To stretch the muscles which attach to the outside of the elbow and the hand which help to extent the hand (the wrists and fingers).
Stand next to a chair. Lean forward and place your outstretched hand on top of the chair's sitting surface with the back of the hand facing and in contact with the surface of the chair. The palm will be facing upwards.
In a slow and progressive manner push the wrist against the chair's surface until you feel the resistance of the end of range. At end of range, hold the position for 15 seconds whilst breathing slowly and deeply. Ensure you keep the elbow fully extended throughout the exercise.
If you suffer from connective tissue disease like rheumatoid arthritis ensure that you discuss this exercise with your osteopath.