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When people lift weights regularly, their muscles usually get about 5% bigger on average, no matter what kind of weight routine they follow.

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Pro
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Against

Evidence from Studies

Supporting (2)

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Community contributions welcome

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Similar muscle hypertrophy following eight weeks of resistance training to momentary muscular failure or with repetitions-in-reserve in resistance-trained individuals

Randomized Controlled Trial
Human
2024 Jan

This study found that after 8 weeks of weight training, people’s thigh muscles grew by about 5%, no matter if they trained until exhaustion or stopped a little short — which matches the claim that 5% is a typical muscle growth rate from resistance training.

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Muscle hypertrophy and strength gains after resistance training with different volume matched loads: a systematic review and meta-analysis.

Systematic Review With Meta-Analysis
Human
2022 Apr

The study found that no matter how heavy or light the weights are, as long as you do the same total amount of work, your muscles grow about the same amount — which supports the idea that muscle growth from weight training usually hovers around 5%.

Contradicting (1)

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Community contributions welcome

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Molecular signatures underlying heterogenous hypertrophy responsiveness to resistance training in older men and women: a within-subject design.

Randomized Controlled Trial
Human
2025 Sep 1

This study found that some older people’s muscles barely grow from weight training, while others grow more — so saying everyone gains about 5% isn’t right; many gain much less or nothing at all.

Gold Standard Evidence Needed

According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.

Similar Assertions

If you're already fit and lift weights, doing 5 to 20 sets of exercises for each muscle group every week won't make you grow bigger muscles any more or less than any other number in that range.

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84%

Doing your workouts more often per week doesn’t seem to help you build more muscle, as long as the total amount of lifting stays the same.

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84%

When people who already work out build muscle, they don’t get much bigger very fast, and the gains slow down over time—so to tell if one workout plan is better than another, you’d need to study a lot of people.

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84%

If you want to get stronger, doing your workouts more often helps—more than if you just want to get bigger muscles.

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83%

If you lift light weights for more reps or heavy weights for fewer reps—but do the same total amount of work—you’ll grow your muscles just as much either way.

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