Estimating tibial bone load during running using only inertial measurement units on the tibias and sternum: a Centre of Pressure approach

Inverse dynamics is a method to estimate joint forces and external moments needed for movement by analysing kinematics and ground reaction forces (GRF). In a bottom-up inverse dynamics analysis using a full-body inertial measurement unit (IMU) setup, the Centre of Pressure (CoP) is the only missing variable to complete the calculation. This study aimed to estimate the anteroposterior CoP from the tibia IMU orientation to calculate the sagittal ankle moment and tibial bone load (TBL) in rearfoot strikers running at 2.5, 3.1, and 3.6 m/s, using both tibia and the sternum IMU. This achieved strong correlations (≥0.90) for the CoP, sagittal ankle moment, and TBL compared with a marker/force plate reference. While the CoP estimate had fair accuracy, the sagittal ankle moment (rRMSE ≤ 12.9 %) and TBL (rRMSE ≤ 10.2 %) showed high accuracy. No significant differences were found between the IMU-only method and the reference for maximum ankle plantar flexion moment and TBL across all speeds. Future work should explore the multidimensional CoP, the inclusion of 3D GRF, and validation for non-rearfoot strike runners. These findings highlight the potential of using both tibia and the sternum IMU to monitor lower extremity forces and moments during running, independent of measurement location.