A mechanical device that performs single, orthogonal, alternate, and independent movements which, adapted in an apparatus, can be applied to the prevention of lower limb thrombosis suffered by people who spend long hours in a sitting position. The device includes a solid cylinder shaped as a horizontal axis with a solid, centered, and jointly-moving sphere with grooves on its surface, along which runs a guiding bolt that guides the movement all along the grooves. The guiding bolt is joined to one of the arms of a fork-shaped piece. On the other arm of the fork, there is a ball-holding cavity with a spring to push a ball into a depression on the sphere surface opposite to the grooves. The guiding grooves engraved on the piece, which are read by the guiding bolt, are transferred to the pedals adhered to the gym apparatus.