Lie on your side with your knees bent.
Hold a dumbbell in your uppermost hand with your elbow tucked into your side and a towel between your elbow and your side.
Your elbow should be bent with your hand pointing up towards the ceiling and with your palm facing forward.
When ready, keep your elbow in place and slowly lower the weight down towards the floor in front of you.
Your assistant can then change the weight you are holding, before you lift the weight back to the starting position.
Then, change the weight again and repeat.