Divergent Resistance Training Alters Neuromuscular Behavior Of The Vastus Lateralis During An Absolute Muscular Endurance Task

PURPOSE: To compare the effects of 6 weeks of combined high- and low-load lower body resistance training (H + L) with high-load only training (H) on electromyographic amplitude (EMGRMS)-torque relationships of the vastus lateralis (VL) during an absolute muscular endurance task. METHODS: Twenty-eight healthy untrained men (age = 24 ± 5 yrs) were randomized into the H (n = 14) or H + L (n = 14). Before (PRE) and after (POST) training, participants performed maximal voluntary isometric contractions (MVC) of the knee extensors on a dynamometer followed by submaximal trapezoidal contractions to failure at the same absolute 50% MVC as PRE. Surface EMG signals were collected from the VL during the trapezoidal contractions. b (slopes) terms were calculated from the log-transformed EMGRMS-torque relationships during the linearly increasing (LI) and decreasing (LD) segments of the first and last contraction completed. EMGRMS was normalized (N-EMGRMS) during steady torque. Two separate 2-way mixed factorial repeated measures ANOVAs (group [H vs. H + L] x time [PRE vs. POST]) were performed to examine potential differences in MVC and number of contractions completed. A 4-way mixed factorial repeated measures ANOVA (group x time x contraction [first vs. last] x segment [LI vs. LD]) was used to examine differences in the b terms. A 3-way mixed factorial repeated measures ANOVA (group x time x contraction) was used to examine potential differences in N-EMGRMS. RESULTS: For MVC, there was only a main effect for time (p < 0.05). MVC increased at POST when collapsed across groups. For contractions completed, there was a 2-way interaction (p < 0.05). Only H + L increased the number of contractions completed at POST. For the b terms, there was only a 3-way interaction for time x contraction x segment (p < 0.05). The b terms during the LD segment of the first contraction decreased from PRE to POST, but increased during the LI segment of the last contraction when collapsed across groups. For N-EMGRMS, there was only a 2-way interaction for time x group (p < 0.05). Only H + L decreased N-EMGRMS at POST when collapsed across contractions. CONCLUSIONS: Despite a similar increase in MVC and adjustments in the b terms during the LI segment of both contractions after training, only H + L improved their absolute muscular endurance while requiring less muscle excitation.