Lifting tempo, the speed at which each repetition is performed, is often presented as a secret: slow the lowering phase, pause at the bottom, count to three on the way up. What does the research say? This article summarises a 2015 systematic review and meta-analysis by Schoenfeld, Ogborn and Krieger, and a 2021 controlled study by Lacerda and colleagues, and reports each at the strength it supports.
What “repetition duration” means
The 2015 review defines repetition duration as the sum total of the concentric (lifting), eccentric (lowering) and isometric (pause) components of a repetition, determined by the tempo at which it is performed. The authors describe it as an often overlooked variable compared with exercise selection, exercise order, rest intervals, load and training volume, and they asked whether changing it can amplify the muscle-growth response to resistance training.
The 2015 meta-analysis
Studies were eligible if they were experimental trials in English-language refereed journals that directly compared different training tempos in dynamic exercise using both concentric and eccentric repetitions, measured changes in muscle by biopsy, imaging or densitometry, lasted at least six weeks, trained to muscle failure, and used human participants without chronic disease or injury. Eight studies met those criteria. The results indicate that hypertrophic outcomes are similar when repetition durations range from 0.5 to 8 seconds. The authors conclude that, for maximising muscle growth, a fairly wide range of repetition durations can be used. They add that training at volitionally very slow durations, over 10 seconds per repetition, appears inferior from a hypertrophy standpoint, but that a lack of controlled studies makes it difficult to draw definitive conclusions.
A 2021 controlled study
Lacerda and colleagues, writing in PeerJ, compared two 14-week protocols in ten untrained men. Each participant’s legs were assigned to different protocols using unilateral knee extension, one with 2-second repetitions and one with 6-second repetitions. Both used 3 to 4 sets at 50 to 60 per cent of one-repetition maximum, with 3 minutes of rest, and were performed to muscle failure. The researchers measured muscle cross-sectional area, isometric strength at two knee angles, and one-repetition maximum. They found that:
- gains in one-repetition maximum and in the cross-sectional area of the rectus femoris and vastus lateralis were not significantly different between the two protocols;
- the 6-second protocol produced larger gains in isometric strength at a knee angle of 30 degrees;
- gains in isometric strength at 90 degrees did not differ significantly.
The authors conclude that longer repetition duration could suit those seeking greater isometric strength gains in shortened knee positions, but that similar dynamic strength and muscle growth would be obtained from either.
Why both tempos can work
The 2021 authors offer an explanation, framed as a possibility rather than a proven mechanism. The 6-second protocol had an average time under tension about 25 per cent longer than the 2-second protocol (43 seconds against 30 seconds), while the 2-second protocol involved twice the number of repetitions per set (14 against 7) and showed higher muscle electrical activity. They suggest that the higher volume and activation of the faster protocol may have counterbalanced the longer time under tension of the slower one.
How strong is this evidence?
- The 2015 review included eight studies, and its authors stress a lack of controlled studies at very slow durations.
- The 2021 study involved ten untrained men and one exercise, the knee extension, so it cannot be generalised to women, trained lifters or other exercises.
- The meta-analysis included only trials in which sets were taken to muscle failure, defined as the inability to complete another concentric repetition with proper form, so its conclusions apply to sets performed that way rather than to sets stopped well short of failure.
- Both sources concern muscle growth and strength measures in healthy adults training to failure; neither examines injury risk, cardio machines or specific equipment products.
Practical points when comparing equipment
Neither source studied tempo-counting consoles, apps or attachments, so the research cannot show that such features improve results. Because the reviewed range of 0.5 to 8 seconds produced similar hypertrophic outcomes, the evidence gives no reason to treat a tempo counter as essential for muscle growth. A buyer who wants to vary repetition speed can simply check, on a demonstration, that a machine or cable stack moves smoothly at both faster and slower speeds.
Frequently asked questions
Is slower always better?
No. The meta-analysis found similar hypertrophy across 0.5 to 8 seconds per repetition, and very slow repetitions over 10 seconds appeared inferior, with caveats.
Does tempo change strength gains?
In the 2021 study, dynamic strength gains were similar between 2-second and 6-second protocols, while isometric strength at 30 degrees improved more with the slower protocol.
The bottom line
Current evidence from a meta-analysis of eight studies suggests that a wide range of repetition durations, from 0.5 to 8 seconds, produces similar muscle growth when training to failure, and a small 2021 trial found similar strength and size gains at 2 and 6 seconds. Neither source tested tempo-counting features, and the conclusions come with clear limits on sample size and population.
Sources
- Schoenfeld BJ, Ogborn DI, Krieger JW, “Effect of repetition duration during resistance training on muscle hypertrophy: a systematic review and meta-analysis”, Sports Medicine, 2015 (PubMed)
- Lacerda LT et al., “Resistance training with different repetition duration to failure: effect on hypertrophy, strength and muscle activation”, PeerJ, 2021 (PubMed Central)