The increase in muscle force after 4 weeks of strength training is mediated by adaptations in motor unit recruitment and rate coding
The increase in muscle force after 4 weeks of strength training is mediated by adaptations in motor unit recruitment and rate coding
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DOI：
10.1113/jp277250
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发表时间：
2019-04-01
影响因子：
5.5
通讯作者：
Farina, Dario
中科院分区：
文献类型：
--
作者：
Del Vecchio, Alessandro;Casolo, Andrea;Farina, Dario
关键点以前的研究表明，几周的力量训练足以引起发送到肌肉的神经驱动的显著适应。然而，很少有数据的变化引起的力量训练的招聘和率编码的运动单位在自愿收缩。我们第一次表明，在干预跟踪胫骨前肌运动单位的放电特征改变了4周的力量训练等长随意收缩。具体的适应包括运动单位放电率的显着增加，运动单位的募集阈值力和运动神经元的类似的输入-输出增益的下降。研究结果表明，在运动单位功能的适应可能是由于突触输入的运动神经元池的变化或适应内在的运动神经元特性。肌肉的力量通常在几次力量训练后开始增加。这种增加通常归因于神经驱动肌肉的变化，这是皮层或脊髓水平适应的结果。我们研究了踝背屈肌等长收缩力量训练前后胫骨前肌大量纵向追踪运动单位放电特征的变化。14个人表现出的适应与14个对照组进行了比较。采用128个电极的高密度肌电网格记录等长斜坡收缩至最大随意力的35%、50%和70%时的肌电活动。评估运动单位募集和去募集阈值、放电率、峰间期和对运动神经元的突触输入的估计。力量训练后运动单位的标准化募集阈力降低（P < 0.05）。此外，在次最大等长收缩的平台期，放电率增加了3.3 +/- 2.5 pps（受试者和运动单位的平均值）（P < 0.001）。训练对复张和复张时的出院率无影响（P < 0.05）。在收缩的斜坡阶段，力和运动单位放电率之间的关联也没有被训练改变（P < 0.05）。这些结果首次证明，4周力量训练后肌肉力量的增加是从脊髓到肌肉的运动神经元输出增加的结果。
Key pointsPrevious studies have indicated that several weeks of strength training is sufficient to elicit significant adaptations in the neural drive sent to the muscles. There are few data, however, on the changes elicited by strength training in the recruitment and rate coding of motor units during voluntary contractions. We show for the first time that the discharge characteristics of motor units in the tibialis anterior muscle tracked across the intervention are changed by 4 weeks of strength training with isometric voluntary contractions. The specific adaptations included significant increases in motor unit discharge rate, decreases in the recruitment-threshold force of motor units and a similar input-output gain of the motor neurons. The findings suggest that the adaptations in motor unit function may be attributable to changes in synaptic input to the motor neuron pool or to adaptations in intrinsic motor neuron properties. The strength of a muscle typically begins to increase after only a few sessions of strength training. This increase is usually attributed to changes in the neural drive to muscle as a result of adaptations at the cortical or spinal level. We investigated the change in the discharge characteristics of large populations of longitudinally tracked motor units in tibialis anterior before and after 4 weeks of strength training the ankle-dorsiflexor muscles with isometric contractions. The adaptations exhibited by 14 individuals were compared with 14 control subjects. High-density electromyogram grids with 128 electrodes recorded the myoelectric activity during isometric ramp contractions to the target forces of 35%, 50% and 70% of maximal voluntary force. The motor unit recruitment and derecruitment thresholds, discharge rate, interspike intervals and estimates of synaptic inputs to motor neurons were assessed. The normalized recruitment-threshold forces of the motor units were decreased after strength training (P < 0.05). Moreover, discharge rate increased by 3.3 +/- 2.5 pps (average across subjects and motor units) during the plateau phase of the submaximal isometric contractions (P < 0.001). Discharge rates at recruitment and derecruitment were not modified by training (P < 0.05). The association between force and motor unit discharge rate during the ramp-phase of the contractions was also not altered by training (P < 0.05). These results demonstrate for the first time that the increase in muscle force after 4 weeks of strength training is the result of an increase in motor neuron output from the spinal cord to the muscle.