School of Kinesiology, University of Michigan , Ann Arbor, Michigan.
Department of Biomedical Engineering, University of Michigan , Ann Arbor, Michigan.
J Appl Physiol (1985). 2018 May 1;124(5):1297-1303. doi: 10.1152/japplphysiol.00892.2017. Epub 2018 Feb 8.
Neck muscles are preferentially activated in specific force directions, but the constraints that the central nervous system considers when programming these preferred directions of muscle activity are unknown. The current study used ultrasound shear wave elastography (SWE) to investigate whether the material properties of the sternocleidomastoid (SCM) muscles exhibit preferred directions similar to their preferred direction of muscle activity during an isometric task. Twenty-four healthy participants matched isometric forces in 16 axial directions. All force targets were scaled to 20% of a maximum voluntary contraction. Muscle activity was recorded with surface electromyography (EMG) from six muscles (the bilateral SCMs, upper trapezius, and splenius capitis muscles), and shear wave velocities (SWVs) were recorded with SWE from both SCM muscles. We observed statistically significant differences between the preferred directions of muscle activity and SWVs for both the left SCM ( P = 0.002) and the right SCM ( P < 0.001), with the SWE data exhibiting a more lateral preferred direction. Significant differences in the spatial focus ( P < 0.001) were also observed, with the dispersion of SWV data covering a greater angular range than the EMG data during isometric tasks. The preferred directions of muscle activity and material properties for the SCM muscles were closer than previous comparisons of muscle activity and moment arms, suggesting muscle mechanics could play a more important role than anatomy in how the central nervous system spatially tunes muscle activation. NEW & NOTEWORTHY Our study used a novel combination of surface electromyography and ultrasound shear wave elastography to investigate the neuromuscular control of the neck. Our work highlights differences in how the activation and material properties of the sternocleidomastoid muscles are modulated as the central nervous system stabilizes the neck during isometric force production. These findings provide normative data for future studies to investigate pathologic changes to both the activation and material properties of the sternocleidomastoid muscles.
颈部肌肉在特定的力方向上优先激活，但中枢神经系统在规划这些肌肉活动的首选方向时所考虑的约束条件尚不清楚。本研究使用超声剪切波弹性成像（SWE）来研究胸锁乳突肌（SCM）的力学特性是否在等长任务中表现出与肌肉活动首选方向相似的首选方向。24 名健康参与者在 16 个轴向方向上匹配等长力。所有力目标均缩放到最大自主收缩的 20%。使用表面肌电图（EMG）从六块肌肉（双侧 SCM、上斜方肌和头夹肌）记录肌肉活动，并使用 SWE 从双侧 SCM 肌肉记录剪切波速度（SWV）。我们观察到左侧 SCM（ P = 0.002）和右侧 SCM（ P < 0.001）的肌肉活动首选方向和 SWV 之间存在统计学上的显著差异，SWE 数据表现出更偏向外侧的首选方向。在空间焦点上也观察到显著差异（ P < 0.001），在等长任务中，SWV 数据的分散范围大于 EMG 数据。SCM 肌肉的肌肉活动首选方向和力学特性之间的差异比之前肌肉活动和力矩臂的比较更接近，这表明肌肉力学在中枢神经系统如何在空间上调整肌肉激活方面可能比解剖结构更重要。本研究使用表面肌电图和超声剪切波弹性成像的新组合来研究颈部的神经肌肉控制。我们的工作强调了在等长力产生过程中，中枢神经系统稳定颈部时，胸锁乳突肌的激活和力学特性是如何被调节的。这些发现为未来研究提供了规范数据，以研究胸锁乳突肌的激活和力学特性的病理变化。
