It can endure great force, but it is still susceptible to injury. Achilles tendonitis is either acute or chronic: Acute symptoms. Achilles tendonitis symptoms & diagnosis. Achilles tendinitis is a common condition that causes pain along the back of the leg near the heel. Acute Achilles tendonitis symptoms develop gradually over a few days. You will feel pain and stiffness in the Achilles tendon at the back of the ankle. It is particularly painful first thing in the mornings, or after a period of rest. It connects your calf muscles to your heel bone and is used when you walk, run, and jump. For Achilles tendonitis and tendonosis, shoe orthotics can be used to correct foot misalignments (if, for example, flat feet, are believed to be causing or contributing to Achilles tendon pain). Achilles tendonitis occurs when the tendon that attaches the calf muscles to the heel becomes painful or inflamed. For anyone with Achilles tendonitis or tendonosis, heel lift orthotics can unload stress on the tendon and ease pain. The Achilles tendon is the largest tendon in the body. The Achilles tendon is the largest tendon in the body.