If you're a new guy to lifting weights, doing 3 sets of leg exercises 3 times a week for almost 3 months will get you way stronger than doing just 1 set — like 41% stronger versus 21%.

For men who already lift weights, doing either high-intensity or high-volume workouts for 8 weeks didn't make a big difference in leg strength or muscle size.

For young guys just starting out at the gym, doing 1 set or 3 sets of each exercise gives about the same strength boost in the upper body after 11 weeks.

If young guys who don’t work out start doing 3 sets of leg exercises instead of 1, they’ll get stronger legs and bigger thigh muscles—41% stronger and 11% more muscle—but their arms and chest won’t see the same extra benefit from doing more sets.

Lifting heavier weights for fewer reps makes your legs much stronger than lifting lighter weights for more reps, but both types of training help your upper body a little bit too, and this might work differently for different muscles.

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.