Department of Kinesiology and Health Education, University of Texas at Austin, Austin, Texas, United States.
J Neurophysiol. 2024 Sep 1;132(3):617-627. doi: 10.1152/jn.00431.2023. Epub 2024 Jul 17.
Neuromuscular fatigue induces superior migration of the humeral head in individuals with subacromial pain. This has been attributed to weakness of rotator cuff muscles and overactive deltoid muscles. Investigation of common inputs to motoneuron pools of the rotator cuff and deltoid muscles offers valuable insight into the underlying mechanisms of neuromuscular control deficits associated with subacromial pain. This study aims to investigate intermuscular coherence across the rotator cuff and deltoid muscles during a sustained submaximal isometric fatiguing contraction in individuals with and without subacromial pain. Twenty symptomatic and 18 asymptomatic young adults participated in this study. Surface electromyogram (EMG) was recorded from the middle deltoid (MD) and infraspinatus (IS). Intramuscular EMG was recorded with fine-wire electrodes in the supraspinatus (SS). Participants performed an isometric fatiguing contraction of 30° scaption at 25% maximum voluntary contraction (MVC) until endurance limit. Pooled coherence of muscle pairs (SS-IS, SS-MD, IS-MD) in the 2-5 Hz (delta), 5-15 Hz (alpha), and 15-35 Hz (beta) frequency bands during the initial and final 30 s of the fatigue task were compared. SS-IS and SS-MD delta-band coherence increased with fatigue in the asymptomatic group but not the symptomatic group. In the alpha and beta bands, SS-IS and SS-MD coherence increased with fatigue in both groups. IS-MD beta-band coherence was greater in the symptomatic than the asymptomatic group. Individuals with subacromial pain failed to increase common drive across rotator cuff and deltoid muscles and have altered control strategies during neuromuscular fatigue. This may contribute to glenohumeral joint instability and subacromial pain experienced by these individuals. Through the computation of shared neural drive across glenohumeral muscles, this study reveals that individuals with subacromial pain were unable to increase shared neural drive within the rotator cuff and across the supraspinatus and deltoid muscles during neuromuscular fatigue induced by sustained isometric contraction. These deficits in common drive across the shoulder muscles likely contribute to the joint instability and pain experienced by these individuals.
神经肌肉疲劳会导致患有肩峰下疼痛的个体的肱骨头部向上迁移。这归因于肩袖肌肉的虚弱和三角肌的过度活跃。对肩袖和三角肌运动神经元池的常见输入的研究为研究与肩峰下疼痛相关的神经肌肉控制缺陷的潜在机制提供了有价值的见解。本研究旨在研究患有和不患有肩峰下疼痛的个体在持续进行最大等长疲劳收缩期间，肩袖和三角肌之间的肌肉间相干性。20 名有症状和 18 名无症状的年轻成年人参加了这项研究。从中部三角肌（MD）和肩胛下肌（IS）记录表面肌电图（EMG）。使用细电线电极在冈上肌（SS）中记录肌内 EMG。参与者以 25%最大自主收缩（MVC）进行 30°外展等长疲劳收缩，直到耐力极限。在疲劳任务的初始和最后 30 秒期间，在 2-5 Hz（δ）、5-15 Hz（α）和 15-35 Hz（β）频带中比较肌肉对（SS-IS、SS-MD、IS-MD）的总体相干性。在无症状组中，SS-IS 和 SS-MD δ 波段相干性随疲劳而增加，但在有症状组中则不然。在α和β波段中，SS-IS 和 SS-MD 相干性在两组中均随疲劳而增加。IS-MD β 波段相干性在有症状组中大于无症状组。患有肩峰下疼痛的个体无法增加肩袖和三角肌之间的共同驱动力，并在神经肌肉疲劳期间改变控制策略。这可能导致这些个体的盂肱关节不稳定和肩峰下疼痛。通过计算盂肱关节肌肉之间的共享神经驱动，本研究表明，患有肩峰下疼痛的个体在持续等长收缩引起的神经肌肉疲劳期间，无法增加肩袖内和冈上肌和三角肌之间的共享神经驱动。这些肩部肌肉之间共同驱动力的缺陷可能导致这些个体的关节不稳定和疼痛。
