Leonardis Joshua M, Alkayyali Amani A, Lipps David B
School of Kinesiology, University of Michigan, Ann Arbor, Michigan.
Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan.
J Neurophysiol. 2020 Apr 1;123(4):1526-1535. doi: 10.1152/jn.00702.2019. Epub 2020 Feb 26.
The execution of activities of daily living requires the generation of three-dimensional shoulder torques through the coordinated activations of 20 shoulder muscles. Changes in shoulder posture can influence the contributions of individual shoulder muscles to shoulder torque generation, but it is unclear how the coordinated activity of shoulder muscles changes with shoulder plane of elevation and elevation angle. The purpose of this study was to characterize how neuromuscular coordination underlying three-dimensional shoulder function varies with arm posture. Muscle activations were obtained using surface electromyography from 16 shoulder muscles, as 12 healthy participants repeated eight three-dimensional isometric shoulder torques in 20 arm postures. Nonnegative matrix factorization revealed the muscle synergies underlying shoulder torque generation across each of the experimental postures, while the normalized similarity index assessed changes in overall synergy structure and linear mixed-effects models assessed changes in the weighted contributions of individual muscles to each synergy. Our analysis revealed that three distinct muscle synergies underlie healthy three-dimensional shoulder function. The overall structure of these synergies remained more similar than is expected by chance, despite changes in shoulder posture. However, the weighted contributions of five muscles composing the first synergy were influenced by changes in shoulder plane of elevation angle, and six muscles composing the second synergy were influenced by elevation angle. The weighted contributions of individual muscles composing the third synergy were unaffected by posture. These findings suggest that the neuromuscular control plan for healthy shoulder function consists of three distinct synergies, whose overall structure is fixed across shoulder posture. This study is the first to identify the muscle synergies underlying three-dimensional isometric shoulder torque generation. Although the overall structure of these synergies was unaffected by arm posture, the weighted contributions of several muscles composing two synergy patterns changed as a function of the elevation or plane of elevation of the shoulder. Our findings provide valuable insight for the development of targeted interventions for the restoration of shoulder function after neuromuscular or orthopedic pathologies.
日常生活活动的执行需要通过20块肩部肌肉的协同激活来产生三维肩部扭矩。肩部姿势的变化会影响单个肩部肌肉对肩部扭矩产生的贡献，但尚不清楚肩部肌肉的协同活动如何随肩部抬高平面和抬高角度而变化。本研究的目的是描述三维肩部功能背后的神经肌肉协调如何随手臂姿势而变化。当12名健康参与者在20种手臂姿势下重复进行8次三维等长肩部扭矩测试时，使用表面肌电图获取了16块肩部肌肉的激活情况。非负矩阵分解揭示了每个实验姿势下肩部扭矩产生背后的肌肉协同作用，而标准化相似性指数评估了整体协同结构的变化，线性混合效应模型评估了单个肌肉对每个协同作用的加权贡献的变化。我们的分析表明，健康的三维肩部功能背后有三种不同的肌肉协同作用。尽管肩部姿势发生了变化，但这些协同作用的整体结构仍然比随机预期的更为相似。然而，构成第一种协同作用的五块肌肉的加权贡献受肩部抬高平面角度变化的影响，构成第二种协同作用的六块肌肉受抬高角度的影响。构成第三种协同作用的单个肌肉的加权贡献不受姿势影响。这些发现表明，健康肩部功能的神经肌肉控制计划由三种不同的协同作用组成，其整体结构在肩部姿势中是固定的。本研究首次确定了三维等长肩部扭矩产生背后的肌肉协同作用。尽管这些协同作用的整体结构不受手臂姿势的影响，但构成两种协同模式的几块肌肉的加权贡献随肩部的抬高或抬高平面而变化。我们的研究结果为开发针对神经肌肉或骨科疾病后肩部功能恢复的靶向干预措施提供了有价值的见解。
