When you lift weights or do resistance training, your muscles get bigger — and one big reason is that your body turns on a molecular switch (mTORC1) that tells your muscles to make more protein, though other things are also helping out.

When you lift weights, your muscles turn on a specific molecular switch called mTORC1, which helps build more muscle protein. But just because this switch flips on right after a workout doesn’t mean you’ll definitely get bigger muscles over time—it doesn’t always line up.

Lifting weights makes your muscles bigger, mostly because it turns on a special signal in your muscle cells that tells them to make more protein, but other things might help too.

When you lift heavy weights, your muscles grow bigger because your body turns on a special chemical signal (mTORC1) that helps make more muscle proteins and building tools, letting your muscles grow faster.

When you lift heavy weights, your muscles get stretched and stressed just enough to tell your body to build more muscle fibers—this happens because a special molecular switch (mTORC1) turns on, making your muscles produce more proteins and the machinery needed to make them.

Lifting weights makes your muscles bigger and stronger because it turns on a cellular switch (mTORC1) that tells your body to build more muscle proteins.