Lifting speed is described with several overlapping terms, and the research on it measures different outcomes in different groups. This guide reads four PubMed abstracts on 3 November 2026: a 2015 meta-analysis of repetition duration and muscle growth, a 2017 meta-analysis of movement velocity and strength, a 2019 randomised trial of repetition duration, and a 2022 randomised trial of fast and slow tempos. Only the abstracts were used, so details beyond them are not covered. None of the abstracts mentions dumbbells or kettlebells, and this guide makes no claim about them. General information, not training advice.
Four terms, as the abstracts use them
- Repetition duration: the 2015 meta-analysis defines it as the sum total of the concentric, eccentric and isometric components of a repetition, predicated on the tempo at which the repetition is performed. The 2019 trial describes it as the time taken to perform the concentric and eccentric muscle actions.
- Tempo: the 2022 trial compared FAST and SLOW eccentric repetition tempos, written 1-0-1 and 1-0-3 in the abstract.
- Movement velocity: the 2017 meta-analysis treats it as a training variable that can be manipulated and compares fast or explosive training with slower training.
- Time under load (TUL): the 2019 trial matched its groups for load and for time under load.
The 2015 review: hypertrophy and repetition duration
Schoenfeld and colleagues in Sports Medicine included eight studies. Eligible studies were experimental trials that directly compared training tempos, lasted at least 6 weeks, trained to muscle failure, measured muscle changes by biopsy, imaging or densitometry, and used people without a chronic disease or injury. The abstract reports that hypertrophic outcomes are similar when training with repetition durations from 0.5 to 8 seconds. It adds that findings suggest very slow repetitions, over 10 seconds each, are inferior for hypertrophy, but that a lack of controlled studies makes definitive conclusions difficult.
The 2017 review: velocity and strength
Davies and colleagues, also in Sports Medicine, identified 15 studies of healthy adults that compared fast or explosive training with slower training, matched prescribed intensity and volume, and lasted at least 4 weeks. Fast and moderate-slow training produced similar increases in dynamic muscular strength when all studies were included. When intensity was accounted for, the abstract reports a trend for a small effect favouring fast training at moderate intensities, defined as 60 to 79% of one repetition maximum (effect size 0.31, p = 0.06). The abstract calls this a trend. It also reports that strength gains were not influenced by training status and age.
The 2019 trial: three very different speeds
Carlson and colleagues randomised 59 participants to three groups: a 2s:4s repetition (18 people), a 10s:10s repetition (20 people), or a group that performed 30 seconds of eccentric, 30 of concentric and 30 of eccentric action (about 1.5 repetitions, 21 people). Sessions were supervised one-to-one, twice a week for 10 weeks, and the abstract describes the protocol as low-volume, single-set and machine-based, with chest press, leg press and pulldown outcomes. Strength rose significantly for all exercises with no differences between groups, and no statistically significant changes were found in body composition, upper arm and thigh muscle mass or fasted blood glucose. The authors conclude that repetition duration does not affect strength increases in trained participants when exercise is performed to momentary failure.
The 2022 trial: one leg fast, one leg slow
Pearson and colleagues had 13 resistance-trained men train each leg with a different tempo, chosen at random, for 8 weeks, twice weekly, using a single-joint leg extension. Strength (one repetition maximum) rose in both legs: by 17.0% on the FAST leg and 22.1% on the SLOW leg. Muscle thickness at the proximal thigh rose similarly. At the distal thigh the increase was greater on the FAST leg, 5.5% against 2.2%. The SLOW leg had a higher rating of perceived exertion (8.59 against 7.98). The authors conclude that both tempos produced similar muscular adaptations but suggest FAST may give a small hypertrophic advantage at the distal quadriceps.
Why the four results are kept apart
- Different outcomes: the 2015 review measured muscle growth, the 2017 review measured strength, and the two trials measured both.
- Different speeds: the reviews compared repetition durations or velocities pooled from many studies, the 2019 trial compared three very different repetition durations, and the 2022 trial compared two eccentric tempos.
- Different people and exercises: people without chronic disease or injury (2015) and healthy adults (2017) in the reviews, 59 trained men and women on machines in 2019, and 13 trained men on one leg exercise in 2022.
A result from machine exercises or a leg extension does not describe free weight work, and the abstracts do not test it.
What the abstracts do not say
They do not recommend a tempo for any individual, compare speeds with other training variables, or report on beginners lifting free weights. The 2015 review notes a lack of controlled studies. The 2022 trial had 13 participants, and its authors describe the hypertrophy advantage as small and the adaptations as regional.
The bottom line
The 2015 meta-analysis reports similar hypertrophy for repetition durations from 0.5 to 8 seconds. The 2017 meta-analysis reports similar strength gains from fast and moderate-slow training, with a non-significant trend favouring fast at moderate intensities. The 2019 trial found no strength differences between three repetition durations in 10 weeks, and the 2022 trial found similar strength gains on fast and slow legs with a small difference in distal thigh thickness. These come from abstracts, from different outcomes and groups, and none covers dumbbells or kettlebells.
Sources
- Effect of repetition duration during resistance training on muscle hypertrophy: a systematic review and meta-analysis, Schoenfeld and colleagues, Sports Medicine, April 2015 (abstract, PubMed), read 3 November 2026 (pubmed.ncbi.nlm.nih.gov)
- Effect of Movement Velocity During Resistance Training on Dynamic Muscular Strength: A Systematic Review and Meta-Analysis, Davies and colleagues, Sports Medicine, August 2017 (abstract, PubMed), read 3 November 2026 (pubmed.ncbi.nlm.nih.gov)
- Neither repetition duration nor number of muscle actions affect strength increases, body composition, muscle size, or fasted blood glucose in trained males and females, Carlson and colleagues, Applied Physiology, Nutrition, and Metabolism, February 2019 (abstract, PubMed), read 3 November 2026 (pubmed.ncbi.nlm.nih.gov)
- Does Varying Repetition Tempo in a Single-Joint Lower Body Exercise Augment Muscle Size and Strength in Resistance-Trained Men?, Pearson and colleagues, Journal of Strength and Conditioning Research, 2022 (abstract, PubMed), read 3 November 2026 (pubmed.ncbi.nlm.nih.gov)
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