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Neuromuscular adaptations to three and six weeks of high-versus low-load resistance training
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. ^
Jenkins, Nathaniel D.M, "Neuromuscular adaptations to three and six weeks of high-versus low-load resistance training" (2016). ETD collection for University of Nebraska - Lincoln. AAI10100909.