From Longman Dictionary of Contemporary Englishnot move a musclenot move a muscleNOT MOVINGto stay completely stillThe soldier stood without moving a muscle. →muscle
Examples from the Corpus
not move a muscle• I didn't dare move a muscle. He would have shot me.• I was so scared, I couldn't move a muscle.• The performers didn't move a muscle.• She hidbehind the door, not moving a muscle.• It suddenly occurred to them that he had not moved a muscle since they came in.• They will not move a muscle for at least another month or two.