The Achilles tendon is actually a fibrous tissue that connects the calf muscle mass to the heel bone. It causes swelling and stiffness while in the back of the heel. There is frequently pain while in the Achilles tendon insertion into the calcaneus (heel bone) posteriorly (guiding). The Achilles tendon https://www.theorthopaedicandpainpractice.com/why-does-the-back-of-my-heel-hurt/