The Achilles tendon of the lower extremity is subject to continued trauma with overuse due to excessive pronation (inward rotation of the foot on the leg). Achilles tendonitis has a characteristic cycle of great stiffness and pain in the morning after walking or jogging. Depending on the severity of injury, pain might be present at rest or after vigorous exercise. There may also be local swelling.
With Achilles tendonitis there is usually abnormal motion of the foot and much inward rolling. This causes pain, and muscles and tendons of the Achilles tendon to spasm as it tries to balance the foot. As a result, the tendon becomes inflamed from the tork of the imbalance.