Before revision: Structure The user stands on a board or other platform which is on top of an unstable ground-contacting member, the fulcrum.
After revision: Structure 255 px|The roller and underside of a rocker-roller boardVideo of a wobble board's instabilityThe underside of a sphere-and-ring boardThe user stands on a board or other platform which is on top of an unstable ground-contacting member, the fulcrum.