Abstract: The present invention involves a spline element for a seat in a vehicle, in which the height of the seat can be adjusted without changing the spline initial stress, and wherein the initial stress of the spline can be adjusted without making a change in the height of the seat. This is achieved by means of a cylinder which provides an enclosed gas compression compartment against which a pair of pistons disposed at opposite ends of the cylinder can be adjusted from each end thereof. Each piston has flow channels provided therethrough which can be closed with the aid of a respective back stroke valve which can be set in motion at any time from the outside, thereby turning the piston into a floating piston.