Accurate and repeatable sensor-to-body calibration of inertial measurement units for lower limbs motion analysis

Inertial Measurement Units (IMUs) became extremely popular for human motion analysis in the free-living environment thanks to their small size, lightweight, and long battery life [1,2]. However, IMU measures the acceleration and angular velocity in its sensor-fixed frame (SF), not the anatomical frame (AF) of the segment, to which it is attached. Thus, a sensor-to-body transformation (calibration) is required to obtain clinically meaningful joint kinematics. To this end, this paper presents an effortless calibration for aligning IMUs attached to the pelvis, thigh, shank, and foot. The accuracy and repeatability of the proposed calibration were validated through an experimental study with ten ablebodied participants.