The Achilles tendon is the largest tendon within the body, it attaches the calf muscles to the heel bone. It is a very powerful structure that load up to 12-13 times the bodies weight during running.
It is crucial for walking and running as during the propulsive (toe off) phase of gait (walking) as the calf muscles contract (tighten) to drive the body forward the Achilles tendons pulls on its attachment site, the heel bone, to create heel lift and ankle joint movement.