If you're already used to lifting weights, whether you use free weights or machines, you'll gain about the same amount of muscle in your thighs, chest, and abs after 8 weeks — the type of equipment doesn't make a meaningful difference.

If you're already used to lifting weights, using free weights like dumbbells or barbells gives you about the same muscle growth in your thighs, chest, and abs as using weight machines — after 8 weeks of training.

This study only looked at the front and side of the thigh—so we don’t know if doing more sets helps your front thigh or hamstrings grow more.

Even if you do a lot of leg workouts, your thigh muscles grow about the same amount whether you do 20 or 50 sets a week—just doing any consistent training makes them bigger.

After nine weeks of lifting weights—whether heavy or light—men who work out casually don’t get bigger pectoral muscles, even though other muscles in their body do grow. This might mean some muscles just don’t respond the same way, or maybe they’re not doing the exercises right.

Doing a lot more leg workouts—over 50 sets a week—doesn’t make your thigh muscles grow bigger than doing 20–40 sets a week, even if you train for 12 weeks.