Nuzzo James L, Barry Benjamin K, Jones Matthew D, Gandevia Simon C, Taylor Janet L
1Neuroscience Research Australia, Randwick, NSW, AUSTRALIA; 2School of Medical Sciences, University of New South Wales, Kensington, NSW, AUSTRALIA; 3School of Clinical Medicine, University of Queensland, St. Lucia, QLD, AUSTRALIA; 4Prince of Wales Clinical School, University of New South Wales, Kensington, NSW, AUSTRALIA; and 5School of Medical and Health Sciences, Edith Cowan University, Perth, WA, AUSTRALIA.
Med Sci Sports Exerc. 2017 Nov;49(11):2286-2296. doi: 10.1249/MSS.0000000000001367.
Neural adaptations to strength training have long been recognized, but knowledge of mechanisms remains incomplete. Using novel techniques and a design which limited experimental bias, this study examined if 4 wk of strength training alters voluntary activation and corticospinal transmission.
Twenty-one subjects were randomized into strength training (n = 10; 7 females, 3 males; 23.5 ± 7.5 yr; mean ± SD) and control groups (n = 11; 2 females, 9 males; 23.0 ± 4.2 yr). Strength training involved 12 sessions of high-force isometric contractions of the elbow flexors. Before and after training, voluntary activation of the elbow flexors was assessed via transcranial magnetic stimulation. Also, for the first time, magnetic stimulation of corticospinal axons was used to examine spinal-level adaptations to training. The evoked responses, termed cervicomedullary motor-evoked potentials (CMEPs), were acquired in resting biceps brachii in three arm postures. Muscle adaptations were assessed via electrical stimulation of biceps.
Compared with the control group, the strength training group exhibited greater increases in maximal strength (12.8% ± 6.8% vs 0.0% ± 2.7%; P < 0.001), biceps electromyographic activity (27.8% ± 25.9% vs -5.2% ± 16.8%; P = 0.002), and voluntary activation (4.7% ± 3.9% raw change vs -0.1% ± 5.2%; P = 0.034). Biceps CMEPs in all arm postures were unchanged after training. Biceps twitch characteristics were also unchanged.
Four weeks of isometric strength training of the elbow flexors increased muscle strength and voluntary activation, without a change in the muscle. The improvement in activation suggests that voluntary output from the cortex was better able to recruit motoneurons and/or increase their firing rates. The lack of change in CMEPs indicates that neither corticospinal transmission nor motoneuron excitability was affected by training.
长期以来，人们已经认识到神经对力量训练的适应性，但对其机制的了解仍不完整。本研究采用新技术和限制实验偏差的设计，探讨4周的力量训练是否会改变自主激活和皮质脊髓传导。
21名受试者被随机分为力量训练组（n = 10；7名女性，3名男性；23.5±7.5岁；平均值±标准差）和对照组（n = 11；2名女性，9名男性；23.0±4.2岁）。力量训练包括12节肘部屈肌的高强度等长收缩训练。在训练前后，通过经颅磁刺激评估肘部屈肌的自主激活情况。此外，首次使用皮质脊髓轴突的磁刺激来检查训练对脊髓水平的适应性。在三种手臂姿势下，于静息肱二头肌中采集诱发反应，即颈髓运动诱发电位（CMEP）。通过对肱二头肌的电刺激评估肌肉适应性。
与对照组相比，力量训练组在最大力量（12.8%±6.8%对0.0%±2.7%；P < 0.001）、肱二头肌肌电图活动（27.8%±25.9%对 -5.2%±16.8%；P = 0.002）和自主激活（原始变化4.7%±3.9%对 -0.1%±5.2%；P = 0.034）方面有更大的增加。训练后，所有手臂姿势下的肱二头肌CMEP均未改变。肱二头肌的抽搐特征也未改变。
四周的肘部屈肌等长力量训练增加了肌肉力量和自主激活，而肌肉本身没有变化。激活的改善表明，皮质的自主输出能够更好地募集运动神经元和/或提高其放电率。CMEP没有变化表明，训练既不影响皮质脊髓传导，也不影响运动神经元兴奋性。
