Introduction
The after-contraction is an old parlor trick of children which has been described many times as having interesting physiological and psychiatric implications. Although it is a difficult phenomenon to describe, it is easy enough to demonstrate. It is usually performed by abducting the stiffened arm against an immovable object, such as a table or wall. The appropriate muscles of the shoulders are contracted isometrically without movement; the subject is then requested to relax and to step away from the restraining object. In most cases the arm will then involuntarily “float up” into the air toward the horizontal position with a floating sensation.This involuntary movement, which is a continuation of the originally intended movement, usually persists for 10 to 15 seconds. It may be demonstrated in almost any muscle group of the body, including the muscles of the hand, leg, or eye. It is ap