If a guy does leg workouts with just one leg, three times a week for two months using heavy weights, that one leg gets noticeably bigger in muscle size—especially the fast-twitch fibers—while the other leg stays the same.

Lifting weights (3 sets of 8 reps at 80% of your max) three times a week for six weeks can increase the thickness of thigh muscles in young men who haven't trained before by about 2.9%.

Lifting heavy weights at least twice a week, doing full movements for a few sets each time, and doing it early in your workout can help healthy adults get stronger compared to not exercising or doing other types of training.

Whether you train both legs together or one at a time, your thigh muscles grow about the same amount after 12 weeks of heavy lifting.

You don’t need to train every day—just twice a week for two months can make your upper and middle thighs bigger, as long as you do enough total work.

If you lift weights twice a week for 8 weeks and do the same total amount of work, your upper and middle thighs will get thicker — no matter what fancy technique you use.