Muscles of the Thigh and Lower Limb (Leg)
Muscles of the thigh and lower limb (leg) tend to be large and heavy because they are used to move the entire weight of the body and to resist the force of gravity. Therefore, they are important for movement and balance.
Muscles That Move the Thigh 
Iliopsoas (includes psoas major and iliacus) originates from the ilium and the bodies of the lumbar vertebrae, and inserts on the femur anteriorly. This muscle flexes the thigh (raises the leg anteriorly) and is important to the process of walking. (The term leg is used in this section and the next to refer to the entire lower limb.)
It also helps prevent the trunk from falling backward when a person is standing erect.
Gluteus maximus is the largest muscle in the body and covers a large part of the buttock (gluteus means buttocks in Greek). It originates at the ilium and sacrum, and inserts on the femur. The gluteus maximus acts to straighten the leg at the hip (and, in that way, to extend the thigh) when a person is walking, climbing stairs, or jumping from a crouched position.
The iliopsoas and the gluteus maxim us are antagonistic muscles because the iliopsoas flexes the thigh. and the gluteus maxim us extends it.
Gluteus medius lies partly behind the gluteus max­imus. It runs between the ilium and the femur, and functions to abduct the thigh (raise the leg sideways to a horizontal position).
Adductor muscles (pectineus, adductor longus, adduc­tor magnus, gracilis) are located on the medial part of the thigh. They originate from the pubic bone and is­chium, and insert on the femur. Adductor muscles adduct the thigh (bring the leg down from a horizontal position) and press the thighs together.
The gluteus medius and adductor muscles are antagonistic because the gluteus medius acts to abduct the thigh. and the adductor muscles act to adduct it.
Muscles That Move the Lovver Limb (Leg) 
Quadriceps femoris group (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) includes muscles found in the front and on the sides of the thigh. The rectus femoris, which originates from the ilium, lies in front of the vastus intermedius. The vastus muscles originate from the femur. The vastus muscles are the primary extensors of the lower leg, such as when a ball is kicked.
Hamstring group (biceps femoris, semimembranosus, semitendinosus) is composed of several muscles found at the back of the thigh. They all have origins on the ischium and insert on the tibia. Their strong tendons can be felt behind the knee. These same tendons are present in hogs and were used by butchers as strings to hang up hams for smoking-hence, the name. The hamstrings help flex the lower leg and extend the hip.
The quadriceps femoris group of muscles and the hamstring group are antagonistic because the quadriceps femoris group extends the lower leg, and the hamstring group flexes it.
Sartorius is a long, straplike muscle that begins at the iliac spine and then passes inward across the front of the thigh to descend over the medial side of the knee. It flexes the leg and is used to sit cross-legged, as tailors were accustomed to do in another era. Therefore, it is sometimes called the tailor's muscle, and, in fact, sartor means tailor in Latin.
Muscles That Move the Ankle and Foot 
Gastrocnemius is located on the back of the leg, where it forms a large part of the calf. It arises from the femur; distally, the muscle joins the strong Achilles tendon, which attaches behind the calcaneus bone (heel). The gastrocnemius is a powerful plantar flexor of the foot that aids in pushing the body forward during walking or running. It is sometimes called the toe dancer's mus­cle because it allows a person to stand on tiptoe.
Tibialis anterior is a long, spindle-shaped muscle located on the front of the lower leg. It arises from the surface of the tibia and attaches to the bones of the ankle and foot. Contraction of this muscle causes dorsiflexion and inversion of the foot.
The gastrocnemius and the tibialis anterior are antagonistic muscles because the gastrocnemius brings about plantar flexion. and the tibialis anterior dorsiflexion, of the foot.
Peroneus muscles (peroneus longus, peroneus brevis) are found on the lateral side of the leg, connecting the fibula to the metatarsal bones of the foot. These muscles evert the foot and also help bring about plantar flexion.
Flexor and extensor digitorum longus muscles are found on the lateral and posterior portion of the leg. They arise mostly from the tibia and insert on the toes. They flex and extend the toes, and assist in other move­ments of the feet.