Yes, relative to where they start. When women and men follow the same resistance training program, their muscles grow by a similar percentage; men gain slightly more in absolute terms because they start with more muscle43.
So "as fast" depends on how you count. Measured as a share of the starting size, the sexes are close to level. Measured in raw size, men pull slightly ahead.
What was studied
Two meta-analyses answer this question directly. A meta-analysis is a study that combines the results of many earlier studies into one estimate. Both included only studies that put women and men on the same resistance training program (lifting against a load that rises as you get stronger), so the training itself was not the difference34.
- 2020 analysis. Young to middle-aged adults. It pooled 10 studies on hypertrophy (muscle growth), 17 on upper-body strength and 23 on lower-body strength. The protocol was registered in advance, which limits cherry-picking3.
- 2025 analysis. Healthy adults aged 18 to 45, 29 studies and 68 muscle-size outcomes, with a mean age of 26 in both sexes. Programs lasted about 6 to 24 weeks. It asked the question two ways: absolute change and relative change4.
Two terms matter here. An effect size is a change expressed on a common scale, so studies that measured in different ways can be pooled. Absolute change is the raw increase in size; relative change is that increase as a percentage of where each person started.
| What | 2020 analysis | 2025 analysis |
|---|---|---|
| Studies on muscle size | 10 | 29 |
| Ages | young to middle-aged | 18 to 45 (mean 26) |
| Also measured | upper- and lower-body strength | absolute vs relative size |
| Access here | abstract | full text |
In plain terms: the fairest comparison possible outside one giant trial, the same program for both sexes, pooled across dozens of studies.
What the studies found
Muscle size, relative: level. In the 2025 analysis, the relative gain in muscle size differed by 0.69% between the sexes, with a 95% credible interval from −1.50% to 2.88%4. A credible interval is the Bayesian cousin of a confidence interval: the range the true value most likely sits in. This one spans zero, so there is no clear difference. The authors conclude that women have a similar potential for muscle growth as men, "particularly when considering relative increases in muscle size"4.
Muscle size, absolute: men slightly ahead. The same analysis found a 100% probability that men gained more in absolute terms, but the size of that edge was small: a standardised mean difference of 0.19 (0.11 to 0.28)4. The authors describe the range as negligible to small. Muscle size differed between the sexes at baseline, which helps explain why raw and relative results diverge4.
The 2020 analysis agrees on size. Across 10 studies, muscle growth showed no significant difference between the sexes (effect size 0.07, P = 0.31), and the studies agreed with each other closely3.
Relative muscle growth, men vs women on the same program · % difference
Strength: women ahead in the upper body. In 17 studies, relative upper-body strength rose more in women (effect size −0.60, P = 0.002; negative favours women). In 23 studies on the lower body, there was no significant difference (−0.21, P = 0.20)3. The authors suggest untrained women may have more room to gain upper-body strength, and could not say whether the reason is neural, muscular, motor learning, or an artefact of short studies3.
Sex difference in training response (effect size; negative favours women) · ES
In plain terms: on the same program, women's muscles grow by about the same percentage as men's, and women's upper-body strength rises faster relative to where it starts.
The largest single study
One multi-centre study trained the non-dominant arm of 585 adults (342 women, 243 men) for 12 weeks and measured the biceps by MRI1. Men's relative gains in muscle size were 2.5% greater, which the authors called "only a slight advantage". Women's relative strength gains were considerably larger1. The spread between people dwarfed the difference between the sexes: size changes ran from −2% to +59%1.
A pooled analysis of 287 untrained adults aged 19 to 78 found the same pattern. Muscle size responses varied widely, and neither sex nor age changed the average response2.
What this does and does not mean
- Same principles apply. The trials gave women and men the same programs and saw similar relative results. Nothing here points to a separate rulebook for women; progressive overload works the same way (see what progressive overload is).
- Absolute size still differs. Men start with more muscle, so the same percentage adds more raw size. That is a statement about starting points, not about how well women respond.
- Individual spread beats sex differences. Two women on the same program can differ far more than the average woman and man1.
- Short studies. Most programs ran weeks to months. Whether the picture holds over years of training is not known.
- Cycle and life stage. These analyses did not test training by menstrual phase or after menopause. For the cycle question, see training around your menstrual cycle.
For how fast growth appears in the first weeks, see how long it takes to build muscle.
The studies at a glance
| Study | Who was studied | Key result | Year |
|---|---|---|---|
| Hubal et al., *Med Sci Sports Exerc*1 | 585 adults (342 women), 12 weeks of arm training | Men's relative size gains 2.5% greater; women's relative strength gains larger | 2005 |
| Ahtiainen et al., *Age*2 | 287 untrained adults aged 19–78 | Sex and age did not affect size or strength responses | 2016 |
| Roberts, Nuckols, Krieger, *J Strength Cond Res*3 | Meta-analysis, young to middle-aged adults | No size difference (10 studies); women larger upper-body strength gains (17 studies) | 2020 |
| Refalo et al., *PeerJ*4 | Meta-analysis of 29 studies, adults 18–45 | Relative size gains similar (0.69%); absolute slightly favours men (SMD 0.19) | 2025 |
Limits worth knowing
- Young adults. Both meta-analyses covered young to middle-aged adults; the 2025 mean age was 264.
- Mostly untrained. In 2025, only 6 of 29 studies involved participants with some training experience4.
- Short programs. About 6 to 24 weeks in the 2025 analysis; the 2020 authors raise short duration as a possible explanation for the strength result3.
- Overlapping authors. One author appears on both meta-analyses. The 2025 analysis reports no funding and declares that three authors work as coaches and writers in the fitness industry4.
- Abstract only for three. We read the 2025 analysis in full; the 2020 analysis, the 2005 study and the 2016 pooled analysis we read as abstracts.
Latest research
The newest study we opened is the 2025 Bayesian meta-analysis4. Its contribution is splitting absolute from relative change in one analysis. Relative growth was similar. Absolute growth slightly favoured men. Training experience did not change either answer, and type 2 (fast) fibre growth was similar between the sexes; type 1 (slow) fibre growth, and absolute growth in the upper body, slightly favoured men. It strengthens the 2020 conclusion rather than overturning it.
The short version
- On the same program, women's muscles grew by about the same percentage as men's.
- Men gained slightly more raw size, mainly because they start with more muscle.
- Women's relative upper-body strength rose faster; lower-body strength gains were similar.
- Individual differences were far larger than the difference between the sexes.
Educational overview only — not medical advice.
