title: Model-Based Estimation of Ankle Joint Stiffness.
abstract: We address the estimation of biomechanical parameters with wearable measurement technologies. In particular, we focus on the estimation of sagittal plane ankle joint stiffness in dorsiflexion/plantar flexion. For this estimation, a novel nonlinear biomechanical model of the lower leg was formulated that is driven by electromyographic signals. The model incorporates a two-dimensional kinematic description in the sagittal plane for the calculation of muscle lever arms and torques. To reduce estimation errors due to model uncertainties, a filtering algorithm is necessary that employs segmental orientation sensor measurements. Because of the model's inherent nonlinearities and nonsmooth dynamics, a square-root cubature Kalman filter was developed. The performance of the novel estimation approach was evaluated in silico and in an experimental procedure. The experimental study was conducted with body-worn sensors and a test-bench that was specifically designed to obtain reference angle and torque measurements for a single joint. Results show that the filter is able to reconstruct joint angle positions, velocities and torque, as well as, joint stiffness during experimental test bench movements.
authors.affiliation: Philips Chair for Medical Information Technology, RWTH Aachen University, Pauwelsstrasse 20, 52074 Aachen, Germany. misgeld@hia.rwth-aachen.de.
authors.forename: Berno J E
authors.initials: BJ
authors.lastname: Misgeld
authors.affiliation: Philips Chair for Medical Information Technology, RWTH Aachen University, Pauwelsstrasse 20, 52074 Aachen, Germany. tony.zhang@rwth-aachen.de.
authors.forename: Tony
authors.initials: T
authors.lastname: Zhang
authors.affiliation: Philips Chair for Medical Information Technology, RWTH Aachen University, Pauwelsstrasse 20, 52074 Aachen, Germany. lueken@hia.rwth-aachen.de.
authors.forename: Markus J
authors.initials: MJ
authors.lastname: Lüken
authors.affiliation: Philips Chair for Medical Information Technology, RWTH Aachen University, Pauwelsstrasse 20, 52074 Aachen, Germany. leonhardt@hia.rwth-aachen.de.
authors.forename: Steffen
authors.initials: S
authors.lastname: Leonhardt
mesh_terms: D000843:Ankle Joint; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D006801:Humans; D009068:Movement; D019415:Torque
keywords: BSN; body-worn sensors; joint stiffness estimation; magnetic, angular rate and gravity sensors