Abstract: In a gas spring having a cylinder and a piston rod movable within the cylinder, braking elements are provided which brake or block the movement of the piston rod with respect to the cylinder when the interior pressure within the cylinder is reduced below a predetermined pressure. So the risk is eliminated that the piston rod when under load is unintentionally moved into the cylinder with a high velocity when the gas pressure within the cylinder is lowered below the predetermined pressure. The braking elements are spring loaded and are held in an inoperative position by adequate pressure within the cylinder.