If the tendon continues to be used, microtears occur which heal with scar tissue which is not as elastic nor is it as strong as the original tissue. As the injury becomes chronic, adhesions begin to develop between the tendon sheath and the tendon which can permanently change the anatomy of the area. The athlete may feel a crackling or grinding sensation while rubbing the tendon or while lightly pinching the tendon when the foot is moved up and down. The Achilles can withstand a force of 1000 pounds without tearing. Despite its tremendous strength, the Achilles tendon is the second most frequently ruptured tendon in the body.
Most ruptures occur about two to three inches from where the tendon inserts on the heel bone.
This area is the narrowest part of the tendon and has the poorest blood supply. The most common mechanism of injury is a quick and powerful toe off and flexion of the foot, as in sprinting. Often, the athlete will lose the ability to push off on the injured side. In a complete tear of the Achilles there will be a palpable defect in the tendon. The doctor will do a test where the patient's injured calf is squeezed.