Use barbell behind-the-neck squats to train the outer quadriceps, and use leg presses or shoulder-rest squats to train the rectus femoris and vastus medius. Additionally, to make the quadriceps angular, you must isolate it with seated kicks and scissor squats.
Barbell back squat
Focus on developing the inner quadriceps, using a squat machine or Smith frame squat are both good choices.
Action: Put the barbell on the back of the neck and shoulders and move it up and out, keeping the barbell balanced. Keeping your head upright, bend your knees and squat until your thighs are below the horizontal surface, and stand up to the starting position.
Points: It is critical that the thighs are below the horizontal plane when squatting, especially for beginners, otherwise they will use the force to extend the legs. If you don't squat low enough when you start, you'll be more susceptible to injury when you add weight later. The distance between the two feet is about shoulder width, in an "outer eight shape", with the toes facing outwards, so that the force on the inside is more concentrated and the practice is more accurate. When standing, the knees should not be pointed inward or outward to avoid excessive force on other parts of the body. When squatting, the direction of the knees should be toward the direction of the toes, and the barbell, hips, and feet should not be in a straight line. That is to say, the movement trajectory of the barbell should be consistent with the longitudinal axis of the human body, perpendicular to the ground, and smoothly straight down and up. Always look straight ahead when squatting and standing to avoid hunching over or leaning the weight of the barbell too far forward.