The leg is composed of five distinct sections: upper leg, knee, lower leg, ankle, and foot.

The upper leg begins at the hip and continues down to the knee. The only bone in this region is the femur, the largest bone in the body. The femur’s head creates the ball of the ball-and-socket-style hip joint. The base of the femur makes up part of the knee.

The major muscles in the upper leg are the hamstrings and quadriceps. The hamstrings are three muscles at the back of the thigh that affect hip and knee movement. The quadriceps—the strongest and leanest muscles in the body—are a four-muscle group at the front of the thigh that work to extend the knee and lower leg. 

The knee is a pivot-like hinge joint in the leg that connects the bones in the upper and lower leg. It is the largest joint in the human body. The knee is where the femur in the upper leg meets with the tibia and fibula bones in the lower leg. Another bone, the patella or kneecap, is at the center of the knee.

The knee joint is composed of numerous tendons, ligaments, and protective elements, such as cartilage and bursa. These connective and protective tissues keep the bones in place and prevent them from grinding against each other while allowing the knee joint to flex and twist slightly.

The lower leg contains two bones. The tibia is the second largest bone in the leg. It meets the femur to create the knee. The fibula, the other bone in the lower leg, is connected to the tibia below the knee joint.

There are about 20 muscles in the lower leg. These do everything from helping to raise the lower leg to wiggling the toes. Many muscles that power foot movements begin as high up as the back of the knee and extend down to the foot.

Possibly the most important structure in the lower leg is the Achilles tendon. It connects three muscles—the plantaris, calf, and soleus—to the heel bone. It stores the elastic energy needed for running, jumping, and other physical activity.

The ankle is where the tibia and fibula meet the foot. Containing seven bones and numerous other structures, the ankle rotates and flexes the foot, which is important for movement and balance.

The foot is a complex structure made of more than 26 bones and 33 joints at the lowest portion of the leg. The structure of the foot is similar to that of the hand, but because the foot bears more weight, it is stronger yet less moveable.