Some people grow muscles easily everywhere, while others grow them slowly no matter what they do — it’s mostly about their body’s natural response.
Evidence from Studies
Supporting (4)
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Even when people did the same workout, some muscles grew differently — which means your body’s natural biology, not just how hard you train, plays a big role in how you respond to exercise.
Muscle Transcriptional Networks Linked to Resistance Exercise Training Hypertrophic Response Heterogeneity.
People’s muscles grow differently after weight training not just because of how they train, but mostly because of their natural, pre-existing biology—like their genes and how their muscles are already set up.
Resistance training load does not determine resistance training-induced hypertrophy across upper and lower limbs in healthy young males.
Even when people lift different weights, their muscles grow at similar rates compared to their own other muscles—meaning your body’s natural biology, not how you train, mostly determines how much you grow.
Molecular signatures underlying heterogenous hypertrophy responsiveness to resistance training in older men and women: a within-subject design.
Even when people do the same workout, some gain muscle and others don’t—and this study shows it’s because of differences in their bodies’ internal biology, not just how hard they trained.
Contradicting (1)
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This study found that how much you train and what you eat mostly determines muscle growth, not your body’s natural biology — so it doesn’t support the idea that your genes or internal biology are a big reason why people respond differently to workouts.