Vasavada Anita N, Peterson Barry W, Delp Scott L
Programs in Bioengineering and Neuroscience, P.O. Box 646520, Washington State University, Pullman, WA 99164-6520, USA.
Exp Brain Res. 2002 Dec;147(4):437-48. doi: 10.1007/s00221-002-1275-6. Epub 2002 Oct 18.
The complex structure of the neck musculoskeletal system poses challenges to understanding central nervous system (CNS) control strategies. Examining muscle activation patterns in relation to musculoskeletal geometry and three-dimensional mechanics may reveal organizing principles. We analyzed the spatial tuning of neck muscle electromyographic (EMG) activity while subjects generated moments in three dimensions. EMG tuning curves were characterized by their orientation (mean direction) and focus (spread of activity). For the four muscles that were studied (sternocleidomastoid, splenius capitis, semispinalis capitis and trapezius), EMG tuning curves exhibited directional preference, with consistent orientation and focus among 12 subjects. However, the directional preference (orientation) of three of the four neck muscles did not correspond to the muscle's moment arm, indicating that maximizing a muscle's mechanical advantage is not the only factor in determining muscle activation. The focus of muscle tuning did not change with moment magnitude, demonstrating that co-contraction did not increase with load. Axial rotation was found to have a strong influence on neck muscle spatial tuning. The uniform results among subjects indicate that the CNS has consistent strategies for selecting neck muscle activations to generate moments in specific directions; however, these strategies depend on three-dimensional mechanics in a complex manner.
颈部肌肉骨骼系统的复杂结构给理解中枢神经系统（CNS）的控制策略带来了挑战。研究与肌肉骨骼几何结构和三维力学相关的肌肉激活模式可能会揭示其组织原则。我们在受试者进行三维力矩生成时，分析了颈部肌肉肌电图（EMG）活动的空间调谐情况。EMG调谐曲线通过其方向（平均方向）和焦点（活动范围）来表征。对于所研究的四块肌肉（胸锁乳突肌、头夹肌、头半棘肌和斜方肌），EMG调谐曲线表现出方向偏好，12名受试者之间具有一致的方向和焦点。然而，四块颈部肌肉中的三块的方向偏好（方向）与肌肉的力臂并不对应，这表明最大化肌肉的机械优势并非决定肌肉激活的唯一因素。肌肉调谐的焦点不会随力矩大小而变化，这表明协同收缩不会随负荷增加。发现轴向旋转对颈部肌肉空间调谐有很大影响。受试者之间的一致结果表明，中枢神经系统具有一致的策略来选择颈部肌肉激活以在特定方向上产生力矩；然而，这些策略以复杂的方式依赖于三维力学。
