Comparison of Bipolar and Monopolar Electrode Configurations for FES on Biceps Brachii.

Function electrical stimulation (FES) is recommended as one of the effective methods for rehabilitation of motor function after stroke. There are two forms to deliver electrical stimulation to induce muscle contraction: Bipolar electrode configuration with two electrodes of the same size, and monopolar electrode configuration with a bigger electrode as an indifferent electrode and a smaller one as an active electrode. The purpose of this study is to compare the two kinds of configuration on biceps brachii in terms of induced muscle contraction force and muscle fatigue. In the experiment, electrical stimulation was applied on biceps brachii muscles of the right arm. Isometric contraction was induced by fixing the elbow joint during the stimulation. The experimental results showed that the induced contraction force was bigger using monopolar electrode configuration with the indifferent electrode on the antagonist muscle, and there was no significant difference in muscle fatigue between the configurations. Monopolar electrode configuration with the indifferent electrode on the antagonist muscle was suggested as the most effective method for FES on biceps brachii.Clinical Relevance- This study establishes an effective electrode configuration for FES on biceps brachii.

Investigation of Motor Point Shift and Contraction Force of Triceps Brachii for Functional Electrical Stimulation.

Functional electrical stimulation (FES) has been used for neurorehabilitation of individuals with paralysis due to spinal cord injuries or stroke aftereffects. The biceps brachii is often adopted in studies on FES because of the ease of stimulation, while there are few studies on the triceps brachii. Stimulation of the triceps brachii is important because the biceps brachii tends to be spastic. The aim of this study is to investigate the position shift of the motor points (MPs) of the three main muscle groups in triceps brachii with respect to the elbow joint angle, and the contraction force of the muscle groups. Firstly, MPs were measured in 6 healthy individuals using an MP pen at 5 elbow joint angles. The MPs of the long and lateral heads shifted distally and laterally, and the MPs of the medial head shifted distally and medially as the arm extended. The MPs of the long head shifted farthest of all. Secondly, the contraction force was measured in 9 healthy individuals using a force gauge at elbow joint angle of 90 degrees. Three different voltages were applied: 4, 8, and 12 V. The results showed that the medial head yields a sufficient contraction force although the medial head is situated deeper than the other two muscle groups. These findings will help to better understand the stimulation of the triceps brachii and improve the efficiency of electrical stimulation therapy.

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.

Estimation of handgrip force using frequency-band technique during fatiguing muscle contraction.

In this paper, we propose a force estimation model to compute the handgrip force from SEMG signal during fatiguing muscle contraction tasks. The appropriate frequency range was analyzed using various combinations of a wavelet scale, and the highest accuracy was achieved at a range from 242 to 365 Hz. After that, eight healthy individuals performed a series of static (70%, 50%, 30%, and 20% MVC) and dynamic (0-50% MVC) muscle contraction tasks to evaluate the performance of this technique in comparison with that of former method using the Root Mean Square of the SEMG signal. Both methods had comparable results at the beginning of the experiments, before the onset of muscle fatigue. However, differences were clearly observed as the degree of muscle fatigue began to increase toward the endurance time. Under this condition, the estimated handgrip force using the proposed method improved from 17% to 134% for static contraction tasks and 40% for dynamic contraction tasks. This study overcomes the limitation of the former method during fatiguing muscle contraction tasks and, therefore, unlocks the potential of utilizing the SEMG signal as an indirect force estimation method for various applications.

Quantitative estimation of muscle fatigue using surface electromyography during static muscle contraction.

Muscle fatigue is commonly associated with the musculoskeletal disorder problem. Previously, various techniques were proposed to index the muscle fatigue from electromyography signal. However, quantitative measurement is still difficult to achieve. This study aimed at proposing a method to estimate the degree of muscle fatigue quantitatively. A fatigue model was first constructed using handgrip dynamometer by conducting a series of static contraction tasks. Then the degree muscle fatigue can be estimated from electromyography signal with reasonable accuracy. The error of the estimated muscle fatigue was less than 10% MVC and no significant difference was found between the estimated value and the one measured using force sensor. Although the results were promising, there were still some limitations that need to be overcome in future study.

Simultaneous measurement of force and muscle fatigue using frequency-band wavelet analysis.

Static and dynamic handgrip experiments are performed in order to evaluate the effectiveness of utilizing frequency-band wavelet analysis in measuring force and muscle fatigue simultaneously. SEMG signals are recorded from flexor muscle and analyzed using continuous wavelet transform (CWT). The wavelet coefficients are grouped into high frequency (65Hz - 350Hz) and low frequency (5Hz - 45Hz) band. A significant correlation is discovered between amplitude of high frequency band and force level. On the other hand, the amplitude of low frequency band is associated with muscle fatigue. These results have an important implication for estimating force and muscle fatigue simultaneously especially during dynamic contraction.