The short version
- A meta-analysis of 140 studies and 1,433 effect sizes found maximal strength gains at a mean training intensity of 60% of one-rep max in untrained people and 80% in trained people.
- The same analysis found untrained lifters gained most training each muscle group three days a week and trained lifters two days a week, with four sets per muscle group maximal for both.
- In a meta-regression of 34 treatment groups, each additional weekly set was associated with a 0.37% greater gain in muscle size, and higher within-study volumes produced a 3.9% percentage-gain difference.
- Over eight weeks in 43 trained lifters, progressing repetitions at a constant load produced essentially the same muscle and strength outcomes as progressing load at constant repetitions.
- Grouping weekly sets into fewer than 5, 5 to 9, and 10 or more per muscle produced only a trend rather than a significant effect (P = 0.074), so the exact volume prescription is less settled than it is often presented.
Everything else on this blog is an argument about margins — a few percent here, a small effect size there, an ingredient that helps in a narrow window. This one is about the part that is not a margin. If the demand on the muscle does not increase over time, nothing else in the plan has anything to work with.
The variables that actually move strength
Rhea and colleagues meta-analysed 140 studies producing 1,433 effect sizes, and found that the answer depends on how trained you already are. Training at a mean intensity of 60% of one-rep max elicited maximal gains in untrained individuals, while 80% was most effective in trained ones. Untrained participants got maximal gains from training each muscle group three days a week; trained individuals from two. Four sets per muscle group produced maximal gains in both groups.
That last finding is easy to skim past and worth sitting with. Beyond a point, more sets stopped adding. And the intensity that works for a beginner is not the intensity that works for someone three years in — which is the whole principle in one sentence: what constitutes overload is defined relative to what you have already adapted to.
Volume, and how graded the dose-response really is
For muscle size specifically, Schoenfeld, Ogborn and Krieger meta-regressed 34 treatment groups from 15 studies. Weekly sets treated as a continuous variable had a significant effect on muscle size (P = 0.002): each additional weekly set was associated with a 0.37% greater percentage gain. Comparing higher against lower volumes within each study also showed a significant effect, with a percentage-gain difference of 3.9%.
The honest caveat is in the third analysis. When weekly sets were grouped into fewer than 5, 5 to 9, and 10 or more per muscle, the effect was only a trend (P = 0.074). So the direction is clear and graded; the exact prescription is not as settled as the confident numbers circulating online suggest.
Overload does not have to mean more weight
This is the most practically useful finding in the cluster, because it removes the main reason people stall. Plotkin and colleagues randomised 43 trained lifters to eight weeks of either increasing load while keeping reps constant, or increasing reps while keeping load constant. Four sets of four lower-body exercises, twice a week.
Rectus femoris growth modestly favoured the repetition group (2.8 mm summed across sites, CI -0.5 to 5.8). Dynamic strength slightly favoured the load group (2.0 kg, CI -2.4 to 7.8). The authors describe both differences as of questionable practical significance, and found no other notable between-group differences — muscle thicknesses under 1 mm apart, endurance under 1%, jump height 0.1 cm. Their conclusion: both progressions are viable strategies.
So on a week where the next plate is not happening, adding two reps at the same weight is not a compromise. It is the same principle in a different currency.
Where supplements sit relative to this
They sit downstream, and it is worth being explicit about the scale difference. A caffeine dose improves a session. Creatine lets you do slightly more work per session across months. A pre-workout supplement affects the ninety minutes you are in the building. Overload is the variable that operates on the year, and no ingredient substitutes for it — which is why we would rather someone spent an hour writing down what they lifted than an hour comparing labels.
The related trap is thinking overload means grinding. It does not: two meta-analyses found training to failure was not required for strength or size, and in trials where volume was allowed to fall naturally, stopping short came out ahead for strength. Overload is about the trend line across months, not the suffering in any given set.
What we'd actually tell you
Write down every working set — exercise, weight, reps. Without a record you cannot tell progress from a good mood. Aim to beat the previous entry on something: a rep, a kilo, a cleaner set at the same numbers. Train each muscle group two to three times a week depending on your experience, and treat around four sets per muscle group per session as the point where the evidence stops clearly rewarding you for more.
When load stalls, progress reps. When both stall for a few weeks, look at sleep, food and total weekly volume before you look at a tub. And expect the rate to slow — the intensity finding says beginners and trained lifters need different stimuli, which is a polite way of saying the second year is harder than the first for everybody.
Good questions
What does progressive overload actually mean?
It means the demand on the muscle has to increase over time relative to what you have already adapted to. That is why the same meta-analysis found 60% of one-rep max maximal for untrained lifters and 80% for trained ones — the target moves as you do. It does not specify weight in particular; load, repetitions and total weekly sets are all ways of raising demand.
Can I make progress without adding weight?
Yes, and there is a direct trial on it. Forty-three trained lifters spent eight weeks either adding load at constant reps or adding reps at constant load. Rectus femoris growth modestly favoured the repetition group and dynamic strength slightly favoured the load group, both to a degree the authors called of questionable practical significance. Both are viable; use whichever the week allows.
How many sets per muscle per week should I do?
More is generally better up to a point, and the point is not sharply defined. Each additional weekly set was associated with a 0.37% greater gain in muscle size in one meta-regression, but when sets were grouped into bands the effect was only a trend. A separate meta-analysis found four sets per muscle group per session maximal for both trained and untrained lifters. Somewhere in that range, done consistently, is the answer.
Does more volume always mean more muscle?
No, and the data is more cautious than the internet is. The continuous analysis showed a graded dose-response for weekly sets, but the categorical analysis of under 5, 5 to 9, and 10 or more sets per muscle only reached a trend at P = 0.074. Volume you cannot recover from is volume you do not adapt to, so treat the dose-response as a direction rather than an instruction to keep adding.
Do I need to train harder or just more consistently?
Consistently, in almost every case we see. The variables that moved strength in the meta-analysis were intensity relative to your level, frequency and set count — all of which are properties of what you do across months, not of how much any single set hurts. A logged, unglamorous programme that keeps beating its own numbers will outrun a punishing one you abandon in six weeks.
Sources
- Rhea MR, Alvar BA, Burkett LN, Ball SD. A meta-analysis to determine the dose response for strength development. Med Sci Sports Exerc, 2003. View study
- Schoenfeld BJ, Ogborn D, Krieger JW. Dose-response relationship between weekly resistance training volume and increases in muscle mass: A systematic review and meta-analysis. J Sports Sci, 2017. View study
- Plotkin D, Coleman M, Van Every D, et al. Progressive overload without progressing load? The effects of load or repetition progression on muscular adaptations. PeerJ, 2022. View study
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