When you lift weights, your muscles grow bigger because your body makes more tiny protein-making machines inside muscle cells, which helps build more of the proteins that make muscles strong and bulky.

When you lift weights, your muscles make more of the tiny molecular machines that build proteins, which helps them grow bigger.

When you first start lifting weights, your body makes more of the tiny machines that build muscle proteins, which helps your muscles grow. But after a while, your body shifts focus and gets better at using those machines more efficiently instead of making more of them.

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.

When you lift weights, your muscles grow bigger because your cells first make more protein-making machines (ribosomes) — and the more of these machines you build, the more your muscles grow.