Wearing a cast on a broken leg can cause atrophy, or withering, in the leg, because it is immobilized and gets no exercise.
Appearing in English in the 17th century, the word atrophy originally described a lack of nourishment. Atrophy occurs in parts of the body that can't move or be "fed" because of disease or injury. It also is used to describe things that go dull through lack of use, like skills in sports or artistic creativity. The (unrelated) word "trophy" refers to something that sits on a shelf and is admired, while atrophy is a condition of being "shelved," or made inactive and lifeless.