The Achilles tendon is the largest and strongest tendon in the human body. It is formed by the union of the gastrocnemius and soleus muscles (the calf) and attaches to the calcaneus (heel bone). Despite its strength, it is subjected to forces up to several times a person’s body weight during running or jumping.
Achilles injuries occur when the demand placed on the tendon exceeds its structural capacity. This can happen through chronic wear-and-tear (degeneration) or a sudden, explosive force that tears the fibres. A unique characteristic of the Achilles tendon is a “watershed zone”—an area about 2 to 6 cm above the heel attachment—that has a relatively limited blood supply. This zone is where most injuries and ruptures occur, as reduced blood flow can slow the natural repair process.