Abstract: A chair has an adjustable seat or back rest which is connected with an air spring. The air spring has an engaged condition in which the seat or back rest is locked, and a disengaged condition in which the seat or back rest may be adjusted as desired. A pivotable handle located beneath the seat permits a user to change the condition of the air spring. The handle is connected with a first shaft which carries a first coupling element. A second shaft carries a cooperating second coupling element and acts on an actuating rod of the air spring to change the condition of the latter in response to manipulation of the handle. The shafts are relatively rotatable, and the coupling elements define a gap permitting rotation of one coupling element relative to the other through a distance equalling the length of the working stroke of the actuating rod. In the engaged condition of the air spring, each coupling element is held in a respective end position by a biasing force. The handle is in a lower terminal position.