Joint angle based motor point tracking stimulation for surface FES: A Study on biceps brachii

Functional electrical stimulation (FES) has been an effective treatment option in clinical rehabilitation such as motor function recovery after stroke. The main limitation of FES is the lack of stimulation efficiency in motor unit recruitment compared with voluntary contractions, which may cause the early onset of muscle fatigue. The stimulation efficiency of FES can be improved by optimizing electrode positions to target the motor point (MP). However, the location of MP relative to the skin may shift with the change of muscle geometry during dynamic exercise. Hence, the purpose of this study is to maintain the stimulation efficiency of FES in dynamic exercise by switching the stimulation position to follow the shift of MP. We first measured the shift of the MP of the biceps brachii with respect to the elbow joint angle, and then conducted an experiment to compare four stimulation methods: 2-channel simultaneous stimulation (SS), 2-channel time based shifting stimulation (TSS), 2-channel joint angle based shifting stimulation (JASS), and 3-channel JASS. TSS and JASS were designed as two different MP tracking strategies. The experimental results show that the 3-channel JASS caused the smallest decrease in the maximal elbow angle and the angular velocity. The results also suggest that MP tracking stimulation based on joint angle is effective for the sustainable induction of muscle contraction. Both tracking selectivity and tracking density were shown to be important to improve the stimulation efficiency of FES. (C) 2020 IPEM. Published by Elsevier Ltd. All rights reserved.

Automated summary

Functional electrical stimulation (FES) is an effective treatment option for motor function recovery, but its efficiency in motor unit recruitment is limited compared to voluntary contractions. This study aimed to improve the stimulation efficiency of FES during dynamic exercise by tracking the motor point (MP) shift. The results showed that a 3-channel joint angle based shifting stimulation (JASS) method caused the least decrease in maximal elbow angle and angular velocity, suggesting that MP tracking based on joint angle is effective for sustainable muscle contraction induction. Both tracking selectivity and density were found to be important for improving FES efficiency.