The fibularis (peroneus) longus depresses the base of the first metatarsal, allowing the body to advance forward, over the limb that is in contact with the ground (the stance limb).

Vastus medialis is most medial (medialis) as well as most distal. Rectus femoris is located most medially to the leg, but not the body, which is what is used as reference when looking at anatomical position. Vastus lateralis (lateral) and Vastus medialis (medial) are also not correct as they do not fit the description of both medical and distal. Finally the sartorius is not part of the quadriceps muscle group.

The tibialis anterior and extensor digitorum longus muscles both dorsiflex the foot at the ankle joint; the tibialis anterior also inverts the foot at the intertarsal joints and the extensor digitorum longus extends the proximal and distal phalanges. The gastrocnemius and soleus muscles are plantarflexors of the foot at the ankle joint. The gastrocnemius also flexes the leg at the knee joint.

The iliopsoas muscle is composed of the iliacus and psoas major muscles. It functions as a flexor of the thigh at the hip joint and laterally rotates it. It's also capable of flexing the trunk on the hip as in sitting up from the supine position.

The long head of the biceps femoris attaches to the ischial tuberosity, and has attachments to the sacrotuberous ligament. Through this attachment, it is thought that the long head of the biceps femoris helps stabilize the sacroiliac joint. Although the gluteus maximus attaches to the sacrotuberous ligament, the gluteus medius does not, and neither do the gemellus superior nor the adductor magnus.

Although the gastrocnemius is a large muscle, it is not as involved in walking and running as is the soleus. Rather, it is a powerful plantarflexor of the foot and is more active in jumping and other movements that require powerful plantarflexion. The gracilis muscle is located in the thigh, and is responsible for weak flexion, internal rotation, and adduction of the hip. The plantaris muscle only minimally aids in running and walking and is not present in about 10% of the population. This means the correct answer is the soleus muscle.

The biceps femoris muscle forms part of the hamstrings, and consists of a long and short head. Both heads perform knee flexion, and the long head is involved in hip extension as it originates in the pelvis.

Quadratus femoris is a strong external rotator and adductor of the thigh. Piriformis is a lateral rotator, and laterally rotates the femur, abducting it, during hip extension. The quadriceps consist of rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. The quadriceps flex the hip and extend the knee.

The soleus is one part of the calf muscle, and is deep to the gastrocnemius. This muscle inserts via the achilles tendon to the calcaneus and allows for plantarflexion of the foot.

The tibial tuberosity is located at the proximal anterior portion of the tibia, and the navicular tuberosity and 1st cuniform are located in the midfoot and are insertion points for medial and lateral muscles of the foot and lower leg.

The quadriceps femoris group of muscles are the main extensors of the leg at the knee joint. They consist of the rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis muscles. The rectus femoris muscle also flexes the thigh at the hip joint.

The semitendinosus, gracilis, and sartorius are the three muscles that make up the pes anserine group, coming from the posterior, medial, and anterior compartments of the thigh, respectively. The adductor longus, is not part of this group as it inserts on the linea aspera of the femur, rather than the pes anserinus, like the semitendinosus, gracilis, and sartorius.