The apparatus (10) has segments (14a-14f) adjustable in relation to one another by actuators (16a-16f). An operating instrument (18) has an electronic control unit (22), which is connected to an operating face (20), a store (24) and the actuators via signal lines (28). A diagrammatic image of a human body is located in a portion of the operating face, where buttons are located on left and right of the image for an input of body-related adjustment commands. A button is located at the lower end of the operating face for selecting one of operating modes in which the apparatus is operated.