PNF Backstroke from the Upper Body Opening series
My left shoulder has been a problem for me for a long time. When I was young it was very hypermobile, what some people would call "double jointed". I could make the shoulder joint move without moving anything else. I'm also pretty sure when I had my car accident the shoulder was injured along with my neck and spine. It's a frequent source of pain. This exercise has been helping alot lately.