The Smith machine is a piece of equipment used in weight training. It consists of a barbell that is fixed within steel rails, allowing only vertical movement. New variations allow a small amount of forward and backward movement. A Smith machine often includes a weight rack in the base to help stabilise it. Some Smith machines have the barbell counterbalanced. A power cage (also known as a power rack, squat cage or squat rack) is an item of weight training equipment designed to allow for a free-weight workout using a barbell without the movement restrictions imposed by equipment such as the Smith machine. It essentially comprises four vertical posts with two movable horizontal bar catchers on each side.