The majority of muscles in the leg are considered long muscles, in that they stretch great distances. As these muscles contract and relax, they move skeletal bones to create movement of the body. Smaller muscles help the larger muscles, stabilize joints, help rotate joints, and facilitate other fine-tuned movements.
The largest muscle masses in the leg are present in the thigh and the calf.
The muscles that make up the quadriceps are the strongest and leanest of all muscles in the body. These four muscles at the front of the thigh are the major extensors (help to extend the leg straight) of the knee. They are:
- Vastus lateralis: On the outside of the thigh, this is the largest of the quadriceps. It extends from the top of the femur to the kneecap, or patella.
- Vastus medialis: This teardrop-shaped muscle of the inner thigh attaches along the femur and down to the inner border of the kneecap.
- Vastus intermedius: Between the vastus medialis and the vastus lateralis at the front of the femur, it is the deepest of the quadriceps muscles.
- Rectus femoris: This muscle attaches to the kneecap. Of the quadriceps muscles, it has the least affect on flexion of the knee.
The hamstrings are three muscles at the back of the thigh that affect hip and knee movement. They begin under the gluteus maximus behind the hipbone and attach to the tibia at the knee. They are:
- Biceps femoris: This long muscle flexes the knee. It begins in the thigh area and extends to the head of the fibula near the knee.
- Semimembranosus: This long muscle extends from the pelvis to the tibia. It extends the thigh, flexes the knee, and helps rotate the tibia.
- Semitendinosus: This muscle also extends the thigh and flexes the knee.
The calf muscles are pivotal to movement of the ankle, foot, and toes. Some of the major muscles of the calf include:
- Gastrocnemius (calf muscle): One of the large muscles of the leg, it connects to the heel. It flexes and extends the foot, ankle, and knee.
- Soleus: This muscle extends from the back of the knee to the heel. It is important in walking and standing.
- Plantaris: This small, thin muscle is absent in about 10 percent of people. The gastrocnemius muscle supersedes its function.
Possibly the most important tendon in terms of mobility is the Achilles tendon. This important tendon in the back of the calf and ankle connects the plantaris, gastrocnemius, and soleus muscles to the heel bone. It stores the elastic energy needed for running, jumping, and other physical activity.