When older people do strength training and their muscles grow a lot, the muscle cells add more nuclei—and those who grow the most gain about 32% more nuclei than those who don’t grow much.

When older people do strength training, those who get the biggest muscle gains also tend to have a much bigger rise in a protein called c-Myc—some see it jump 250%, while others only see a 50% rise.

When you lift weights and your muscles get bigger, the number of special repair cells and nuclei inside them tends to go up a bit — but that’s not the whole story; other things are also helping your muscles grow.

Even though the muscles got bigger after the exercise, the number of special repair cells and nuclei inside the muscle fibers didn’t go up — meaning the growth happened without these typical building mechanisms.

Doing your workouts more often per week doesn’t seem to help you build more muscle, as long as the total amount of lifting stays the same.

When people lift weights, how much their muscles grow depends way more on their own body than on the type of workout they do—because even when people switch up their routines, their muscle growth stays pretty much the same.