Sahinis Chrysostomos, Amiridis Ioannis G, Kannas Theodoros M, Farina Dario, Enoka Roger M, Kellis Eleftherios
Laboratory of Neuromechanics, Department of Physical Education and Sport Sciences at Serres, Aristotle University of Thessaloniki, Thessaloniki, GREECE.
Department of Bioengineering, Imperial College London, London, UNITED KINGDOM.
Med Sci Sports Exerc. 2024 Dec 1;56(12):2338-2348. doi: 10.1249/MSS.0000000000003530. Epub 2024 Aug 19.
Conflicting results have been reported on the functional role of the proximal and distal compartments of the semitendinosus (ST) muscle. This study compared the discharge characteristics of motor units (MU) in the two compartments at three knee joint angles (0°: long length; 45°: intermediate length; and 90°: short length).
Twenty men (21.4 ± 2.3 yr) performed steady isometric contractions with the knee flexors at four target forces: 10%, 20%, 40%, and 60% of maximum voluntary contraction. High-density EMG signals were recorded to examine the MU discharge characteristics in the two compartments. Measurements included recruitment threshold, mean discharge rate, coefficient of variation (CoV) for interspike interval, and SD of filtered cumulative spike train (fCST). Additionally, the within- and between-compartment association of the neural drive was calculated.
ANOVA indicated that maximal force, absolute EMG amplitude during the maximum voluntary contractions, and force steadiness (CoV for force) were greater at the longest muscle length than the other two lengths ( P < 0.05). Linear mixed models showed that both recruitment threshold and CoV for interspike interval were similar between compartments ( P > 0.05) at each of the three knee joint angles. However, the mean discharge rate and the variability in neural drive were greater for the proximal than the distal compartment ( P < 0.05). The between-compartment association in neural drive (filtered cumulative spike train) was relatively low.
There were distinct differences in MU discharge characteristics between the proximal and the distal compartments of ST across its operating range of muscle lengths, and each compartment received a relatively distinct neural drive. These findings emphasize the importance of recognizing differences in neural control of the ST compartments to guide related interventions and to inform rehabilitation strategies.
关于半腱肌（ST）近端和远端肌室的功能作用，已有相互矛盾的研究结果报道。本研究比较了在三个膝关节角度（0°：长长度；45°：中等长度；90°：短长度）下，两个肌室中运动单位（MU）的放电特征。
20名男性（21.4±2.3岁）以四个目标力进行膝关节屈肌的等长收缩：最大自主收缩的10%、20%、40%和60%。记录高密度肌电信号以检查两个肌室中的MU放电特征。测量指标包括募集阈值、平均放电率、峰间期变异系数（CoV）以及滤波后累积放电序列（fCST）的标准差。此外，还计算了神经驱动在肌室内和肌室间的关联。
方差分析表明，在最长肌肉长度时的最大力量、最大自主收缩期间的绝对肌电幅度以及力量稳定性（力量的CoV）均大于其他两个长度（P<0.05）。线性混合模型显示，在三个膝关节角度中的每一个角度下，两个肌室之间的募集阈值和峰间期CoV均相似（P>0.05）。然而，近端肌室的平均放电率和神经驱动的变异性大于远端肌室（P<0.05）。神经驱动（滤波后累积放电序列）在肌室间的关联相对较低。
在ST肌肉长度的整个工作范围内，近端和远端肌室的MU放电特征存在明显差异，并且每个肌室接受相对不同的神经驱动。这些发现强调了认识ST肌室神经控制差异对于指导相关干预和制定康复策略的重要性。
