In Part 1 of this two part series, I discussed what I believe is the most common cause of shoulder pain. So, if the term "scapulohumeral rhythm" is not familiar to you, I suggest checking out that post before reading this one. Anyway, if the scapula does not move freely when you move your arm, something bad is going to happen (ever hear of impingement?)
You see, when your scapula is allowed to move through it's full ROM, then the muscles have ample space to do their work. If the scapula's ROM is limited, then that space gets closed off. I won't go further into all the technical details, but I will let you know some of the major contributors to poor scapular movement.
