move a muscle v. phr. To move even a very little.
■ Used in negative sentences and questions and with "if".
The deer stood without moving a muscle until the hunter was gone. The girls were so startled that they did not move a muscle. You're sitting right where you were when I left! Have you moved a muscle? The robber said he would shoot the bank worker if he moved a muscle. [TahlilGaran] English Idioms Dictionary ▲