Are 8 to 12 reps best for building muscle?
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They’re a good default, but there’s nothing special about them. In the 2026 American College of Sports Medicine (ACSM) review, weights from 30% to 100% of a person’s max built similar muscle at similar effort, so light weights for many reps and heavy weights for few both work if the set ends close to failure. 8 to 12 wins on time and comfort. Go heavier if you want to lift the most weight once.
Walk into any gym and someone will tell you there are three rep zones. Heavy sets of 1 to 5 build strength, 8 to 12 build size, and 15 or more build endurance or “toning”. It’s called the repetition continuum, and it’s in textbooks, on posters and in most apps. Step outside 8 to 12 and you’re supposedly wasting the set. The strength part holds up well, but newer studies found the zone for size is much wider than the poster says.
What we’d do
Use 8 to 12 reps, or close to it, for most of your sets, because it builds muscle in the fewest minutes with the least misery. For size, do the big lifts for 6 to 10 reps and the small moves for 10 to 15. For strength, do the big lifts for 4 to 6 reps, around 80 to 85% of your max, and the small moves for 8 to 12. Either way, end every set 1 to 3 reps short of failure, so the last reps are slow and hard but clean.
Where 8 to 12 came from
It starts with an army doctor. In 1945, Thomas DeLorme was rebuilding the legs of injured soldiers, who were filling US military hospitals at the end of World War II. He had them lift their heaviest 10-rep weight for several sets, and by 1948 he’d settled on three progressively heavier sets of ten. DeLorme also proposed that heavy loads build strength and light loads build endurance, and that idea grew into the repetition continuum.
The modern version puts strength at 1 to 5 reps with 80 to 100% of your max, size at 8 to 12 reps with 60 to 80%, and endurance at 15 or more with under 60%. In 2009 the American College of Sports Medicine recommended loads of 8 to 12 reps for new lifters, and an emphasis on 6 to 12 for size.
What the studies found
Light against heavy
21 studies, Journal of Strength and Conditioning Research, 2017
Muscle grew about the same with light weights (60% of max or less) as with heavy ones, and one-rep max rose more with heavy weights.
Every set in these studies went all the way to failure, which most people don’t do.
No ideal zone
Schoenfeld, Grgic, Van Every and Plotkin, Sports, 2021
Growth was similar across loads from about 30% of max and up, and the authors wrote that “there is no ideal hypertrophy zone”. Heavy loads were best for one-rep max.
Few of the studies included women.
The biggest review
137 reviews, more than 30,000 people, ACSM, 2026
Loads from 30% to 100% of max built similar muscle at similar effort. Strength rose most with loads of 80% of max or more.
The reviews weren’t split by age, so the advice covers everyone together.
Similar effort means the sets end at about the same distance from failure. Ten easy reps with a weight you could lift 30 times won’t do much, because the set never got hard.
Why 8 to 12 is still a good default
The 2021 review made a practical case for moderate loads. Light weights need many more reps to get close to failure, which takes longer, and the burn from the acid that builds up in the muscle makes those sets unpleasant and harder to stick with. Heavy weights needed more sets to grow the same muscle as moderate ones, and piling up lots of heavy sets adds stress on the joints. Moderate loads sit between the two, and the authors called them the most efficient way to build muscle.
Picking a rep range is like picking a route across town. The highway, the side streets and the scenic road all end at the same place, as long as you actually drive there, and 8 to 12 is the highway.
| Reps per set | What it builds most | The catch |
|---|---|---|
| About 1 to 5 | The most one-rep max strength, and muscle too | It takes more sets to grow the same muscle, with more strain on the joints |
| 6 to 12 | Muscle and strength together, in the least time | Very little, which is why it’s the default |
| 15 to 30 | About the same muscle, if the last reps are hard | Longer sets and a lot of burn |
When heavier wins
If your goal is a bigger squat or bench press max, heavy sets do win. The ACSM found strength rose most with loads of 80% of your max or more, and the 2021 review found heavy loads were needed for the biggest one-rep max. How many reps that is depends on the person. A 2024 analysis of 7,289 people in 269 studies found an average of about 5 reps at 90% of max and about 15 at 70%, with a wide spread between people and more reps on the leg press than the bench press. Go by feel, with the last reps slow and hard, and use the one-rep max calculator to turn any set into a percent table.
6 sources
- Todd JS, Shurley JP and Todd TC, Thomas L. DeLorme and the science of progressive resistance exercise, Journal of Strength and Conditioning Research, 2012europepmc.org
- American College of Sports Medicine, Position stand: progression models in resistance training for healthy adults, Medicine and Science in Sports and Exercise, 2009europepmc.org
- Schoenfeld BJ and others, Strength and hypertrophy adaptations between low- vs. high-load resistance training: a systematic review and meta-analysis, Journal of Strength and Conditioning Research, 2017europepmc.org
- Schoenfeld BJ, Grgic J, Van Every DW and Plotkin DL, Loading recommendations for muscle strength, hypertrophy, and local endurance: a re-examination of the repetition continuum, Sports (Basel), 2021pmc.ncbi.nlm.nih.gov
- Currier BS and others, ACSM position stand: resistance training prescription for muscle function, hypertrophy, and physical performance in healthy adults, Medicine and Science in Sports and Exercise, 2026pmc.ncbi.nlm.nih.gov
- Nuzzo JL and others, Maximal number of repetitions at percentages of the one repetition maximum: a meta-regression and moderator analysis of sex, age, training status, and exercise, Sports Medicine, 2024pmc.ncbi.nlm.nih.gov
