Contraction level, but not force direction or wrist position, affects the spatial distribution of motor unit recruitment in the biceps brachii muscle
Contraction level, but not force direction or wrist position, affects the spatial distribution of motor unit recruitment in the biceps brachii muscle
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DOI：
10.1007/s00421-020-04324-6
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发表时间：
2020-02-19
影响因子：
3
通讯作者：
Vieira, Taian M.
中科院分区：
文献类型：
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作者：
Borzelli, Daniele;Gazzoni, Marco;Vieira, Taian M.
目的肱二头肌（BB）中不同的运动单位（MU）在屈肘或旋后时被优先募集。这些不同的单位是否居住在不同的地区是一个悬而未决的问题。在这项研究中，我们测试了MUs是否招募在次最大的等长任务的肘部屈曲和旋后两个收缩水平，并与手腕固定在两个不同的角度是空间定位在不同的BB部分。方法采用电极网格（沿着BB纵轴4行，16列中-外侧）对12名受试者BB肌的高密度表面肌电信号（EMG）进行分解，提取MU的放电瞬间。然后使用击发瞬间触发和平均单差EMG。分别计算每个信号的平均整流值，并保留网格中沿着每列的最大值。质量中心定义为各列最大平均校正值的加权平均值，然后用于评估条件之间MU表面表示的内外侧变化。结果收缩水平，但没有手腕的位置，也没有力的方向（屈曲与旋后），影响BB MU的空间分布。特别是，更高的力与BB MU的募集，其动作电位更内侧表示。结论虽然BB MUs的动作电位在肌肉内外侧区域局部表现，但从MUs动作电位的表面表现来看，不太可能区分屈肘和旋后。
Purpose Different motor units (MUs) in the biceps brachii (BB) muscle have been shown to be preferentially recruited during either elbow flexion or supination. Whether these different units reside within different regions is an open issue. In this study, we tested wheter MUs recruited during submaximal isometric tasks of elbow flexion and supination for two contraction levels and with the wrist fixed at two different angles are spatially localized in different BB portions. Methods The MUs' firing instants were extracted by decomposing high-density surface electromyograms (EMG), detected from the BB muscle of 12 subjects with a grid of electrodes (4 rows along the BB longitudinal axis, 16 columns medio-laterally). The firing instants were then used to trigger and average single-differential EMGs. The average rectified value was computed separately for each signal and the maximal value along each column in the grid was retained. The center of mass, defined as the weighted mean of the maximal, average rectified value across columns, was then consdiered to assess the medio-lateral changes in the MU surface representation between conditions. Results Contraction level, but neither wrist position nor force direction (flexion vs. supination), affected the spatial distribution of BB MUs. In particular, higher forces were associated with the recruitment of BB MUs whose action potentials were represented more medially. Conclusion Although the action potentials of BB MUs were represented locally across the muscle medio-lateral region, dicrimination between elbow flexion or supination seems unlikely from the surface representation of MUs action potentials.