Muscles of the Hip
The muscles of the thigh and lower back work together to keep the hip stable, aligned and moving. It is the muscles of the hip that allow the movements of the hip:
flexion – bend
extension – straighten
abduction – leg move away from midline
adduction – leg moves back towards midline
external rotation (allows for the foot to point outwards)
internal rotation (allows for the foot to point inward)
The hip muscles are divided up into three basic groups based on their location: anterior muscles (front), posterior (back), and medial (inside). The muscles of the anterior thigh consist of the quadriceps (or quads): vastus medialis, intermedius, lateralis and rectus femoris muscles. The quads make up about 70% of the thigh’s muscle mass. The main functions of the quads are flexion (bending) of the hip and extension (straightening) of the knee.
The gluteal and hamstring muscles, as well as the external rotators of the hip are located in the buttocks and posterior thigh. The gluteal muscles consist of the gluteus maximum, gluteus medius, and gluteus minimus. The gluteus maximus is the main hip extensor and helps keep up the normal tone of the fascia lata or iliotibial (IT) band, which is the long, sheet-like tendon on the side of your thigh. It helps with motion of the hip, but perhaps more importantly, acts to help stabilize the knee joint.
Gluteus medius and minimus are the main abductors of the hip —that is, they move the leg away from the midline of the body (using the spine as a midline reference point). They also are the main internal rotators of the hip (i.e. turn the foot inwards). The gluteus medius and minimus are also important stabilizers of the hip joint and help to keep the pelvis level as we walk.
The tensor fascia lata (TFL) is another abductor of the hip, which, along with the gluteus maximus, attaches to the IT band. The IT band is a common cause of lateral (outside) hip, thigh, and knee pain.
The medial muscles of the hip are involved in the adduction of the leg i.e. bringing the leg back towards the midline. These muscles include the adductors (adductor magnus, adductor longus, adductor brevis, pectineus, gracilis). Obturator externus also helps to adduct the leg.
The external rotator muscles (piriformis, gemelli, obturator internus) of the hip are located in the buttock area and assist in lateral rotation of the hip (out-toeing). Lateral rotation is needed for crossing the legs.