A Novel Complimentary Filter for Tracking Hip Angles During Cycling Using Wireless Inertial Sensors and Dynamic Acceleration Estimation

As wireless motion sensors become more compact and robust, new opportunities emerge to develop wearable measurement technologies for in-field sports analysis. This paper presents a nonlinear complimentary filter for tracking 3-D hip joint angles during cycling using inertial and magnetic measurement systems (IMMSs). The filter utilizes a novel method of dynamic acceleration compensation in the sensor frame based on the assumption of pendulum motion of the thigh around the hip joint center. A dynamic calibration is proposed in which the center of rotation of the thigh IMMS can be estimated during a functional hip movement in standing. Validation results from a gold-standard optical system showed that the filter IMMS tracking is drift-free with mean absolute errors of less than 3° for all IMMS axes combined at low, medium, and high pedaling speeds. Hip angles were also validated using the Vicon biomechanical model for standing and sitting calibration poses as well as true and normalized soft-tissue-artefact (STA). The best mean absolute errors for the sagittal, frontal, and coronal planes were 0.8°, 6.7°, and 2.2°, respectively. Variability due to calibrations and STA ranged from 1.4° to 8.1°. This demonstrates the high accuracies possible for IMMS tracking using algorithms designed for specific sports despite larger errors due to modeling.