If you do the same total amount of lifting, whether you lift heavy weights for fewer reps or lighter weights for more reps, you'll build about the same amount of muscle as a beginner.

If you lift heavy weights for fewer reps and lighter weights for more reps but do the same total work, you'll build about the same muscle size, but you'll get stronger faster with the heavy weights.

How many times you lift a weight affects what your body gets better at: lifting heavy weights a few times builds strength, lifting lighter weights many times builds endurance, and doing a middle amount builds muscle size.

When people lift weights in a way where they can do 12 reps max, getting stronger is closely tied to getting bigger muscles. But this link isn't seen when lifting for only 4 or 8 reps max.

If you do the same total amount of weightlifting work, lifting heavier weights fewer times or lighter weights more times gives men about the same muscle growth.

If you lift light weights for more reps or heavy weights for fewer reps—but do the same total amount of work—you’ll grow your muscles just as much either way.