Assessment of sedentary behaviour in individuals with COPD: how many days are necessary?

Objective The objective of the present study was to define the minimum number of monitoring days required for the adequate cross-sectional assessment of sedentary behaviour in individuals with chronic obstructive pulmonary disease (COPD). Methods In this cross-sectional study, the sedentary behaviour of individuals with COPD was assessed using two physical activity monitors during awake time for seven consecutive days. Time spent per day in activities requiring <= 1.5 metabolic equivalents (METs) and in sitting, lying and sitting+lying positions was calculated taking into account the average of 7 days (as a reference in all analyses) and of all 119 possible combinations of 2-6 days. Intraclass correlation coefficients (ICCs) and linear regression analyses were performed for all combinations. Results 91 individuals were analysed (47 female, 66 +/- 9 years, forced expiratory volume in 1 s 50 +/- 15% predicted). For the variables time spent per day in activities <= 1.5METs and sitting, the average of any combination of at least four assessment days was sufficient to adequately reflect the average of 7 days (adjusted R-2 >= 0.929, ICC >= 0.962, p<0.0001 for all). For time spent per day lying and sitting+lying, only two assessment days were enough (adjusted R-2 >= 0.937, ICC >= 0.968, p<0.0001 for all). Results were maintained independently of patient sex, disease severity, day of the week, daylight time or daytime naps. Conclusions The average of 4 days of objective monitoring was sufficient to adequately reflect the results of a 1-week assessment of the main outcomes related to sedentary behaviour in individuals with moderate to very severe COPD, regardless of sex, disease severity, day of the week, daylight time and occurrence of daytime naps.

Automated summary

The objective of this study was to determine the minimum number of monitoring days required for accurate assessment of sedentary behavior in individuals with COPD. The results showed that at least four assessment days were sufficient to reflect the average of seven days for variables such as time spent in activities requiring <= 1.5METs and sitting, while only two assessment days were enough for time spent lying and sitting+lying.