A walker or walking frame is a tool for disabled or elderly people who need additional support to maintain balance or stability while walking. The basic design consists of a lightweight frame that is about waist high, approximately 12 inches (30 cm) deep and slightly wider than the user. Walkers are also available in other sizes such as pediatric (for children) or bariatric (for obese persons). Modern walkers are height adjustable and should be set at a height that is comfortable for the user, but will allow the user to maintain a slight bend in their arms. This bend is needed to allow for proper blood circulation through the arms as the walker is used. The front two legs of the walker may or may not have wheels attached, depending on the strength and abilities of the person using it. It is also common to see caster wheels or glides on the back legs of a walker with wheels on the front.