A balance board is a device used as a circus skill, for recreation, balance training, athletic training, brain development, therapy, musical training and other kinds of personal development. It is a lever similar to a see-saw that the user usually stands on, usually with the left and right foot at opposite ends of the board. The user's body must stay balanced enough to keep the board's edges from touching the ground and to keep from falling off the board. A different challenge is presented by each of the five basic types of balance boards and their subtypes. Some of them can be attempted successfully by three-year-olds and elderly people, and some, because of their steepness and speed, are difficult and dangerous for professional athletes. In their design, what differentiates the five types (and their subtypes) is how unstable each of them is, i.e., in how many and in which of the three dimensions of space each board turns and/or sways and how freely its fulcrum contacts the board and the ground. Uses and users In 1953, Stanley Washburn Jr. filed a patent for a balance board with the intention of its use for recreation. These boards quickly become popular for skiers and surfers to practice their balancing skills in the off season or when natural conditions were poor. The balance board is a device that has come to be used for training in sports and martial arts, for physical fitness and for non-athletic purposes that are listed here. It is used to develop balance, motor coordination skills, weight distribution and core strength; to prepare people, before and after they reach old age, to avoid injurious falls; to prevent sports injuries, especially to the ankle and knee; and for rehabilitation after injuries to several parts of the body. Uses of a balance board beyond its athletic origin have become more common: to expand neural networks that enable the left and right hemispheres of the brain to communicate with each other, thereby increasing its efficiency; to develop sensory integration and cognitive skills in children with developmental disorders; to make dancers lighter on their feet; to teach singers optimal posture for the control of air-flow; to teach musicians how to hold their instrument; to shake off writer's block and other inhibitors of creativity; as an accessory to yoga and as a form of yoga, cultivating holistic health, self-awareness and calm. Some people use