Start lying on your back, have an assistant with you to help with the exercise.
Start with your affected arm across your chest, elbow bent and hand on your opposite shoulder.
Bring your arm away from your opposite shoulder, keeping the palm down.
Finish with your arm pointing downwards by your hip on the same side.
Your assistant should provide graded resistance to slow the movement, but not to stop it completely.
If you do not have anyone to support you, you could use a wrist or hand weight.
