The relationship between electrical stimulus and joint torque: a dynamic model

The knowledge of the behavior of electrically activated muscles is an important requisite for the development of functional electrical stimulation (FES) systems to restore mobility to persons with paralysis. The aim of this work was to develop a model capable of relating electrical parameters to dyn...

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Bibliographic Details
Published in:IEEE transactions on neural systems and rehabilitation engineering 2000-09, Vol.8 (3), p.342-352
Main Authors: Ferrarin, M., Pedotti, A.
Format: Article
Language:English
Subjects:
Bias
Biomechanics
Case-Control Studies
Damping
Elasticity
Electric Stimulation Therapy - methods
Electrodes
Electrophysiology
Gravitation
Humans
Joints
Joints (anatomy)
Knee
Knee Joint - physiopathology
Leg
Leg - physiopathology
Male
Models, Biological
Muscle Contraction - physiology
Muscles
Musculoskeletal system
Neuromuscular stimulation
Nonlinear dynamical systems
Nonlinear Dynamics
Paraplegia - physiopathology
Paraplegia - rehabilitation
Physiological models
Range of Motion, Articular - physiology
Stiffness
Testing
Time Factors
Torque
Viscosity
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Summary:The knowledge of the behavior of electrically activated muscles is an important requisite for the development of functional electrical stimulation (FES) systems to restore mobility to persons with paralysis. The aim of this work was to develop a model capable of relating electrical parameters to dynamic joint torque for FES applications. The knee extensor muscles, stimulated using surface electrodes, were used for the experimental preparation. Both healthy subjects and people with paraplegia were tested. The dynamics of the lower limb were represented by a nonlinear second order model, which took account of the gravitational and inertial characteristics of the anatomical segments as well as the damping and stiffness properties of the knee joint. The viscous-elastic parameters of the system were identified experimentally through free pendular movements of the leg. Leg movements induced by quadriceps stimulation were acquired too, using a motion analysis system. Results showed that, for the considered experimental conditions, a simple one-pole transfer function is able to model the relationship between stimulus pulsewidth (PW) and active muscle torque. The time constant of the pole was found to depend on the stimulus pattern (ramp or step) while gain was directly dependent on stimulation frequency.
ISSN:1063-6528
1534-4320
1558-0024
1558-0210
DOI:10.1109/86.867876