The evidence-led answer
NST verdict
There is no reliable percentage in these sources for how much of your own muscle growth is genetic. The strength heritability review concerns differences between people, not the share of an individual's training gains caused by genes [Zempo 2017]. Training responses vary, and the cited research discusses biological contributors without providing a personal prediction [Timmons 2011]. A slow response is not proof that training is pointless or that someone is doing something wrong.
How much is genetics?
The review estimated heritability of strength-related traits at 0.52 across 24 articles, with substantial variation between studies [Zempo 2017]. This is a population estimate, not a split of your gains into genetic and effort-based shares. It addresses strength-related traits in the studied populations, not a direct estimate of muscle growth after a programme. The age association does not show that effort inevitably becomes more important for every individual over time. The study does not isolate how much training, diet or sleep accounts for any person's result.
Are some people non-responders?
Measured training responses vary. That does not by itself tell us which differences are genetic or whether someone would respond differently to another programme [Timmons 2011]. Davidsen and colleagues examined high and low muscle-mass responders selected from 56 young men after 12 weeks of training. Differences in some microRNA responses were associated with muscle gains [Davidsen 2011]. Gene expression is not the same as an inherited DNA difference, and this association is not a test that can predict your potential.
What this means in practice
Compare your progress with your own starting point rather than treating a training partner as your expected outcome. A training log can help you review consistency and whether your programme remains manageable. If progress is unclear, review the plan and how you are measuring change. Do not automatically add more volume or train harder because an article labels you a slow responder. These sources cannot identify the cause of an individual's plateau, and a plateau is not evidence of laziness or poor genetics.
Limitations and uncertainty
Strength heritability is not the heritability of muscle growth in response to training. Estimates depend on the studied population, measures and environment. The review's age association does not establish the cause of an individual's progress or lack of it. The cited adaptation research is older, and the molecular study is small and specific. Gene-expression associations do not establish genetic causation or a validated individual prediction. This correction uses the published abstracts, not a full-text appraisal. Newer evidence and methodological issues in classifying responders remain to be reviewed.
Practical meaning
Compare your progress with your own starting point rather than treating a training partner as your expected outcome. A training log can help you review consistency and whether your programme remains manageable. If progress is unclear, review the plan and how you are measuring change. Do not automatically add more volume or train harder because an article labels you a slow responder. These sources cannot identify the cause of an individual's plateau, and a plateau is not evidence of laziness or poor genetics.
Limitations and uncertainty
Strength heritability is not the heritability of muscle growth in response to training. Estimates depend on the studied population, measures and environment. The review's age association does not establish the cause of an individual's progress or lack of it. The cited adaptation research is older, and the molecular study is small and specific. Gene-expression associations do not establish genetic causation or a validated individual prediction. This correction uses the published abstracts, not a full-text appraisal. Newer evidence and methodological issues in classifying responders remain to be reviewed.
