How Many Days Do We Need? Defining Reliable ActivPAL Monitoring Protocols for Distinct Movement Behaviors in Office Workers.

Although device-measured data provide more reliable estimates of movement behaviors than self-report questionnaires, device-monitoring protocols are often demanding in terms of time, logistics, and costs. Identifying the minimum monitoring duration to obtain reliable data is therefore essential, yet evidence for ActivPAL devices remains limited. The objective of this study was to determine the minimum number of days required to reliably estimate movement behaviors using ActivPAL. As a secondary aim, we examined how different combinations of weekdays and weekend days influence reliability. A total of 106 monitoring periods of six consecutive days from adult office workers were analyzed, corresponding to 636 monitored days or 15 264 h collected. Taking the 6-day period as reference, the reliability of shorter monitoring durations (1-5 days) was assessed. Relative and absolute reliability were confirmed when an intraclass correlation coefficient ≥ 0.85 and a coefficient of variation < 10% were achieved, respectively. Movement behaviors assessed included stepping time, standing time, sedentary time, sitting time, primary lying time, step count, and sit-to-stand transitions. Based on these criteria, two monitoring days were sufficient to achieve both relative and absolute reliability for sit-to-stand transitions, while 3 days were sufficient for sedentary time, sitting time, and primary lying time. Four days were required to achieve comparable reliability for stepping time, standing time, and step count. Overall, monitoring periods that combined weekdays and weekend days tended to demonstrate higher reliability than those including only weekdays or weekend days. These findings may guide optimization of ActivPAL monitoring protocols, reducing participant and researcher burden while maintaining reliable movement behavior estimates.