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

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).

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.

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 R²≥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 R²≥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.

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.