Movement, Interactions, Performance, Nantes Université, Nantes, France.
Laboratory of Functional Morphology, Department of Biology, University of Antwerp, Antwerp, Belgium.
J Appl Physiol (1985). 2023 Aug 1;135(2):394-404. doi: 10.1152/japplphysiol.00075.2023. Epub 2023 Jun 22.
We aimed to determine whether the neural control of the biarticular gastrocnemius medialis (GM) and lateralis (GL) muscles is joint-specific, that is, whether their control differs between isolated knee flexion and ankle plantar flexion tasks. Twenty-one male participants performed isometric knee flexion and ankle plantar flexion tasks while we recorded high-density surface electromyography (HDsEMG). First, we estimated the distribution of activation both within- and between muscles using two complementary approaches: surface EMG amplitude and motor unit activity identified from HDsEMG decomposition. Second, we estimated the level of common synaptic input between GM and GL motor units using a coherence analysis. The distribution of EMG amplitude between GM and GL was not different between tasks, which was confirmed by the analysis of motor units' discharge rate. Even though there was a significant proximal shift in GM and GL EMG amplitude during knee flexion compared with ankle plantar flexion, the magnitude of this shift was small and not confirmed via the inspection of the spatial distribution of motor unit action potentials. A significant coherence between GM and GL motor units was only observed for four (knee flexion) and three (ankle plantar flexion) participants, with no difference in the level of coherence between the two tasks. We were able to track only a few motor units across tasks, which raises the question as to whether the same motor units were activated across tasks. Our results suggest that the neural control of the GM and GL muscles is similar across their two main functions. Several studies have focused on the neural strategies used to control the gastrocnemius medialis (GM) and lateralis (GL) during plantar flexion. However, their secondary function, i.e., knee flexion, is not often explored. We observed a robustness of the GM and GL activation strategy across tasks, which was confirmed with an analysis of the motor unit discharge characteristics. The level of common synaptic input between GM and GL motor units was low, regardless of the task.
我们旨在确定双关节腓肠肌内侧（GM）和外侧（GL）肌肉的神经控制是否具有关节特异性，即它们在单独的膝关节屈曲和踝关节跖屈任务中的控制是否不同。 21 名男性参与者在进行等长膝关节屈曲和踝关节跖屈任务时，我们记录了高密度表面肌电图（HDsEMG）。首先，我们使用两种互补的方法来估计肌肉内和肌肉间的激活分布：从 HDsEMG 分解中识别的表面肌电幅度和运动单位活动。其次，我们使用相干性分析来估计 GM 和 GL 运动单位之间的共同突触输入水平。 GM 和 GL 之间的 EMG 幅度分布在任务之间没有差异，这通过运动单位放电率的分析得到了证实。尽管与踝关节跖屈相比，膝关节屈曲时 GM 和 GL 的 EMG 幅度明显向近端转移，但这种转移的幅度很小，并且通过检查运动单位动作电位的空间分布无法得到证实。仅在四个（膝关节屈曲）和三个（踝关节跖屈）参与者中观察到 GM 和 GL 运动单位之间存在显着的相干性，并且两个任务之间的相干性水平没有差异。我们只能在任务之间跟踪几个运动单位，这引发了一个问题，即相同的运动单位是否在任务之间被激活。我们的结果表明，GM 和 GL 肌肉的神经控制在其两个主要功能中是相似的。已有多项研究侧重于控制 GM 和 GL 在跖屈过程中使用的神经策略。然而，它们的次要功能，即膝关节屈曲，并不经常被探索。我们观察到 GM 和 GL 激活策略在任务之间具有稳健性，这通过运动单位放电特性的分析得到了证实。 GM 和 GL 运动单位之间的共同突触输入水平较低，无论任务如何。
