Stand up straight with your back to the pulley.
Hold the handles in each hand with your affected arm straight by your side.
Your other hand will be just above you.
Pull on the pulley with your unaffected hand.
This will draw your other arm straight back behind you.
Go as far as you can manage comfortably, ensuring you do not lean your body or hunch your shoulders.
Hold this position.
Relax, and return to the starting position.