The Achilles is a commonly injured tendon. Many Achilles tendon injuries are caused by overuse, which leads to a swollen and painful tendinitis. In the most severe Achilles tendon injuries, too much force on the tendon can cause a partial tendon tear. In the worst cases, a complete Achilles tendon rupture results . There is a wide range of symptoms  that you may experience when you injure your Achilles tendon, from a weakness in your leg, to hearing an audible pop followed by leg pain.