Standardizing the Analysis of Physical Activity in Patients With COPD Following a Pulmonary Rehabilitation Program

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 aft er pulmonary rehabilitation. METHODS: Physical activity was measured with an activity monitor armband in 57 patients with COPD (mean +/- SD age, 66 +/- 7 years; FEV 1, 46 +/- 17% predicted) before and aft er 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, post-processing 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.