Start in standing with your shoulder out to the side at 90 degrees, with your elbow also bent at 90 degrees.
Your hand should be by your ear.
Have your assistant place a force in a backwards direction against your hand while you try and push your hand forward.
After the designated period of time, move your hand slightly forward maintaining your shoulder and elbow at 90 degrees.
Have your assistant apply backwards pressure here again, and repeat this through your shoulders range of motion.
