Department of Physiology, Northwestern University, Chicago, IL 60611.
Department of Biomedical Engineering, Northwestern University, Evanston, IL.
Proc Natl Acad Sci U S A. 2020 Apr 7;117(14):8135-8142. doi: 10.1073/pnas.1916578117. Epub 2020 Mar 23.
Many studies have demonstrated covariation between muscle activations during behavior, suggesting that muscles are not controlled independently. According to one common proposal, this covariation reflects simplification of task performance by the nervous system so that muscles with similar contributions to task variables are controlled together. Alternatively, this covariation might reflect regulation of low-level aspects of movements that are common across tasks, such as stresses within joints. We examined these issues by analyzing covariation patterns in quadriceps muscle activity during locomotion in rats. The three monoarticular quadriceps muscles (vastus medialis [VM], vastus lateralis [VL], and vastus intermedius [VI]) produce knee extension and so have identical contributions to task performance; the biarticular rectus femoris (RF) produces an additional hip flexion. Consistent with the proposal that muscle covariation is related to similarity of muscle actions on task variables, we found that the covariation between VM and VL was stronger than their covariations with RF. However, covariation between VM and VL was also stronger than their covariations with VI. Since all vastii have identical actions on task variables, this finding suggests that covariation between muscle activity is not solely driven by simplification of overt task performance. Instead, the preferentially strong covariation between VM and VL is consistent with the control of internal joint stresses: Since VM and VL produce opposing mediolateral forces on the patella, the high positive correlation between their activation minimizes the net mediolateral patellar force. These results provide important insights into the interpretation of muscle covariations and their role in movement control.
许多研究表明，在行为过程中肌肉的激活存在共变，这表明肌肉不是独立控制的。根据一个常见的提议，这种共变反映了神经系统通过简化任务表现来控制肌肉，使得对任务变量有相似贡献的肌肉一起被控制。或者，这种共变可能反映了对跨任务常见的运动的低水平方面的调节，例如关节内的应力。我们通过分析大鼠在运动过程中股四头肌活动的共变模式来研究这些问题。三个单关节股四头肌（股直肌内侧[VM]、股直肌外侧[VL]和股直肌中间[VI]）产生膝关节伸展，因此对任务表现有相同的贡献；双关节股直肌（RF）产生额外的髋关节屈曲。与肌肉共变与肌肉对任务变量的动作相似性有关的建议一致，我们发现 VM 和 VL 之间的共变比它们与 RF 的共变更强。然而，VM 和 VL 之间的共变也比它们与 VI 的共变更强。由于所有的股四头肌在任务变量上都有相同的动作，这一发现表明肌肉活动的共变不仅仅是由明显任务表现的简化驱动的。相反，VM 和 VL 之间的优先强共变与关节内应力的控制一致：由于 VM 和 VL 在髌骨上产生相反的内外力，它们的激活之间的高度正相关最小化了髌骨的净内外力。这些结果为解释肌肉共变及其在运动控制中的作用提供了重要的见解。
