Schematic of the data processing pipeline.

Marker trajectories from optical motion capture and accelerations and rotations captured from the Notch IMU system (m_IMU) were recorded simultaneously during 5 activities of daily living. Tri-planar knee angles of were calculated using inverse kinematics analysis in OpenSim using marker trajectories (OMC) and from direct calculation from quaternions (r_IMU). Only sagittal plane knee angles were calculated for IMU system with embedded kinematic model (m_IMU) as depicted in the bottom right-hand plot.