When guys who don’t normally lift weights do a tough leg workout on an empty stomach, their muscles show a big spike in two specific signals that tell the body to build more muscle, and this might mean doing more sets makes those signals even stronger.

If untrained guys lift weights on an empty stomach, doing 5 sets of exercise really ramps up a key muscle-building signal in their cells—but just 1 set doesn’t do much, suggesting you need more than a little effort to kickstart muscle growth.

When you lift weights, your muscles temporarily stop building protein, but right after you finish, they kick into high gear to repair and grow—this happens because key signaling molecules in your muscles get activated during recovery.

When you lift weights, a specific system in your muscle cells gets activated and tells your body to build more muscle protein, making your muscles bigger and stronger.

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.

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.