Lifting weights at a challenging level makes your muscles build more protein, and this boost happens just as much in arms or legs that are used to exercising as in ones that aren't.

People respond to weight training in wildly different ways—some grow muscles a lot, others hardly at all—and those differences between people are about 40 times bigger than the tiny differences you’d see if you trained one leg harder than the other in the same person.

When young men lift weights to build muscle, their muscle-building process speeds up at first but slows down after 10 weeks, even if they keep increasing the difficulty.

Your muscles make more protein at first when you start lifting weights, but after a few weeks, that boost fades—even if you keep lifting harder.

For men who exercise regularly, doing both weight training and intense cardio together doesn't slow down muscle building compared to just weight training alone, even after 10 weeks of working out.

When you start lifting weights, your muscles build new protein faster in the first week than they do after 10 weeks, even if you keep training.