The Achilles tendon is the largest tendon in the body. It connects the muscles in the lower leg (calf) to the heel bone. With every movement of the foot, the Achilles tendon stretches and tightens. Because it is under so much stress, it can partially or completely tear (rupture) from excess force or overuse. Ruptures usually occur about two inches above where the tendon attaches to the heel bone.
An Achilles tendon rupture is most common in middle-aged "weekend warriors" who are not conditioned for athletics and who neglect to properly warm up and stretch prior to exercise. Ruptures frequently occur from sudden movements that stress the calf muscles, such as jumping or quick stops; from overstretching; from vigorous exercise after a long period of inactivity; or from untreated Achilles tendinitis/tendinosis (overuse).