Pump-handle is a movement of the ribs that results in a change in the anteroposterior diameter of the thorax.
[1] One of the most important functions of the ribs and diaphragm is the change in volume of the thorax that helps inspiration and expiration.
[2] In general, the ribs move around two axes.
Movement at costovertebral joints 2 to 6 about a side-to-side axis results in raising and lowering the sternal end of the rib, the "pump-handle" movement.
In elevation, this increases the anteroposterior diameter of the thorax.