A specific type of weight training makes leg muscles grow unevenly, with some parts growing much more than others, because different parts of the muscle get worked harder during the exercise.

When untrained men do a specific type of weight training called pre-exhaustion, some parts of their thigh muscles grow more than others—the lower front part grows 44% thicker and the upper outer part grows 32% thicker.

Muscles don’t grow evenly—when you train your thigh, the top and middle parts of the front muscle grow more than the bottom, and the side muscle grows the same everywhere.

When performing resistance training, training to muscle failure may lead to slightly more growth in the vastus lateralis muscle, while training with 1-2 reps left in reserve may lead to slightly more growth in the rectus femoris muscle.

Different muscles in the front of the thigh may respond differently to how close to failure you train: the vastus lateralis may grow more when trained to complete fatigue, while the rectus femoris may grow more when trained with a few reps left in reserve.

Doing leg extensions with drop sets (going to failure, then lowering the weight and going again) makes the front part of your thigh muscle grow more than doing regular sets, but only in the upper and middle parts—not the bottom or the side muscles.