Functional Electrical Stimulation (FES) Control for Restoration and Rehabilitation of Motor Function

Functional Electrical Stimulation (FES) Control for Restoration and Rehabilitation of Motor Function

Takashi Watanabe (Tohoku University, Japan) and Naoto Miura (Tohoku University, Japan)
DOI: 10.4018/978-1-4666-2196-1.ch009
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Abstract

Functional electrical stimulation (FES) has been studied and clinically applied to restoring or assisting motor functions lost due to spinal cord injury or cerebrovascular disease. Electrical stimulation without control of functional movements is also used for therapy or in rehabilitation training. In recent years, one of the main focuses of FES studies has been its application for rehabilitation of motor function. In this review, the authors first present the basics of applying electrical stimulation to the neuromuscular system for motor control. Then, two methods of FES control are discussed: controllers for FES based on feedback error learning (FEL) and on cycle-to-cycle control of limb movements. The FEL-FES controller can be practical in FES applications that need to control the musculoskeletal system that involves various nonlinear characteristics and delay in its responses to electrical stimulation. The cycle-to-cycle control is expected to be effective in controlling repetitive movements for rehabilitation training. Finally, a study on ankle dorsiflexion control during the swing phase using an integrated system of FES control and motion measurement with wearable sensors for rehabilitation is presented.
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Basics Of Fes For Assisting And Restoring Motor Functions

Waveforms of voltage or current stimulation, like those shown in Figure 1, are used in FES applications. When using a monophasic pulse (Figure 1a), the DC component of the pulse is eliminated by a capacitor or transformer to prevent the electrolyzation of stimulation electrodes and damage to the tissue. A charge-balanced biphasic pulse (Figure 1b) can also be used to eliminate the DC component. The biphasic pulse has the advantages that the stimulation effect is larger than that of a monophasic pulse of the same amplitude (), and the biphasic pulse makes it possible to activate 2 different parts simultaneously in TES (Ogura et al., 2006). Figure 1c shows bursts from several kilohertz to 50 kHz carried by a sine or rectangular wave. Burst wave stimulation is sometimes used to reduce discomfort at the surface electrical stimulation that produces larger muscle contraction force. However, high frequency burst wave stimulation may result in rapid muscle fatigue.

Figure 1.

Electrical stimulation waveforms used in assisting and restoring motor function with FES. : pulse amplitude, : pulse width, : pulse frequency

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