Repetition tempo (time under tension)
Deliberately slowing your reps to maximize 'time under tension' does not build more muscle. Muscle growth is similar across a wide range of rep speeds, roughly 0.5 to 8 seconds per rep, and very slow reps (over 10 seconds) appear to be worse. Control the weight, then focus on effort and load instead.
What the science says
- A wide range of tempos builds similar muscle Moderate evidence
Schoenfeld et al.'s 2015 meta-analysis found similar hypertrophy with repetition durations from 0.5 to 8 seconds.
- Very slow reps appear to be worse for growth Limited evidence
The same meta-analysis found that volitionally very slow reps (over 10 seconds) seemed inferior for hypertrophy, but there are few controlled studies, so this is not definitive.
- Tempo changes how much you can lift and how many reps Limited evidence
Wilk et al.'s 2021 review notes that tempo alters load, rep count and volume, which is why it can matter indirectly; the review describes rather than settles how to use it.
- More time under tension means more growth Limited evidence
This popular claim is not supported: within normal tempos, Schoenfeld et al. (2015) found no hypertrophy advantage to longer rep durations.
How to apply it
Use a controlled tempo that lets you keep good form and get close to failure; do not slow down deliberately for 'time under tension'.
Who should be careful
Bouncing or dropping weights uncontrolled increases the risk of strains; keep the lowering phase controlled. Anyone with an injury who has been given a specific tempo by a physiotherapist or other professional should follow that advice.
Frequently asked questions
Does slowing my reps build more muscle?
No. A meta-analysis found similar growth across rep durations of 0.5 to 8 seconds, and very slow reps over 10 seconds appeared worse.
What tempo should I use?
A controlled one, roughly 2–6 seconds per rep, lowering in about 1–3 seconds and lifting as fast as you can with control.
What matters more than tempo?
Taking sets close to failure, using an appropriate load and rep range, and progressing over time.
Scientific references
More training variables
- Training volume (sets per muscle per week) Strong evidence
Weekly volume, counted as hard sets per muscle, is one of the best-supported drivers of muscle growth: more sets bring more growth, with diminishing returns.
- Training frequency (sessions per muscle per week) Moderate evidence
When weekly volume is the same, how many days you split it across makes little difference to muscle growth.
- Rest intervals between sets Moderate evidence
Very short rests (under about a minute) tend to cost you reps and slightly blunt growth; past about 90 seconds, extra rest brings little added hypertrophy.
- Range of motion (full vs partial reps) Moderate evidence
Full range of motion generally builds more strength and lower-body muscle than short, partial reps.
- Exercise order Moderate evidence
Whatever you do first in a session gets stronger the most, so put your priority lifts first.
- Mind-muscle connection (internal focus) Limited evidence
Focusing on squeezing the target muscle does raise its electrical activity with light to moderate loads, and one small long-term trial found more biceps growth with it.