Nóbrega, SR, Ugrinowitsch, C, Pintanel, L, Barcelos, C, and Libardi, CA. Effect of resistance training to muscle failure vs. volitional interruption at high- and low-intensities on muscle mass and strength. J Strength Cond Res 32(1): 162-169, 2018-The purpose of this study was to investigate the effects of resistance training (RT) at high- and low-intensities performed to muscle failure or volitional interruption on muscle strength, cross-sectional area (CSA), pennation angle (PA), and muscle activation. Thirty-two untrained men participated in the study. Each leg was allocated in 1 of 4 unilateral RT protocols: RT to failure at high and low intensities, and RT to volitional interruption (repetitions performed to the point in which participants voluntarily interrupted the exercise) at high (HIRT-V) and low (LIRT-V) intensities. Muscle strength (1 repetition maximum [1RM]), CSA, PA, and muscle activation by amplitude of the electromyography (EMG) signal were assessed before (Pre), after 6 (6W), and 12 (12W) weeks. 1RM increased similarly after 6W (range: 15.8-18.9%, effective size [ES]: 0.41-0.58) and 12W (range: 25.6-33.6%, ES: 0.64-0.98) for all protocols. All protocols were similarly effective in increasing CSA after 6W (range: 3.0-4.6%, ES: 0.10-0.24) and 12W (range: 6.1-7.5%, ES: 0.22-0.26). PA increased after 6W (∼3.5) and 12W (∼9%; main time effect, p < 0.0001), with no differences between protocols. EMG values were significantly higher for the high-intensity protocols at all times (main intensity effect, p < 0.0001). In conclusion, both HIRT-V and LIRT-V are equally effective in increasing muscle mass, strength, and PA when compared with RT performed to muscle failure.

The aim of this study was to compare the effects of resistance training to muscle failure (RT-F) and non-failure (RT-NF) on muscle mass, strength and activation of trained individuals. We also compared the effects of these protocols on muscle architecture parameters. A within-subjects design was used in which 14 participants had one leg randomly assigned to RT-F and the other to RT-NF. Each leg was trained 2 days per week for 10 weeks. Vastus lateralis (VL) muscle cross-sectional area (CSA), pennation angle (PA), fascicle length (FL) and 1-repetition maximum (1-RM) were assessed at baseline (Pre) and after 20 sessions (Post). The electromyographic signal (EMG) was assessed after the training period. RT-F and RT-NF protocols showed significant and similar increases in CSA (RT-F: 13.5% and RT-NF: 18.1%; P < 0.0001), PA (RT-F: 13.7% and RT-NF: 14.4%; P < 0.0001) and FL (RT-F: 11.8% and RT-NF: 8.6%; P < 0.0001). All protocols showed significant and similar increases in leg press (RT-F: 22.3% and RT-NF: 26.7%; P < 0.0001) and leg extension (RT-F: 33.3%, P < 0.0001 and RT-NF: 33.7%; P < 0.0001) 1-RM loads. No significant differences in EMG amplitude were detected between protocols ( P > 0.05). In conclusion, RT-F and RT-NF are similarly effective in promoting increases in muscle mass, PA, FL, strength and activation.