A Functional Sensor-to-Segment Calibration Method Reduces the Effects of Varied Sensor Placement on Estimates of Segment Angular Excursion

To collect reliable data, it is important to determine how inertial measurement unit (IMU) sensor placement affects measurements of segment motion. We aimed to determine the extent to which a functional sensor-to-segment calibration method minimizes the effect of variations in sensor placement on IMU-derived segment angular excursions. Twenty healthy adults walked while wearing 3 IMUs placed on each of the pelvis, thigh, shank, and foot. Differences in estimated segment angular excursions between sensor placements were compared between an assumed sensor-to-segment calibration and 2 versions of a walking-based functional sensor-to-segment calibration. The performance of the functional calibration methods varied. The shank had the greatest difference in root mean square difference between methods (15° for assumed, 1.5° for functional calibration), but the pelvis and thigh did not have significant differences in root mean square difference between assumed and functional calibrations. Mean root mean square differences for angular excursion between sensors were <5° for most comparisons for assumed and functional calibrations. Functional calibration reduced between-subject variance in intersensor differences for all segments. Functional calibration can minimize the effect of variations in IMU sensor placement, but care should be taken to select sensor placements that minimize soft-tissue artifact (eg, anterior thigh).