The Achilles tendon is the largest tendon in the human body and can withstand forces of 1,000 pounds or more. But it also the most frequently ruptured tendon.
Both professional and weekend athletes can suffer from Achilles tendonitis, a common overuse injury and inflammation of the tendon. Events that can cause Achilles tendonitis may include: hill running or stair climbing, overuse resulting from the natural lack of flexibility in the calf muscles, rapidly increasing mileage or speed, starting up too quickly after a layoff and trauma caused by sudden and/or hard contraction of the calf muscles when putting out extra effort such as in a final sprint.
Achilles tendonitis often begins with mild pain after exercise or running that gradually worsens. Other symptoms include: recurring localized pain, sometimes severe, along the tendon during or a few hours after running, morning tenderness about an inch and a half above the point where the Achilles tendon is attached to the heel bone, sluggishness in your leg, mild or severe swelling, and stiffness that generally diminishes as the tendon warms up with use.
In extreme cases, surgery is performed to remove the fibrous tissue and repair any tears.