A manually operated seat height adjustment actuator mechanism includes a rotatory actuator-driven torque input mechanism defining a first axis and a torque output mechanism defining a second axis offset from the first axis. The rotatory actuator-driven torque input mechanism is provided by a planetary gear assembly. The torque output mechanism comprises a cycloidal drive assembly including eccentrically driven gears. Linking gearing operatively links the torque input mechanism and the torque output mechanism. The eccentrically driven gears engage an output pinion configured to engage a gear segment of a seat height adjustment mechanism for raising and lowering a seat.