polyurethane ball, is the fulcrum on which the board is balanced, and the fulcrum is kept contained under the board by a guard rail or ring on the underside. By redistributing his/her weight across the board, the rider can move the board in any direction– side to side, forward and backward, twisting, diagonal, and full rotations or any combination of these movements. A rider can move the board vertically by doing an advanced maneuver called an ollie. It can also be tilted in any direction and fully rotated. Sphere-and-ring boards provide the greatest freedom of movement of any type of balance board, allowing rotation about all axes (yawing, pitching and banking) and translation (i.e., sliding) in both transverse (i.e., lateral) and longitudinal directions. They, like wobble boards, simultaneously exercise muscles that are not exercised by use of boards that tilt about only one axis (in two opposite directions). When balancing or riding on a sphere-and-ring board, the difficulty and ride speed, which is how fast the rider can move the board on the ball, are determined by the following: Ring shape and size Larger rings allow more movement of the fulcrum. Different shapes change how the fulcrum might move. Sphere's size, weight, and rigidity These affect how fast the fulcrum moves and how much strength is required to move it. Board's shape and size Changing these can affect the weight and weight distribution of the board, changing how much strength is required to move it. Aquatic These are underwater balance boards. They were developed for physical therapy and are used also for recreation. Besides the general advantages of aquatic therapy over non-aquatic therapy (the use of the smooth resistance of water instead of the jerky resistance of weights and the avoidance of burdening an injured joint with excessive weight– in this case, the weight of the patient's own body), aquatic balance boards have the specific advantage over non-aquatic balance boards of saving a patient who slips off of a board from the impact of falling and crashing into a floor. Slipping off of an aquatic balance board is safe as long as the user knows to avoid inhaling while underwater and knows how to tread water. Three models are produced by Theraquatics Australia: The Theraquatics Balance Board is a V-shaped rocker board that a user stands, kneels or sits on. The Wonder Board is a V-shaped rocker board that a