NEUROMUSCULAR ADAPTATIONS AFTER 2 AND 4 WEEKS OF 80% VERSUS 30% 1 REPETITION MAXIMUM RESISTANCE TRAINING TO FAILURE

The purpose of this study was to investigate the hypertrophic, strength, and neuromuscular adaptations to 2 and 4 weeks of resistance training at 80 vs. 30% 1 repetition maximum (1RM) in untrained men. Fifteen untrained men (mean +/- SD; age = 21.7 +/- 2.4 years; weight = 84.7 +/- 23.5 kg) were randomly assigned to either a high-load (n = 7) or low-load (n = 8) resistance training group and completed forearm flexion resistance training to failure 3 times per week for 4 weeks. Forearm flexor muscle thickness (MT) and echo intensity, maximal voluntary isometric (MVIC) and 1RM strength, and the electromyographic, mechanomyographic (MMG), and percent voluntary activation (% VA) responses at 10-100% of MVIC were determined at baseline, 2, and 4 weeks of training. The MT increased from baseline (2.9 +/- 0.1 cm) to week 2 (3.0 +/- 0.1 cm) and to week 4 (3.1 +/- 0.1 cm) for the 80 and 30% 1RM groups. MVIC increased from week 2 (121.5 +/- 19.1 Nm) to week 4 (138.6 +/- 22.1 Nm) and 1RM increased from baseline (16.7 +/- 1.6 kg) to weeks 2 and 4 (19.2 +/- 1.9 and 20.5 +/- 1.8 kg) in the 80% 1RM group only. The MMG amplitude at 80 and 90% MVIC decreased from baseline to week 4, and % VA increased at 20 and 30% MVIC for both groups. Resistance training to failure at 80 vs. 30% 1RM elicited similar muscle hypertrophy, but only 80% 1RM increased muscle strength. However, these disparate strength adaptations were difficult to explain with neuromuscular adaptations because they were subtle and similar for the 80 and 30% 1RM groups.