I attended one beginner course in CFT Lauttasaari where they said that this is a common problem with guys and recommended stick/bar training to improve flexibility and range of motion. This is necessary for safe training for technical manoeuvres such as clean and jerk. I want to hear your opinion about this, I think inflexibility can be a serious flaw and all power training should be done so that it does not get worse. My goals are to get such flexibility that I can safely train basic weight-lifting movements and play tennis without compromising power (and still having the range of motion). I made a little video showing how bad the inflexibility is here.
Which muscles and which movements do I need to address the inflexibility problem with hands straight behind back?