A movable platform assembly comprises a base portion, able to be fixed to a support structure, and at least one pivotable arm hinged at one end with the base portion, about a first hinging axis, and at the other end with a loading platform, about a second hinging axis, the pivotable arm being able to be rotated by means of actuating devices, which are designed to allow the platform to maintain a constant inclination with respect to the base portion during rotation of the pivotable arm. The actuating devices comprise a first and a second rotary actuator mounted on the first and second hinging axis, respectively. The first rotary actuator comprises a first part fastened to the base portion and a second part rotatable with respect to the first part and fastened to the pivotable arm, and the second rotary actuator comprising a first part fastened to the loading platform and a second part rotatable with respect to the first part and fastened to the pivotable arm, said actuating devices also comprising control devices able to control in a co-ordinated manner rotation of said first and second rotary actuators.