Validity and sensitivity of an inertial measurement unit-driven biomechanical model of motor variability for gait

Motor variability in gait is frequently linked to fall risk, yet field-based biomechanical joint evaluations are scarce. We evaluated the validity and sensitivity of an inertial measurement unit (IMU)-driven biomechanical model of joint angle variability for gait. Fourteen healthy young adults completed seven-minute trials of treadmill gait at several speeds and arm swing amplitudes. Joint kinematics were estimated by IMU- and optoelectronic-based models using OpenSim. We calculated range of motion (ROM), magnitude of variability (meanSD), local dynamic stability ({lambda}max), persistence of ROM fluctuations (DFA), and regularity (SaEn) of each angle over 200 continuous strides, and evaluated model accuracy (e.g., RMSD: root mean square difference), consistency (ICC2,1: intraclass correlation), biases, limits of agreement, and sensitivity to within-participant gait responses (effects of Speed and Swing). RMSDs of joint angles were 1.7-7.5{degrees} (pooled mean of 4.8{degrees}), excluding ankle inversion. ICCs were mostly good- excellent in the primary plane of motion for ROM and in all planes for meanSD and {lambda}max, but were poor-moderate for DFA and SaEn. Modeled Speed and Swing responses for ROM, meanSD, and {lambda}max were similar. Results suggest that the IMU-driven model is valid and sensitive for field-based assessments of joint angles and several motor variability features.