The Achilles tendon is the largest tendon in the human body. It is located at the back of the ankle joint and can be felt as a large, cord-like structure attaching to the back of the foot. Since tendons serve to attach muscles to bone, the Achilles tendon also attaches the large calf muscles, the gastrocnemius and soleus, to the back of the heel bone, the calcaneus.
The muscle mass and strength of the gastrocnemius and soleus muscles are greater than all of the other muscles of the lower leg combined. Therefore, the pull of these muscles on the Achilles tendon is very large since these muscles help balance the body while standing, push the body forward during walking, spring the body forward during running, and spring the body upward during jumping. Because of the large amount of stress which the Achilles tendon is subjected to during running and jumping activities, the Achilles tendon is prone to injury.