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People with chronic obstructive pulmonary disease (COPD) have reduced physical activity (PA) levels compared with healthy controls. The pattern of their PA level during the day is much less documented. A better understanding of these diurnal PA patterns could help optimize interventions targeting PA levels in this population. The aim of this study was to examine, in patients with COPD, diurnal PA patterns using accelerometer data and different approaches to data handling (arbitrary, mealtime, equal tertiles).Fourteen COPD patients (aged 71 ± 9 yr; forced expiratory volume in 1 sec [FEV1]: 58% ± 13% predicted) completed the study. Daily PA was assessed via accelerometry for 7 d, 24 hr/d. Diurnal PA patterns were evaluated using an arbitrary (08:00-12:00, 12:01-16:00, 16:01-20:00), mealtime (wake time-lunchtime, lunchtime-suppertime, suppertime-bedtime), and equal tertiles (tertiles 1, 2, and 3) approaches. Results were interpreted on the basis of descriptive statistics and effect sizes (Cohen f) for time-of-day changes in PA.Regardless of the handling approach used, mean PA levels decreased in the evening and the effect size for time-of-day changes in PA level was large (f = 0.97; 1.82; and 1.66 for the arbitrary, mealtimes, and tertiles approaches, respectively). The observation of a decrease in the evening was highly homogeneous across our sample, particularly with the mealtime and equal tertiles handling approach.Results from this study support prior findings that PA levels decrease substantially in the evening in patients with COPD, thereby providing a better understanding of within-day PA behavior and offering valuable insight into interventions targeting PA.