The effects of exercise variation in muscle thickness, maximal strength and motivation in resistance trained men

PLoS One. 2019 Dec 27;14(12):e0226989. doi: 10.1371/journal.pone.0226989. eCollection 2019.


Background: The objective of the present study was to compare the effects of a traditional resistance training program (fixed exercises and repetition ranges) to a resistance training program where exercises and repetition ranges were randomized on a session-by-session basis on markers of muscular adaptations and intrinsic motivation.

Methods: Twenty-one resistance trained men were randomized to perform an 8-week resistance training program using either a fixed exercise selection (CON) or having exercises randomly varied each session via a computerized app. Both groups performed 3 sets of 6 exercises, with training carried out 4 times per week.

Results: Both conditions promoted large, statistically significant increases in the bench press and back-squat 1 repetition maximum without differences between groups. Muscle thickness (MT) measures for the individual quadriceps showed large, statistically significant increases in of the vastus lateralis and rectus femoris for both conditions, with no observed between-group differences. Although no between-group in MT were noted for the vastus intermedius, only the CON displayed significant increases from baseline. Participants in EXP showed a significant, moderate improvement in the intrinsic motivation to training, while participants in the CON group presented non-significant decreases in this variable.

Conclusions: Varying exercise selection had a positive effect on enhancing motivation to train in resistance-trained men, while eliciting similar improvements in muscular adaptations.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Body Composition
  • Humans
  • Male
  • Motivation
  • Muscle Strength*
  • Muscle, Skeletal / physiology
  • Resistance Training / methods*
  • Young Adult

Associated data

  • figshare/10.6084/m9.figshare.9879737.v1

Grants and funding

This is study was supported by the Basque Government research group IT1381-19.The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.