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Self-selected vs. Fixed Repetition Duration: Effects on Number of Repetitions and Muscle Activation in Resistance-Trained Men

Nóbrega, Sanmy Rocha1; Barroso, Renato2; Ugrinowitsch, Carlos3; da Costa, Jean Lucas Fernandes1; Alvarez, Ieda Fernanda1; Barcelos, Cintia1; Libardi, Cleiton Augusto1

The Journal of Strength & Conditioning Research: September 2018 - Volume 32 - Issue 9 - p 2419–2424
doi: 10.1519/JSC.0000000000002493
Original Research

Nóbrega, SR, Barroso, R, Ugrinowitsch, C, da Costa, JLF, Alvarez, IF, Barcelos, C, and Libardi, CA. Self-selected vs. fixed repetition duration: effects on number of repetitions and muscle activation in resistance-trained men. J Strength Cond Res 32(9): 2419–2424, 2018—The aim of this study was to compare the effects of self-selected and fixed repetition duration (RD) on resistance exercise (RE) volume, muscle activation, and time under tension (TUT) per repetition and per session. Twelve resistance-trained men participated in the study. A randomized cross-over design was used and each participant performed 2 high-intensity RE protocols in a balanced order: (a) 3 sets of RE with self-selected RD (SELF); and (b) 3 sets of RE with fixed RD (2-second concentric and 2-second eccentric [FIX]). Muscle activation was assessed through surface electromyography (EMG) of the vastus lateralis and vastus medialis throughout RE sessions. Overall, RE volume was significantly greater for SELF (p = 0.01), whereas TUT per repetition was significantly greater for FIX (p = 0.0001). No significant differences between protocols were detected for TUT per session. Between-protocol comparisons revealed significantly greater EMG amplitude for SELF compared with FIX at S1 (p = 0.01), S2 (p = 0.03), and S3 (p = 0.03). Both SELF and FIX protocols produced significant increases in EMG amplitude from 25 to 100% (p < 0.001) of set completion. Between-protocol comparisons revealed significantly greater EMG amplitude for SELF compared with FIX at 75% (p = 0.03) and 100% (p = 0.01). In conclusion, self-selected RD resulted in greater volume and muscle activation compared with fixed RD in an RE session.

1MUSCULAB—Laboratory of Neuromuscular Adaptations to Resistance Training, Department of Physical Education, Federal University of São Carlos—UFSCar, São Carlos, São Paulo, Brazil;

2Faculty of Physical Education, University of Campinas—UNICAMP, Campinas, São Paulo, Brazil; and

3School of Physical Education and Sport, University of São Paulo—USP, São Paulo, São Paulo, Brazil

Address correspondence to Dr. Cleiton Augusto Libardi,

Copyright © 2018 by the National Strength & Conditioning Association.