Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill, NC and North Carolina State University, Raleigh, NC, United States of America.
J Neural Eng. 2018 Dec;15(6):066005. doi: 10.1088/1741-2552/aadd1b. Epub 2018 Aug 28.
Weakness of the hand is a major impairment which limits independent living. Neuromuscular electrical stimulation (NMES) is a common approach to help restore muscle strength. Traditional NMES directly over the muscle often leads to a rapid onset of muscle fatigue. In this study, we investigated the force sustainability of finger flexor muscles using a transcutaneous nerve stimulation approach.
Finger flexion forces and high-density electromyogram (HD EMG) signals were obtained while electrical stimulation was applied to the ulnar and median nerve bundles through a stimulation grid on the proximal arm segment. Stimulation was also applied to the finger flexor muscle belly targeting the motor point, serving as a control condition. The force produced from the two stimulation approaches were initially matched, and muscle fatigue was subsequently induced with 5 min of continuous stimulation. The rate of decay of the force and EMG amplitude were quantified, and the spatial distribution of the muscle activation during the sustained contraction was also evaluated.
The proximal nerve stimulation approach induced a slower decay in both force and EMG, compared with the stimulation at the motor point. The spatial distribution of the elicited muscle activation showed that the proximal nerve stimulation led to a distributed activation across the intrinsic and extrinsic finger flexor muscles and also activated a wider area within the extrinsic muscle.
Our findings demonstrated that the stimulation of the proximal nerve bundles can elicit sustained force output and delayed decrease in the rate of force decline. This is potentially due to a spatially distributed activation of the muscle fibers, compared with the traditional motor point stimulation. Future development of our nerve stimulation approach may enable prolonged usage during rehabilitation or assistance for better functional outcomes.
手部无力是一种严重的障碍，限制了患者的独立生活能力。神经肌肉电刺激（NMES）是一种帮助恢复肌肉力量的常用方法。传统的 NMES 直接作用于肌肉往往会导致肌肉迅速疲劳。在这项研究中，我们通过经皮神经刺激的方法研究了手指屈肌的力持续时间。
当通过刺激臂近端段上的刺激网格向尺神经和正中神经束施加电刺激时，获得手指屈肌力量和高密度肌电图（HD EMG）信号。刺激也施加到手指屈肌的肌腹上，以运动点为靶点，作为对照条件。两种刺激方法产生的力最初是匹配的，然后用 5 分钟的连续刺激来诱导肌肉疲劳。量化了力和 EMG 幅度衰减的速率，并评估了在持续收缩期间肌肉激活的空间分布。
与刺激运动点相比，近端神经刺激方法引起的力和 EMG 衰减更缓慢。诱发肌肉激活的空间分布表明，近端神经刺激导致内在和外在手指屈肌的分布式激活，并且在外在肌肉内激活了更广泛的区域。
我们的研究结果表明，刺激近端神经束可以产生持续的力输出，并延迟力下降的速度。这可能是由于与传统的运动点刺激相比，肌肉纤维的空间分布激活。未来我们的神经刺激方法的发展可能会使其在康复或辅助治疗中延长使用时间，从而获得更好的功能结果。
