The triceps surae is comprised of the soleus, and medial (MG) and lateral (LG) gastrocnemii. Modulation of triceps surae motor units (MUs) is context- and muscle-dependent, yet it is unknown how the disparate components of the triceps surae work together to achieve the common goal of high-intensity voluntary isometric plantar flexion torque gradation. Thus, the purpose was to assess the interrelationships between MU recruitment thresholds (MURTs) and MU discharge rates (MUDRs) among these three muscles during contractions from low to high intensities. We sampled 157 MU action potential trains from the MG (68), LG (38) and soleus (51) using fine-wire intramuscular electromyography (EMG) during voluntary ramp isometric contractions up to 100% maximal voluntary contraction (MVC). The soleus exhibited 41% and 54% lower MURTs compared to the MG (p < 0.0001) and LG (p < 0.0001), respectively, whereas MG MURTs were 22% lower than the LG (p < 0.0001). Initial MUDRs were 35% and 26% greater for the LG compared with the MG (p < 0.0001) and soleus (p < 0.0001), but no difference was detected between the MG and soleus (p = 0.28). Finally, initial MUDRs displayed a positive relationship with MURTs for each independent triceps surae component (p ≤ 0.002). The relative differences in MU properties of each muscle in this synergistic group illustrate that MU control strategies are likely optimized with respect to the relative contribution of each muscle to plantar flexion torque or functional roles.

中文翻译：

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人体三头肌肱三头肌分离成分对运动单位特性的差异调节。

肱三头肌由比目鱼，内侧（MG）和外侧（LG）腓肠肌组成。肱三头肌运动单位（MUs）的调节取决于上下文和肌肉，但是尚不清楚肱三头肌的不同组成部分如何协同工作以实现高强度自愿等距足底屈曲扭矩分级的共同目标。因此，目的是评估从低强度到高强度收缩期间这三块肌肉之间的MU征服阈值（MURT）和MU放电率（MUDR）之间的相互关系。我们在高达100％的最大自主收缩期间，使用细线肌内肌电图（EMG）对来自MG（68），LG（38）和比目鱼（51）的157个MU动作电位进行了采样。比目鱼比MG的MURT降低41％和54％（p < 0.0001）和LG（p <0.0001），而MG MURT比LG（p <0.0001）低22％。LG的初始MUDR比MG（p <0.0001）和比目鱼（p <0.0001）高35％和26％，但MG和比目鱼之间没有发现差异（p = 0.28）。最后，对于每个独立的肱三头肌部位，初始MUDR与MURT呈正相关（p≤0.002）。在该协同组中，每条肌肉的MU特性的相对差异表明，就每条肌肉对plant屈扭矩或功能作用的相对贡献而言，MU控制策略可能是最佳的。0001和比目鱼（p <0.0001），但在MG和比目鱼之间未发现差异（p = 0.28）。最后，对于每个独立的肱三头肌部位，初始MUDR与MURT呈正相关（p≤0.002）。在该协同组中，每条肌肉的MU特性的相对差异说明，就每条肌肉对足底屈曲扭矩或功能作用的相对贡献而言，MU控制策略很可能是最佳的。0001和比目鱼（p <0.0001），但在MG和比目鱼之间未发现差异（p = 0.28）。最后，对于每个独立的肱三头肌部位，初始MUDR与MURT呈正相关（p≤0.002）。在该协同组中，每条肌肉的MU特性的相对差异说明，就每条肌肉对足底屈曲扭矩或功能作用的相对贡献而言，MU控制策略很可能是最佳的。