A gas spring assembly that is displaceable between an extended condition and a compressed condition can include a first end member, a second end member, a flexible wall secured between the first and second end members, a spring chamber and a volume-displacing body disposed within the spring chamber. The body can be supported along one of the flexible wall and the first end member such that the body remains in spaced relation to at least the second end member in a compressed condition of the gas spring assembly. A method of adjusting a gas spring assembly is also included.