A rest portion (3) is used to support a load at an adjustable height relative to a base (2) which is connected to the rest portion by a pivotal linkage (4). A hydraulic ram (13) coupled to a gas spring cylinder (72) applies a spring force between the linkage and the base, the geometry of the linkage and ram being such that the upward component of spring force is invariant with respect to height adjustment. A control valve (82) allows the ram to be locked at a selected height and the spring force provided by the gas spring is adjustable by movement of a second piston (40) within the gas spring cylinder to vary the available volume of gas. A hydraulic pump (77) is used to supply hydraulic fluid to the cylinder for adjusting movement of the second cylinder. The apparatus is suited for use in a chair-bed enabling a patient to be supported at an adjustable height during medical treatment.
