The Study
Resistance training with different repetition duration to failure: effect on hypertrophy, strength and muscle activation
This study compares two ways of lifting weights in the same group of people, like testing two different ways of doing homework on the same student. It can show which method seemed to work better, but it can't prove one causes better results because we didn’t randomly assign and blind the participants like in a stricter experiment.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
Two groups of leg exercises were tested: one slow (6 seconds per move) and one fast (2 seconds per move), both done until muscles were too tired to continue. The slow version made legs stronger when pushing from a bent position, but both versions made muscles grow the same amount.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 545 / 100
Quality score
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1The difference in strength at a bent knee might help athletes or rehab patients who need strength in specific positions, but for general muscle growth or overall strength, both speeds work just as well.
- 2After 14 weeks: 1) Slow reps were better for strength at a bent knee (30°).
- 32) Both reps grew muscles equally.
- 43) Both improved 1-rep max strength the same.
- 54) Slow reps worked muscles harder at the end of the move; fast reps worked harder at the start.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
PeerJ
Year
2021
Authors
L. T. Lacerda, R. O. Marra-Lopes, M. Lanza, R. Diniz, F. V. Lima, H. Martins-Costa, G. Pedrosa, André Gustavo Pereira Andrade, A. Kibele, M. H. Chagas
Related Content
Claims (6)
If you lift weights until your muscles can't do another rep, it helps scientists measure muscle growth in a consistent way over time.
If new guys do leg exercises to failure using medium weights, slowing down the movement doesn’t make their muscles grow more than doing faster reps — both ways work about the same.
If new guys do leg exercises with slow reps (6 seconds) instead of faster ones (2 seconds), they might get stronger in a specific knee position—even if they do the same number of sets and their muscles grow the same amount.
If untrained guys do leg extensions slowly (6 seconds per rep) vs. quickly (2 seconds), they’ll push harder at the end of the movement with the slow version, but harder at the start with the fast one — so speed changes where you’re strongest during the lift.
If untrained guys do leg exercises to failure using medium-heavy weights, going slow or going a bit faster on each rep gives about the same strength gains.
When untrained guys do leg extensions with a medium weight until they can't do any more, moving faster (2 seconds per rep) makes their quads work harder for most of the movement — but moving slower (6 seconds per rep) makes them work harder right at the end. So, how fast you lift changes which part of the move your muscles feel most.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.