Chest
Volume 146, Issue 2, August 2014, Pages 318-327
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Original Research
COPD
Standardizing the Analysis of Physical Activity in Patients With COPD Following a Pulmonary Rehabilitation Program

https://doi.org/10.1378/chest.13-1968Get rights and content
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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

ClinicalTrials.gov; No.: NCT00948623; URL: www.clinicaltrials.gov

Abbreviations

DT
duration of daylight time
ICC
intraclass correlation coefficient
METs
metabolic equivalents of task
METS
mean metabolic equivalents of task level
STEPS
daily number of steps
TMA
time spent in at least moderate physical activity

Cited by (0)

FUNDING/SUPPORT: This work was supported by the Flemish Research Foundation [Grant G.0871.13] and PROactive Innovative Medicines Initiative Joint Undertaking [Grant IMI-JU 115011]. Drs Langer and Janssens are postdoctoral research fellows of the Flemish Research Foundation.

Part of this article has been presented in abstract form at the American Thoracic Society 2012 International Conference, May 18-23, 2012, San Francisco, CA.

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