The hamstring muscle group is responsible for knee flexion. The quadriceps muscle group is responsible for knee extension. The posterior muscle group is not an anatomical muscle group. The biceps muscle group is located in the upper arm, and produces elbow flexion.

The rectus femoris belongs to the quadriceps muscle group. The hamstring muscle group consists of: biceps femoris, which is located most lateral, and semimembranosus, and semitendinosus which is located most medially.

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 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 muscles that insert to the achilles tendon allow for plantarflexion of the foot, which is created due to shortening of the posterior muscles of the lower leg. Dorsiflexion is created through the anterior muscles of the lower leg. Eversion is created through the lateral muscles, and inversion is created with the medial muscles. Abduction is the motion of moving a body part away from the midline. 

The sartorius, semitendinous and gracilis all make up the pes anserine tendon. Vastus medialis, although on the medial aspect of the knee, does not make up this muscle group as it inserts to the tibial tubercle via the patellar tendon. 

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 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 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.  

In order to cause flexion or extension of a joint, a muscle must originate on one side of the joint and insert on the other. In other words, the muscle body must cross the joint in order to affect it.

The biceps brachii, brachialis, corocobrachialis, and brachioradialis originate from the scapula or humerus and insert on the radius or ulna. Each of these muscles thus crosses the elbow. In contrast, the flexor carpi radialis originates on the radius and inserts on the second metacarpal. When contracted, the flexor carpi radialis causes flexion of the hand at the wrist, but does not affect the position of the forearm.