Standardizing the analysis of physical activity in patients with COPD following a pulmonary rehabilitation program

Chest. 2014 Aug;146(2):318-327. doi: 10.1378/chest.13-1968.


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.

Trial registry:; No.: NCT00948623; URL:

Publication types

  • Multicenter Study
  • Randomized Controlled Trial

MeSH terms

  • Accelerometry
  • Activities of Daily Living*
  • Aged
  • Exercise Test
  • Exercise Therapy / methods*
  • Exercise Tolerance*
  • Female
  • Follow-Up Studies
  • Forced Expiratory Volume
  • Humans
  • Male
  • Motor Activity / physiology*
  • Prognosis
  • Pulmonary Disease, Chronic Obstructive / physiopathology
  • Pulmonary Disease, Chronic Obstructive / rehabilitation*
  • Vital Capacity

Associated data