Evaluation of Wearable Sensor Placement for Movement Bout Duration Estimation: A Comparative Feasibility Study

Wearable sensor placement can influence movement quantification, yet direct comparisons across anatomical sites remain limited for bout-level temporal outcomes. This study evaluated seven IMU placements for movement bout duration estimation. Twenty-seven healthy adults performed three whole-body tasks (walking, Timed Up and Go, and Step Test) and two upper-limb tasks (reaching and hand-to-mouth) under concurrent optoelectronic motion capture. IMU-derived durations were compared with segment-specific local references and, for whole-body tasks, a common sacral reference used as a proxy for whole-body movement. Agreement was assessed using Spearman's correlation, ICC, Bland-Altman analysis, and MAPE. Participant-level agreement analyses were complemented by trial-level repeated-measures analyses to account for within-participant variability across repeated trials. A descriptive composite ranking combined ICC, MAPE, and limits-of-agreement width against the common reference. Performance varied across placements and tasks, with the largest local-common dissociation observed during the TUG. The sacrum obtained the most favorable overall composite ranking score (2.78), closely followed by the dominant ankle (2.89) and non-dominant wrist (3.11). Both wrists showed high agreement during upper-limb tasks (ICC = 0.879-0.994). Trial-level analyses confirmed a significant effect of sensor placement for all whole-body tasks, while no significant differences were observed between wrist placements during the isolated upper-limb tasks. The non-dominant wrist showed a favorable combination of performance across movement domains, supporting its selection as a promising candidate for further evaluation in subsequent free-living monitoring.