If young guys lift weights in a structured way for 10 weeks, eat about 1.8 grams of protein per kilo of body weight every day, and have supervision, they can get way stronger—adding around 80–85 kg...

If young guys who already lift weights do intense leg workouts every day for two weeks, they get about 6% stronger in their leg press, showing their muscles and nerves adapt quickly.

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 female college athletes who already lift weights add a specific workout plan and eat 24 grams of protein before and after each session, they’ll get way stronger in their legs—adding about 90 kg to their leg press max in just eight weeks.

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're already strong and lift weights regularly, doing 10–15 hard sets per muscle group each week for 2 months will make you stronger and add a little muscle — whether you train your whole body every day or just once a week.