Nitin sharma

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Asymptotic optimal control of neuromuscular electrical stimulation

49th IEEE Conference on Decision and Control (CDC), 2010

Abstract Muscle fatigue during electrical stimulation onsets early and is comparatively more subs... more Abstract Muscle fatigue during electrical stimulation onsets early and is comparatively more substantial than during volitional contractions, hindering successful application of functional and therapeutic neuromuscular electrical stimulation (NMES). One of the avoidable causes of muscle fatigue can be attributed to the overstimulation during NMES. In this paper, a NMES controller is developed to minimize a quadratic cost functional to balance asymptotic trajectory tracking performance and control effort, potentially reducing overstimulation of ...

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Asymptotic tracking by a reinforcement learning-based adaptive critic controller

Journal of Control Theory and Applications, 2011

Adaptive critic (AC) based controllers are typically discrete and/or yield a uniformly ultimately... more Adaptive critic (AC) based controllers are typically discrete and/or yield a uniformly ultimately bounded stability result because of the presence of disturbances and unknown approximation errors. A continuous-time AC controller is developed that yields asymptotic tracking of a class of uncertain nonlinear systems with bounded disturbances. The proposed AC-based controller consists of two neural networks (NNs)-an action NN, also called the actor, which approximates the plant dynamics and generates appropriate control actions; and a critic NN, which evaluates the performance of the actor based on some performance index. The reinforcement signal from the critic is used to develop a composite weight tuning law for the action NN based on Lyapunov stability analysis. A recently developed robust feedback technique, robust integral of the sign of the error (RISE), is used in conjunction with the feedforward action neural network to yield a semiglobal asymptotic result. Experimental results are provided that illustrate the performance of the developed controller.

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Comparing the force- and excursion- frequency relationships in human skeletal muscle

Muscle & Nerve, 2008

We examined the influence of varying stimulation frequency on muscle output during isometric and ... more We examined the influence of varying stimulation frequency on muscle output during isometric and dynamic contractions. Our findings demonstrate that the predictability of the force-and excursion-frequency relationships is extremely strong across stimulation intensities. There were no differences in the frequency which elicited 50% of peak or peak muscle output. We conclude that the impact of varying stimulation frequency is consistent between isometric and dynamic contractions.

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A novel modulation strategy to increase stimulation duration in neuromuscular electrical stimulation

Muscle & Nerve, 2011

Introduction: Neuromuscular electrical stimulation (NMES) has been shown to be an effective treat... more Introduction: Neuromuscular electrical stimulation (NMES) has been shown to be an effective treatment for muscular dysfunction. Yet, a fundamental barrier to NMES treatments is the rapid onset of muscle fatigue. The purpose of this study is to examine the effect of feedback-based frequency modulation on the closed-loop performance of the quadriceps during repeated dynamic contractions. Methods: In the first experiment, subjects completed four different frequency modulation NMES protocols utilizing the same amplitude modulation control to compare the successful run times (SRTs). A second experiment was performed to determine the change in muscle response to high-and low-frequency stimulation. Results: Compared with constant-frequency stimulation, results indicate that using an error-driven strategy to vary the stimulation frequency during amplitude modulation increases the number of successful contractions during non-isometric conditions. Conclusion: Simultaneous frequency and amplitude modulation increases the SRT during closed-loop NMES control.

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