Like ligaments, tendons are strong, but they are not particularly flexible. They will stretch only so far before they wear, tear or rupture. The exact cause of rupture of the Achilles tendon is not known. As with Achilles tendonitis, tight or weak calf muscles may contribute to the potential for a rupture. If this muscle is weak and becomes fatigued, it will tighten and shorten.
Overuse also causes muscle fatigue.
This tightness will increase the stress on the Achilles tendon. A rupture usually occurs when there is force on the tendon that is greater than the tensile strength of the tendon. Most ruptures occur from a combination of a forceful stretch of the tendon with a contraction of the calf muscles. A classic sign of an Achilles tendon rupture is an athlete looking over his shoulder to see who or what has just hit their ankle. Tendon Rupture A completely ruptured Achilles tendon will require surgical repair, followed with up to 12 weeks in a series of casts.