Estimation of Time-Varying Ankle Joint Stiffness Under Dynamic Conditions via System Identification Techniques

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 postura...

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Published in:Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual International Conference Vol. 2019; pp. 2119 - 2122
Main Authors: Esteban, Alejandro Moya, van 't Veld, Ronald C., Cop, Christopher P., Durandau, Guillaume, Sartori, Massimo, Schouten, Alfred C.
Format: Conference Proceeding Journal Article
Language:English
Published: United States IEEE 01.07.2019
Subjects:
Adult
Ankle Joint - physiology
Biomechanical Phenomena
Electromyography
Female
Healthy Volunteers
Humans
Impedance
Male
Movement
Muscle, Skeletal - physiology
Muscles
Perturbation methods
Postural Balance
Torque
Young Adult
ISSN:1557-170X, 2694-0604, 1558-4615, 2694-0604
Online Access:Get full text
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Summary: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.
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ISSN:1557-170X
2694-0604
1558-4615
2694-0604
DOI:10.1109/EMBC.2019.8856423