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.

If you're a guy who's been lifting weights for a while, doing either 2 or 4 workouts per week for each muscle can boost your strength by about 8–11% in just 8 weeks—as long as you do the same total amount of work overall.

If you lift weights the same total amount each week, it doesn’t matter if you do it in one big session or split into three smaller ones—you’ll get just as strong and build just as much muscle.

If you're already strong and lift weights, training each muscle group either once or five times a week for eight weeks will give you about the same strength gains on the bench press, squat, and row.

If you do the same workout three times a week instead of once, and you end up doing more total weight lifted, you’ll get stronger and build more muscle—because you’re doing more work overall.

Lifting weights three times a week instead of two makes your muscles grow bigger, no matter what type of muscle fibers you have — but it doesn’t make you stronger in one-rep max lifts.