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 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.

People who get much stronger from weight training tend to make more of the cellular machinery (ribosomes) that helps build muscle, while those who don’t get as strong show little to no change in this machinery.

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.

Lifting weights makes your muscles bigger and stronger, and this happens because your muscle cells start making more of the tiny machines that build proteins.

When guys who don’t lift regularly do weight training, even doing more sets doesn’t change certain key muscle signals called Akt and mTOR—so those signals must already be maxed out at low workout levels, and something else is driving the bigger changes seen in other muscle signals.