Abstract

Erected posture provides humans a large shoulder mobility that requires complex automatic muscle synergies to accomplish joint stability needs. This is evident in shoulder abduction, wherein the voluntary activation of glenohumeral muscles is coupled with an automatic recruitment of scapulothoracic muscles. Here, we investigated whether volitional modification of the scapular position, and dynamic scapular elevation, modulate the contraction timing of five shoulder muscles (middle deltoid, upper, middle and lower fiber of the trapezius, serratus anterior) during shoulder abduction. The results show matched contraction timings of the deltoid and upper trapezius across the scapular positions, whereas the contraction timings of the middle and lower fibers of the trapezius change secondary to the scapular position. These results might reflect different central strategies to coordinate the automatic sequences of contraction of the scapulothoracic muscles. This suggest a flexible and adaptable predisposition of the motor control system in exploring alternative solutions to accomplish the functional movement needs, such as the fulfillment of unconstrained movements. Intriguingly, the shoulder abduction may represent a powerful, non-invasive, and straightforward tool to deepen the understanding of the neural basis underlying the voluntary motor command modulation of the out-of-volition automatic muscle contractions.

摘要

直立姿势为人类提供了较大的肩部活动能力，这需要复杂的自动肌肉协同作用才能实现关节稳定性需求。这在肩外展中很明显，其中盂肱肌肉的随意激活与肩胛胸肌的自动募集相结合。在这里，我们研究了肩胛骨位置的意志改变和肩胛骨的动态抬高是否会调节肩部外展过程中五块肩部肌肉（三角肌中部、斜方肌上、中、下纤维，前锯肌）的收缩时间。结果显示三角肌和上斜方肌在肩胛骨位置的收缩时间匹配，而斜方肌中下部纤维的收缩时间随肩胛骨位置的变化而变化。这些结果可能反映了不同的中心策略来协调肩胛胸肌收缩的自动序列。这表明运动控制系统在探索实现功能性运动需求的替代解决方案时具有灵活和适应性强的倾向，例如实现不受约束的运动。有趣的是，肩外展可能是一种强大的、非侵入性的、直接的工具，可以加深对无意识自动肌肉收缩的自主运动命令调制的神经基础的理解。这表明运动控制系统在探索实现功能性运动需求的替代解决方案时具有灵活和适应性强的倾向，例如实现不受约束的运动。有趣的是，肩外展可能是一种强大的、非侵入性的、直接的工具，可以加深对无意识自动肌肉收缩的自主运动命令调制的神经基础的理解。这表明运动控制系统在探索实现功能性运动需求的替代解决方案时具有灵活和适应性强的倾向，例如实现不受约束的运动。有趣的是，肩外展可能是一种强大的、非侵入性的、直接的工具，可以加深对无意识自动肌肉收缩的自主运动命令调制的神经基础的理解。