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 R2≥0.929, ICC≥0.962, p