How slow vs fast leg exercises change muscle strength and size
Resistance training with different repetition duration to failure: effect on hypertrophy, strength and muscle activation
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
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.
Surprising Findings
Slow reps improved strength at short muscle lengths, but not overall 1RM or muscle size.
Most people assume slower reps = more growth or strength, but here, slow only helped in one specific angle—and didn’t boost size or full-range strength.
Practical Takeaways
Use slow reps (6 seconds) if you need strength with a nearly straight leg—like in sprinting, kicking, or rehab after knee injury.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
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.
Surprising Findings
Slow reps improved strength at short muscle lengths, but not overall 1RM or muscle size.
Most people assume slower reps = more growth or strength, but here, slow only helped in one specific angle—and didn’t boost size or full-range strength.
Practical Takeaways
Use slow reps (6 seconds) if you need strength with a nearly straight leg—like in sprinting, kicking, or rehab after knee injury.
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.