Accelerometer- versus questionnaire-based assessment of physical activity and their changes over time in patients with COPD

BACKGROUND AND OBJECTIVE Physical activity (PA) is an important outcome parameter in patients with COPD regarding hospitalizations and mortality. Both objective assessment by accelerometers and self-evaluation by questionnaires were used in studies investigating PA in COPD. Whether self-reported questionnaires can adequately reflect PA and its changes over time compared to objective assessments has not been thoroughly investigated in COPD. In this COPD cohort study, we evaluated whether PA measured by accelerometer and its annual changes can also be assessed by self-reported questionnaires. METHODS In 178 COPD patients with at least two assessments of PA, the agreement between objectively measured and self-reported activity was analyzed by Bland-Altman plots. Daily PA was assessed by a triaxial activity monitor over 1 week and by the self-reported German PA questionnaire 50+. RESULTS Comparison between the two methods of measurement revealed no convincing agreement with a mean difference and limits of agreement (±1.96 standard deviation [SD]) of time spent in at least moderate PA (>3 metabolic equivalent of task [MET]) of -77.6 (-340.3/185.2) min/day, indicating a self-reported overestimation of PA by the questionnaire. The mean difference and limits of agreement (±1.96SD) in the annual change of PA was 1.2 min/day (-208.2/282.6 min/day), showing also a poor agreement on an individual level. CONCLUSION Evaluation of objectively measured and self-reported PA and their annual changes revealed no agreement in patients with COPD. Therefore, the evaluated questionnaire seems not helpful for measurement of PA and its changes over time.