Characterization and control of muscle response to electrical stimulation |
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Authors: | T J Bajzek R J Jaeger PhD |
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Institution: | (1) Pritzker Institute of Medical Engineering, Illinois Institute of Technology, IIT Center, 60616 Chicago, IL;(2) Department of Surgery, Section of Orthopaedics Pritzker School of Medicine, The University of Chicago, 60616 Chicago, IL |
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Abstract: | The maintenance of upright posture in neurologically intact human subjects is mediated by two major nervous pathways. The
first, leading from the cerebral cortex through the spinal cord to motor neurons, activates muscles which produce postural
movements. The second, leading from various sensory organs to higher centers, provides sensory feedback regarding the postural
state. The path through the spinal cord is no longer intact in victims of spinal cord injury and loss of normal control of
muscle activity results. Functional neuromuscular stimulation (FNS) has been shown as a feasible method for obtaining muscle
contraction in paraplegic and has been proposed as a means for control of antero-posterior sway to make upright posture possible
for these individuals. Before muscle can be controlled through the use of FNS, the response of muscle to electrical stimulation
must be understood. In past studies, linear control theory has been applied to the analysis of this response and to the testing
of various controllers. The aim of this study was to demonstrate some control issues in FNS using linear control theory, as
it applies to electrical stimulation of muscle for stabilization of posture. The linearity of the muscle response was improved
through closed-loop control using pole compensation techniques. The excess phase shift of the system due to the time delay
in the muscle response, however, limits the ability to increase the open-loop gain in order to obtain improved performance.
A suggestion for further study is the application of this methodology for uses in posture control. |
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Keywords: | Muscle Electrical stimulation Control theory Spinal cord injury |
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