The quads
Both. Concentric: Exercise where the muscle is contracted under a load Eccentric: Exercise where the muscle is stretched under a load. So when you squat down its eccentric, when you come back up its concentric. Most exercises are both, with a few exceptions (i.e. jumping of a wall is mainly eccentric, while a punch is mainly concentric. Eccentric contraction is associated with increased muscle growth, but also DOMS (Delayed onset muscle soreness, when your muscles are very sore after a workout).
isometric
Rapid stretching and contracting of muscles. Ex) squat jump, repeat squat jump.
Glutes and quads contract when you stand, lengthen when you squat. So it's eccentric for those muscles. There are a bunch of muscles involved in a squat, some may be concentric.
Both the deadlift and squat are important exercises for strength and muscle development. However, for optimal overall strength and muscle development, it is generally recommended that your deadlift should be higher than your squat. This is because the deadlift engages more muscle groups and requires greater overall strength compared to the squat.
The back squat primarily works the quadriceps, hamstrings, and glutes.
Squat.
Quad
mainly your legs but and your back a little
A back squat primarily works the quadriceps, hamstrings, glutes, and lower back muscles.
The back squat primarily works the quadriceps, hamstrings, glutes, and lower back muscles.
The barbell squat primarily works the quadriceps, hamstrings, glutes, and lower back muscles.