When untrained young men lift lighter weights until they're tired for 10 weeks, it changes how their fast-twitch muscle cells organize themselves to better support muscle growth.

Lifting weights until you're tired, whether with light or heavy weights, makes your muscles bigger and stronger in the same way for beginners.

When young guys who don't usually exercise lift weights until they're tired, it wakes up special muscle repair cells and helps build stronger muscles—no matter how heavy the weights are.

Lifting heavy weights three times a week for six weeks makes fast-twitch muscle fibers grow bigger by about 12% in people who don't usually exercise, showing it especially targets these powerful muscles.

Whether you lift heavy weights with fewer reps or light weights with more reps—as long as you push until you can’t do another rep—your muscles grow about the same amount.

Whether you lift heavy weights for fewer reps or light weights for more reps—as long as you push until you can’t do another rep—your muscles grow about the same amount.