Estimation of time-varying ankle joint stiffness under dynamic conditions via system identification techniques

Conference paper (2019)

Authors

Alejandro Moya Esteban University of Twente
Ronald C. Van 'T Veld University of Twente
Christopher P. Cop University of Twente
G. Durandau University of Twente
M. Sartori University of Twente
A.C. Schouten Biomechatronics & Human-Machine Control - Mechanical, Maritime and Materials Engineering , University of Twente
Research Group
Biomechatronics & Human-Machine Control (Mechanical, Maritime and Materials Engineering) (TU Delft)
Copyright: © 2019 Alejandro Moya Esteban, Ronald C. Van 'T Veld, Christopher P. Cop, Guillaume Durandau, Massimo Sartori, A.C. Schouten
DOI: https://doi.org/10.1109/EMBC.2019.8856423
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Published Date

2019

Language

English

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Faculty

Mechanical, Maritime and Materials Engineering

Department

Biomechanical Engineering

Research Group

Biomechatronics & Human-Machine Control

Abstract

An important goal in the design of next-generation exoskeletons and limb prostheses is to replicate human limb dynamics. Joint impedance determines the dynamic relation between joint displacement and torque. Joint stiffness is the position-dependent component of joint impedance and is key in postural control and movement. However, the mechanisms to modulate joint stiffness are not fully understood yet. The goal of this study is to conduct a systematic analysis on how humans modulate ankle stiffness. Time-varying stiffness was estimated for six healthy subjects under isometric, as well as quick and slow dynamic conditions via system identification techniques; specifically, an ensemble-based algorithm using short segments of ankle torque and position recordings. Our results show that stiffness had the lowest magnitude under quick dynamic conditions. Under isometric conditions, with fixed position and varying muscle activity, stiffness exhibited a higher magnitude. Finally, under slow dynamic conditions, stiffness was found to be the highest. Our results highlight, for the first time, the variability in stiffness modulation strategies across conditions, especially across movement velocity.