The Achilles tendon is the strongest tendon in the human body. Because most Achilles tendon injuries take place in sports and there has been a general increase in popularity of sporting activities, the number and incidence of the Achilles tendon overuse injuries and complete, spontaneous ruptures has increased in the industrialized countries during the last decades. The most common clinical diagnosis of Achilles overuse injuries is tendinopathy. The basic etiology of the Achilles tendinopathy is known to be multi-factorial. Although histopathologic studies have shown that ruptured Achilles tendons have clear degenerative changes before the rupture, many Achilles tendon ruptures take place suddenly without any preceding signs or symptoms.