People who build the most muscle from weight training show increased activity in their muscle cells’ systems that rebuild proteins, use energy during exercise, and fix damaged proteins.

Lifting weights helps people build bigger, stronger muscles, probably because it makes their muscles produce more protein and release helpful signaling molecules that help them grow and work better.

People who build some muscle with more training (but not a lot) show reduced activity in systems that break down muscle and increased activity in systems that help move proteins around and respond to hormones.

When you first start lifting weights, your muscles get tiny tears — and the protein your body makes right after working out is mostly used to fix those tears, not to make your muscles bigger yet.

Even lifting light weights, as long as you push until you can't do another rep, can build muscle just as well as lifting heavy weights in people who already train regularly.

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.