When your muscles contract or get stretched, the physical pull they feel is the main reason they grow bigger — it's like the muscle gets a signal from the tugging to grow more muscle fibers.
Evidence from Studies
Supporting (4)
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Load-induced human skeletal muscle hypertrophy: Mechanisms, myths, and misconceptions
This study says lifting weights (which pulls and stretches muscles) is the main reason muscles grow bigger, and other things like muscle pump or hormones don’t really matter — which matches the claim perfectly.
This study says that when you lift weights, the pulling and squeezing of your muscles is the main thing that makes them grow bigger, and your body has special systems to sense that tension and turn it into muscle growth.
Load-induced human skeletal muscle hypertrophy: Mechanisms, myths, and misconceptions
This study says lifting weights (which pulls and stretches muscles) is the main reason muscles grow bigger, and other things like muscle pump or hormones don’t really matter — which matches exactly what the claim says.
When you lift weights, your muscles sense the pull and turn on a special growth switch (MAPK pathway) — this study proves that tension is what flips that switch to make muscles bigger.
Contradicting (1)
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Muscular and Systemic Correlates of Resistance Training-Induced Muscle Hypertrophy
The study looked at what happens inside muscles after weight training, but didn’t measure the actual pulling force from muscles — which the claim says is the main reason muscles grow. So we can’t say if that force is really the key driver.
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.