Behavior of motor units during submaximal isometric contractions in chronically strength-trained individuals
Behavior of motor units during submaximal isometric contractions in chronically strength-trained individuals
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DOI：
10.1152/japplphysiol.00192.2021
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发表时间：
2021-11-01
影响因子：
3.3
通讯作者：
Farina, Dario
中科院分区：
文献类型：
--
作者：
Casolo, Andrea;Del Vecchio, Alessandro;Farina, Dario
神经和形态的适应结合在一起，在长时间接受力量训练后增强了肌肉力量，尽管它们的相对重要性尚不清楚。我们研究了运动单位（MU）行为和肌肉大小对长期力量训练的运动员（ST）与未经训练的对照组（UT）的亚最大力量产生的贡献。16名ST（年龄：22.9 +/- 3.5年；训练经验：5.9 +/- 3.5年）和14名UT（年龄：20.4 +/- 2.3年）用肘关节屈肌进行了最大自主等距力（MViF）和斜坡收缩（MViF分别为15%、35%、50%和70%），同时记录了肱二头肌（BB）的高密度表面肌电图（HDsEMG）。评估了从次最大收缩中识别的mu的招募阈值（RTs）和放电率（DRs）。从力（Delta force，即肌肉输出）的变化与MU DR （DDR，即神经输入）的变化之间的关系来估计神经驱动到肌肉增益。并用MRI评估BB最大解剖截面积（ACSA(MAX)）。MViF （+64.8%, P < 0.001）和BB ACSA(MAX) （+71.9%, P < 0.001）在ST组较高，绝对MU RT在ST组较高（+62.6%,P < 0.001），但发生在相似的归一化力下。在相同的归一化力下，两组间的MU DR无差异。δ FORCE - δ DR关系的绝对斜率在ST中较高（+66.9%,P = 0.002），而在标准化值中没有差异。我们观察到ST运动员和UT对照组之间相似的MU行为。对于相同的神经输入，ST的绝对发力能力更大，这表明形态因素，而不是神经因素，是它们在次极大努力时增强发力的主要机制。在这项研究中，我们观察到力量训练运动员的肱二头肌的大量运动单位的招募策略和放电特征与未训练的个体在次最大力量任务中观察到的相似。我们还发现，对于相同的神经输入，经过力量训练的运动员能够产生更大的绝对肌肉力量（即，神经驱动到肌肉增益）。这表明形态因素是次极大力过程中增强力产生的主要机制。
Neural and morphological adaptations combine to underpin the enhanced muscle strength following prolonged exposure to strength training, although their relative importance remains unclear. We investigated the contribution of motor unit (MU) behavior and muscle size to submaximal force production in chronically strength-trained athletes (ST) versus untrained controls (UT). Sixteen ST (age: 22.9 +/- 3.5 yr; training experience: 5.9 +/- 3.5 yr) and 14 UT (age: 20.4 +/- 2.3 yr) performed maximal voluntary isometric force (MViF) and ramp contractions (at 15%, 35%, 50%, and 70% MViF) with elbow flexors, whilst high-density surface electromyography (HDsEMG) was recorded from the biceps brachii (BB). Recruitment thresholds (RTs) and discharge rates (DRs) of MUs identified from the submaximal contractions were assessed. The neural drive-to-muscle gain was estimated from the relation between changes in force (Delta FORCE, i.e. muscle output) relative to changes in MU DR (DDR, i.e. neural input). BB maximum anatomical cross-sectional area (ACSA(MAX)) was also assessed by MRI. MViF (+64.8% vs. UT, P < 0.001) and BB ACSA(MAX) (+71.9%, P < 0.001) were higher in ST. Absolute MU RT was higher in ST (+62.6%, P < 0.001), but occurred at similar normalized forces. MU DR did not differ between groups at the same normalized forces. The absolute slope of the Delta FORCE - Delta DR relationship was higher in ST (+66.9%, P = 0.002), whereas it did not differ for normalized values. We observed similar MU behavior between ST athletes and UT controls. The greater absolute force-generating capacity of ST for the same neural input demonstrates that morphological, rather than neural, factors are the predominant mechanism for their enhanced force generation during submaximal efforts.NEW & NOTEWORTHY In this study, we observed that recruitment strategies and discharge characteristics of large populations of motor units identified from biceps brachii of strength-trained athletes were similar to those observed in untrained individuals during submaximal force tasks. We also found that for the same neural input, strength-trained athletes are able to produce greater absolute muscle forces (i.e., neural drive-to-muscle gain). This demonstrates that morphological factors are the predominant mechanism for the enhanced force generation during submaximal efforts.