To do this stretch the stretcher lies face up with their elbow, wrist and fingers fully stretched out with their palm facing down, then they should make a fist. If the stretcher makes a fist before extending their arm they will not reach the end of range point for the muscles being stretched that is required for optimal stretching. The partner should wrap their hand around the stretchers hand, matching finger to finger and thumb to thumb. The partners other hand should be stabilizing the stretchers wrist and forearm. The stretcher should then try and open their hand and extend their wrist, not forgetting to include the thumb. After this push the stretcher should inhale deeply and on the exhale contract their flexors to deepen the stretch.
Images from www.wikipedia.com