Reliability of 24-hours measurement of physical activity, sleep and sedentary time in adult patients with asthma using a triaxial accelerometer

Physical activity (PA), sleep and sedentary time (SST) are important outcomes to monitor and to improve as part of patients' asthma management. This study aimed to assess the number of measurement days needed to reliably measure PA and SST. Secondly, the influence of external factors on the reliability of measuring PA and SST was studied.Adult patients with stable asthma were asked to wear a triaxial accelerometer for at least four days, with at least 22.5 hours of wear time per day. The Intraclass Correlation Coefficients (ICCs) between different number of measurement days were used to determine reliability. Values =0.75 indicated good reliability. Data from 452 patients were analyzed (63% women; age: 49 ± 16 years; FEV : 87 ± 17% predicted). PA could reliably be measured with four valid measurement days, (ICC 0.761). For SST, three days were needed (ICC 0.778). In summer and autumn three days were needed to reliably measure PA, in winter four, in spring six. For SST, five days were needed in spring for good reliability, and two in all other seasons.Based on data from four valid days, PA and SST can reliably be measured with an accelerometer in patients with asthma. Seasonal influences are present, especially during spring. When measuring for four days, using only weekdays or three weekdays and one weekend day is recommended. The degree of asthma control, dyspnea or spirometric values did not influence the reliability.