The purpose of this study was to examine the neuromuscular adaptations following 3 and 6 weeks of 80% versus 30% one repetition maximum (1RM) resistance training to failure in the leg extensors. 26 men (mean +/- SD; age = 23.1 +/- 4.7 yrs) were randomly assigned to a high- (80% of 1RM; n = 13) or low-load (30% of 1RM; n = 13) resistance training group and completed leg extension resistance training to failure 3 times per week for 6 weeks. Testing was completed at baseline, 3, and 6 weeks of training. During each testing session, ultrasound muscle thickness (MT) and echo intensity (EI), 1RM strength, and maximal voluntary isometric contraction (MVIC) strength were measured. Percent voluntary activation (VA) and electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF) were measured during MVIC, and during randomly ordered isometric step muscle actions at 10 - 100% of the baseline MVIC. The results indicated that MT increased (2.8 -- 3.0% and 6.0 -- 6.6%) and EI (-3.8% and -6.8%) decreased similarly from Baseline to Week 3 and Baseline to Week 6, respectively, in the 80% and 30% 1RM groups. However, in the 80% 1RM group, 1RM strength increased by 14.7% and 27.7% and MVIC strength increased 11.8% and 28.0% from Baseline to Week 3 and Week 6, respectively. In the 30% 1RM group, 1RM strength decreased by 3.5% and increased by 9.5% and MVIC strength decreased by 4.3% and increased by 13.4% from Baseline to Week 3 and Week 6, respectively. There were similar changes in VA, EMG AMP, and MMG AMP in the 80% and 30% 1RM groups during MVIC. However, there were greater neuromuscular adaptations at submaximal torques in the 80% versus 30% 1RM group, which were evident in the VA, EMG, and MMG responses. Therefore, despite causing similar muscle hypertrophy, 80% 1RM enhanced muscle strength to a greater degree than 30% 1RM and resulted in an increased efficiency of activation that was especially apparent at high contraction intensities (i.e., ∼ 60 -- 100% MVIC). These results suggest differences in the neuromuscular adaptations to high- versus low-load resistance training that may explain the disparate increases in muscle strength despite similar muscle hypertrophy in response to these two training modes.
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机译：这项研究的目的是检查80％的3和6周后对腿部伸肌衰竭的30％一次最大重复训练（1RM）阻力训练后的神经肌肉适应性。将26名男性（平均+/- SD；年龄= 23.1 +/- 4.7岁）随机分配为高抵抗力（1RM的80％； n = 13）或低负荷抵抗力（1RM的30％； n = 13）训练组并完成腿部伸展阻力训练，每周3次，持续6周。测试在基线，训练的第3和第6周完成。在每个测试阶段，均测量了超声肌肉厚度（MT）和回声强度（EI），1RM强度以及最大自愿等距收缩（MVIC）强度。在MVIC期间以及随机有序的等距踏步肌肉动作中，以基线MVIC的10％至100％来测量自愿激活（VA）和肌电图（EMG）和机电图（MMG）振幅（AMP）和平均功率频率（MPF）的百分比。结果表明，从基线到第3周和从基线到第6周，MT分别增加了（2.8-3.0％和6.0-6.6％）和EI（-3.8％和-6.8％）降低，分别为80％和30％1RM组。但是，在80％的1RM组中，从基线到第3周和第6周，1RM强度分别增加了14.7％和27.7％，MVIC强度分别增加了11.8％和28.0％。从基线到第3周和第6周，在30％1RM组中，1RM强度分别下降了3.5％和9.5％，MVIC强度下降了4.3％和13.4％。在MVIC期间，在80％和30％的1RM组中，VA，EMG AMP和MMG AMP的变化相似。但是，在80％和30％的1RM组中，在最大扭矩下神经肌肉的适应性更大，这在VA，EMG和MMG反应中很明显。因此，尽管造成了类似的肌肉肥大，但80％1RM的肌肉力量却比30％1RM的增强程度更大，并导致增加的激活效率，这在高收缩强度下（即MVIC约为60-100％）尤为明显。这些结果表明，高负荷和低负荷阻力训练的神经肌肉适应性差异，可以解释尽管在这两种训练模式下肌肉肥大相似，但肌肉力量却有所不同。
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