There are four main muscle groups in the thighs. The quadriceps on the front of the thigh, the biceps femoris on the back of the thigh, the leg adductors on the inner side of the thigh, the leg abductors on the outer side of the thigh. There are several other smaller muscles as well, but they will be completely developed if you focus on working the four main thigh muscle groups.
The quadriceps muscle has four lobes, and it primarily is used to straighten the leg from a bent position. This muscle is often called the “quads”. A secondary function of the quads is thigh adduction and rotation of the thigh within the hip socket.
The bicep femoris (also know as the hamstrings or leg biceps) consists of two lobes, and it primarily is used to bend the leg from a straight position.
The adductor and abductor muscles of the thighs help to pull your leg either toward the centre line of your body (adduction) or away from the centre line of the body (abduction).
The gluteus (also know as the “glutes”) form your buttocks. This large muscle is primarily used to extend the leg into a straight line with the torso and to rotate leg at the hip.