The pronator quadratus is stretched with supination of the forearm at the radioulnar joints. Although not shown in this figure, the elbow joint should be flexed so that the pronator teres is slackened and knocked out of the stretch.
Note: The pronator teres is colored in here; not the pronator quadratus. As shown, this stretch position in this figure is ideal for the pronator teres, not the pronator quadratus. The elbow joint should be flexed for this to be the ideal stretch position for the pronator quadratus.