If you lift the same total amount of weight each week, it doesn’t matter if you spread it out over 5 days or do it all in 1–2 days — you’ll get the same strength and muscle gains.

If you spread your workouts over more days each week but keep the total work the same, you'll get stronger—but your muscles won't necessarily grow bigger.

If you're already experienced with weightlifting, doing full-body workouts every day gives you the same muscle and strength gains as doing different muscle groups on different days, as long as you do the same total amount of work each week.

If you're a guy who's been lifting weights for a while, working out each muscle four times a week doesn’t make you stronger than doing it twice a week—as long as you're doing the same total amount of work.

Untrained young men who perform resistance training twice a week for eight weeks at moderate intensity show measurable increases in maximal strength for the bench press, bent-over row, and back squat, with strength gains ranging from 20% to 40%, regardless of how the sets are organized.

Lifting weights more often each week helps you build bigger muscles and get stronger, but after a certain point, you don’t gain much extra strength—though your muscles can still grow. If you keep the same total amount of lifting, doing it in more frequent, lighter sessions helps strength more than muscle size.