Minimizing the Effect of IMU Misplacement With a Functional Orientation Method

Abstract

Background: Functional orientation orients inertial measurement unit (IMU) data (i.e., linear accelerations and angular velocities) to interpretable reference frames. To confidently collect reliable out-of-lab data, it is important to determine the extent to which we can correct for sensor placement variability. Research Question: To what extent does a functional orientation method minimize the effect of variability in sensor placement on IMU data? Methods: Twenty healthy adults (10 younger 28.2+/-3.7 years, 10 older 60.8+/-3.3years) walked overground at preferred speed in a lab. Three IMUs were placed per segment on the pelvis, thigh, shank, and foot. IMU data were oriented using an assumed orientation and two versions of a walking-based functional orientation (X-functional anchored to axis of rotation and Z-functional anchored to gravity). Segment angular excursions were calculated for each orientation method and compared between groups and sensor placements. Results and Significance: No significant interaction was found between sensor placement and group for any orientation method. For assumed orientation, segment angular excursion differed between sensor placements for at least 15% and up to 95% of the gait cycle, depending on segment. For both functional orientation methods, foot and shank excursions did not differ between sensors. Thigh excursion differed only for the X-functional orientation from 27-68% of the gait cycle. Neither functional orientation fully corrected for differences at the pelvis leaving significantly different excursions between 24-50% of the gait cycle. Functional orientation can reliably correct for variability in lower extremity IMU sensor placement. These methods can enable repeatable real-world IMU data collection in settings where sensors may move within or between days. Performing functional orientation periodically throughout a day can minimize the effect of sliding or rotating of the sensors on IMU-calculated gait measures and give in-lab quality gait data throughout hours of real-world activity to better understand the true movement of participants.

Competing Interest Statement

The authors have declared no competing interest.

Funding Statement

This study did not receive any funding

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IRB of University of Delaware gave ethical approval for this work.

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Data Availability

All data produced in the present study are available upon reasonable request to the authors

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