A stationary exercise device includes a frame member having a transverse pivot axis. A first and a second foot tread member are operatively associated with a coupling member for pivotally coupling the first end of each foot tread member to the pivot axis at a predetermined distance from the pivot axis,...http://www.google.es/patents/US7033306?utm_source=gb-gplus-sharePatente US7033306 - Spontaneous symmetrical weight shifting device
