With the hand to be worked out in front of your body, fingers together and thumb pointing up. Hold the thumb to be stretched with your other hand and pull it towards the body and forearm as shown in the image. You should feel a stretch in the muscle in your hand that sits between your thumb and first finger.
Hold this position for the duration directed by your clinician. Repeat as many times as is indicated.
Do not pull the thumb too hard, the stretch should be strong but not painful. Make sure you keep your fingers together and away from the thumb, the bigger the distance between the thumb and fingers the stronger the stretch.