Neuromuscular electrical stimulation (NMES) is commonly used in clinical settings to activate skeletal muscle in an effort to mimic voluntary contractions and enhance the rehabilitation of human skeletal muscles. It is also used as a tool in research to assess muscle performance and/or neuromuscular activation levels. However, there are fundamental differences between voluntary- and artificial-activation of motor units that need to be appreciated before NMES protocol design can be most effective. The unique effects of NMES have been attributed to several mechanisms, most notably, a reversal of the voluntary recruitment pattern that is known to occur during voluntary muscle contractions. This review outlines the assertion that electrical stimulation recruits motor units in a nonselective, spatially fixed, and temporally synchronous pattern. Additionally, it synthesizes the evidence that supports the contention that this recruitment pattern contributes to increased muscle fatigue when compared with voluntary actions and provides some commentary on the parameters of electrical stimulation as well as emerging technologies being developed to facilitate NMES implementation. A greater understanding of how electrical stimulation recruits motor units, as well as the benefits and limitations of its use, is highly relevant when using this tool for testing and training in rehabilitation, exercise, and/or research.

Motor unit recruitment during neuromuscular electrical stimulation: a critical appraisal.

Extremum seeking from 1922 to 2010

This paper presents fuzzy approximation-based adaptive backstepping control of an exoskeleton for human upper limbs to provide forearm movement assistance so that a human forearm can track any continuous desired trajectory (or constant setpoint) in the presence of parametric/functional uncertainties, unmodeled dynamics, actuator dynamics, and/or disturbances from environments. Given the desired trajectories of human forearm positions, in the developed control, adaptive fuzzy approximators are used to estimate the dynamical uncertainties of the human–robot system, and an iterative learning scheme is utilized to compensate for unknown time-varying periodic disturbances. With the synthesis of the backstepping, iterative learning, and Lyapunov function approaches, the developed controller does not require exact knowledge of the exoskeleton model, and the close-loop system can be proven to be semiglobally uniformly bounded. Three comparison experiments are conducted to illustrate the effectiveness of the proposed control scheme by tracking periodic/repeated trajectories.

Fuzzy Approximation-Based Adaptive Backstepping Control of an Exoskeleton for Human Upper Limbs

A high-level objective of neuromuscular electrical stimulation (NMES) is to enable a person to achieve some functional task. Towards this goal, the objective of the current effort is to develop a NMES controller to produce a knee position trajectory that will enable a human shank to track any continuous desired trajectory (or constant setpoint). A nonlinear control method is developed to control the human quadriceps femoris muscle undergoing nonisometric contractions. The developed controller does not require a muscle model and can be proven to yield asymptotic stability for a nonlinear muscle model in the presence of bounded nonlinear disturbances (e.g., spasticity, delays, fatigue). The performance of the controller is demonstrated through a series of closed-loop experiments on human subjects. The experiments illustrate the ability of the controller to enable the leg shank to track single and multiple period trajectories with different periods and ranges of motion, and also track desired step changes with changing loads.

/pdf/nonlinear-neuromuscular-electrical-stimulation-tracking-2psgiaqzfq.pdf

Nonlinear Neuromuscular Electrical Stimulation Tracking Control of a Human Limb

Unknown time-varying input delay compensation for uncertain nonlinear systems

An optimal extremum seeking approach is developed in this paper to identify frequency and voltage modulation parameters for a neuromuscular electrical stimulation control objective. The control objective is to externally apply optimally varied voltage or frequency modulation parameters to a human quadriceps muscle to generate a desired knee joint angle. Experimental results are provided to illustrate the limb positioning performance of a real-time extremum seeking routine (i.e., Brent's Method).

An extremum seeking method for non-isometric neuromuscular electrical stimulation

A nonlinear control method is developed in this paper that uses neuromuscular electrical stimulation to control the human quadriceps femoris muscle undergoing non- isometric contractions. The objective of the controller is to position the lower limb of a human along a time-varying trajectory or a desired setpoint. The developed controller does not require a muscle model and can be proven to yield asymptotic stability for a nonlinear muscle model in the presence of bounded nonlinear disturbances. Performance of the controller is illustrated in the provided experimental results.

/pdf/nonlinear-tracking-control-of-a-human-limb-via-neuromuscular-4tme7ir011.pdf

Nonlinear tracking control of a human limb via neuromuscular electrical stimulation

The nonlinear control method explored in this paper uses voltage modulation for controlling human quadriceps femoris muscle undergoing non-isometric neuromuscular electrical stimulation. The control objective is to provide computer controlled stimulation to enable the lower limb of a human to either go to a desired constant position or follow a time-varying desired trajectory. An advantage of the developed controller is that it is robust to nonlinear disturbances and does not require a muscle model. Experimental results are provided that illustrate the performance of the controller.

Experimental demonstration of RISE-based NMES of human quadriceps muscle

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Nonlinear Neuromuscular Electrical Stimulation Tracking Control of a Human Limb

An extremum seeking method for non-isometric neuromuscular electrical stimulation

Nonlinear tracking control of a human limb via neuromuscular electrical stimulation

Experimental demonstration of RISE-based NMES of human quadriceps muscle