The fulcrum of almost all wobble boards is a semi-sphere or smaller spherical cap (or a shape that is approximately such) whose flat side is attached to the center of the board's underside. This allows the board to pivot in all directions, through 360 degrees. Standing on a wobble board exercises muscles that are not exercised by standing on boards that tilt in only two (opposite) directions. In almost all models, the board's length and width are about the same size; a circle is the usual shape.