The influence of high-load and combined high- and low-load resistance training on electromyographic behavior during...

To compare the effects of 6 weeks of combined high- and low-load lower body resistance training (H + L) to high-load only training (H) on maximal strength, muscle thickness (MT), and electromyographic (EMG_RMS)-torque relationships of the vastus lateralis during an absolute muscular endurance (AME) task.

Twenty-eight untrained males performed maximal voluntary contractions (MVCs) and trapezoidal muscle actions to failure at the same absolute 50% MVC for the knee extensors before (PRE) and after training (POST_ABS). Individual b- and a-terms were calculated from the log-transformed EMG_RMS-torque relationships during the linearly increasing (LI) and decreasing (LD) segments of the first (FMA) and last muscle action (LMA). The b-terms examine the rate of change in EMG_RMS in relation to torque and the a-terms reflect an upward/downward shifting of the overall relationship without changing EMG_RMS linearity. Steady torque EMG_RMS was normalized (N-EMG_RMS).

After training: maximal strength increased similarly between the groups (p < 0.001). MT increased for both groups (p < 0.001-0.01), but was greater for H + L (p < 0.022). Only H + L improved AME (p < 0.001). The b-terms decreased, whereas the a-terms increased for both groups during the FMA LD and LMA LI (p < 0.001-0.030). N-EMG_RMS for H + L decreased across muscle actions (p < 0.001).

Despite similar increases in strength, only H + L improved AME, exhibited greater hypertrophy, and required less muscle excitation at steady torque. The changes in b- and a-terms suggest reduced muscle excitation was necessary to match torque during the upper regions of FMA LD and LMA LI. Therefore, H + L training may improve strength and endurance, and reduce neural cost during sustained activities.