When young men who haven't trained before do one-arm exercises for eight weeks, their resting muscle building speed goes up by almost half in that arm, but the part that builds muscle fibers stays the same, showing different parts of muscle react differently to exercise.

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.

If you do lots of reps with lighter weights for six weeks, your body might make more of the non-muscle proteins inside your muscles than if you lift heavy weights with fewer reps — and this difference is pretty big.

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.

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.

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.