If you're already used to lifting weights, it doesn't really matter if you change up how heavy you lift, how many reps you do, or how long you rest—your muscles will grow about the same either way.

Lifting lighter weights might make your slow-twitch muscles grow more than your fast-twitch muscles, according to some new ideas.

If you're already used to lifting weights, mixing up your routine—like changing how heavy you lift, how many reps you do, or how long you rest—won't make your muscles grow any bigger than sticking to the same routine. Both ways work about 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.

Even when you train one leg differently from the other, both legs tend to grow muscle in similar ways — which means your body’s natural biology, not the workout itself, is what really controls muscle growth.

Lifting heavy weights might make your fast-twitch muscle fibers grow bigger than your slow-twitch ones, according to some new research.