Bernabei Michel, van Dieën Jaap H, Maas Huub
Department of Human Movement Sciences, Faculty of Behavioral and Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, The Netherlands.
Department of Human Movement Sciences, Faculty of Behavioral and Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, The Netherlands
J Neurophysiol. 2017 Sep 1;118(3):1677-1689. doi: 10.1152/jn.00625.2016. Epub 2017 May 10.
The aims of this study were to investigate changes ) in the coordination of activation of the triceps surae muscle group, and ) in muscle belly length of soleus (SO) and lateral gastrocnemius (LG) during locomotion (trotting) in response to increased stiffness of intermuscular connective tissues in the rat. We measured muscle activation and muscle belly lengths, as well as hindlimb kinematics, before and after an artificial enhancement of the connectivity between SO and LG muscles obtained by implanting a tissue-integrating surgical mesh at the muscles' interface. We found that SO muscle activation decreased to 62%, while activation of LG and medial gastrocnemius muscles increased to 134 and 125%, respectively, compared with the levels measured preintervention. Although secondary additional or amplified activation bursts were observed with enhanced connectivity, the primary pattern of activation over the stride and the burst duration were not affected by the intervention. Similar muscle length changes after manipulation were observed, suggesting that length feedback from spindle receptors within SO and LG was not affected by the connectivity enhancement. We conclude that peripheral mechanical constraints given by morphological (re)organization of connective tissues linking synergists are taken into account by the central nervous system. The observed shift in activity toward the gastrocnemius muscles after the intervention suggests that these larger muscles are preferentially recruited when the soleus has a similar mechanical disadvantage in that it produces an unwanted flexion moment around the knee. Connective tissue linkages between muscle-tendon units may act as an additional mechanical constraint on the musculoskeletal system, thereby reducing the spectrum of solutions for performing a motor task. We found that intermuscular coordination changes following intermuscular connectivity enhancement. Besides showing that the extent of such connectivity is taken into account by the central nervous system, our results suggest that recruitment of triceps surae muscles is governed by the moments produced at the ankle-knee joints.
本研究的目的是调查大鼠在运动（小跑）过程中，比目鱼肌（SO）和外侧腓肠肌（LG）肌腹长度以及小腿三头肌肌群激活协调性的变化，以应对肌肉间结缔组织刚度增加的情况。我们通过在肌肉界面植入组织整合手术网来人为增强SO和LG肌肉之间的连接性，在此前后测量了肌肉激活、肌腹长度以及后肢运动学参数。我们发现，与干预前测量的水平相比，SO肌肉激活下降至62%，而LG和内侧腓肠肌的激活分别增加至134%和125%。尽管连接性增强后观察到了继发性额外或放大的激活爆发，但整个步幅的主要激活模式和爆发持续时间并未受到干预的影响。操作后观察到类似的肌肉长度变化，这表明SO和LG内梭形感受器的长度反馈不受连接性增强的影响。我们得出结论，连接协同肌的结缔组织形态学（重新）组织所产生的外周机械约束被中枢神经系统所考虑。干预后观察到的活动向腓肠肌转移表明，当比目鱼肌在产生围绕膝关节的不必要屈曲力矩方面具有类似机械劣势时，这些较大的肌肉会被优先募集。肌腱单元之间的结缔组织连接可能对肌肉骨骼系统起到额外的机械约束作用，从而减少执行运动任务的解决方案范围。我们发现肌肉间连接性增强后肌肉间协调性发生了变化。除了表明中枢神经系统会考虑这种连接性的程度外，我们的结果还表明，小腿三头肌的募集受踝关节和膝关节产生的力矩控制。
