiliation: Respiratory Rehabilitation and Respiratory Division, University Hospital Leuven, Leuven, Belgium.
authors.forename: Wim
authors.initials: W
authors.lastname: Janssens
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium; Respiratory Rehabilitation and Respiratory Division, University Hospital Leuven, Leuven, Belgium. Electronic address: thierry.troosters@med.kuleuven.be.
authors.forename: Thierry
authors.initials: T
authors.lastname: Troosters
mesh_terms: D061725:Accelerometry; D000203:Activities of Daily Living; D000368:Aged; D005080:Exercise Test; D005081:Exercise Therapy / Q000379:methods*; D017079:Exercise Tolerance; D005260:Female; D005500:Follow-Up Studies; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D011379:Prognosis; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology / Q000534:rehabilitation*; D014797:Vital Capacity