Most of what we know about how much to lift and how often comes from young men who already work out—so we don’t know if it works the same way for women, older people, or beginners.

When counting sets that work multiple muscles at once, giving them half credit (instead of full or zero) makes predictions about muscle growth and strength more accurate.

Training more often helps you get stronger, but doesn’t seem to help you get bigger muscles—so frequency matters more for strength than for size.

People who do strength training like lifting weights may live longer because studies show they’re less likely to die from any cause compared to those who don’t.