Well, my main question for you here is why the comment about fins preventing you from getting good body rotation with back stroke. I put in 45 minutes to an hour, daily, 4 to 5 days a week, just dedicated to kicking because that is the weakest part of my stroke. The young man here, does fine with body rotation while wearing the fins. I swim all of my kicking laps like I swim, so arms extending alternately, and 40 or so degrees of rotation. The fins do not inhibit, in any way my ability to rotate my body, either with back stroke flutter kick or freestyle flutter kick, So, why that comment? Have you actually tried it? Second point is the arm pull. Since I swim the old over arm side stroke, I see every thing in the pool. Strangest thing I see with the arm pull in back stroke, and all of the swimmers do it here, is at about half way through the pull, they rotate their palm over and the finish whip of the wrist goes straight to the bottom of the pool. The young man did worse in the before video, and better prior to his test. Since the pull is more horizontal, the fingers and palm should be pointing to the side of the pool for the entire pull, just like with freestyle, you keep your fingers pointed to the bottom of the pool. As soon as that palm starts to rotate sideways you are losing your grip on the water. His body position still needs work. From a coach at Speedo, "Suck in your gut like you are trying to put your belly button on your spine. That is the cause of the arched back, which is a normal reflex action for us bipeds when we lay down flat, arched back so the head can rise and see forward. His gut isn't any bigger than mine, but sucking it in will do wonders for getting him on the surface of the water.