What is an Achilles heel?

The Achilles tendon is one of the longer tendons of the body, explains WebMD. The tendon stretches from the bones of the heel to the calf muscle and can be felt by touching the tendon at the back of the heel.

The Achilles tendon is a commonly injured tendon, according to WebMD. Achilles tendon injuries are caused through overuse, wearing high heels, flat feet or having muscles in the leg that are too tight. As a result, Achilles tendon injuries are frequent in sports such as running, gymnastics, dance, basketball and tennis. Symptoms of an Achilles tendon injury include tenderness, swelling, pain and difficulty flexing.