Remember your geometry?
Whenever A = B and B = C, then also A = C. Right?
Good, hold that thought.
It is an all too common occurrence that we are asked by our athletes how they might improve their shoulder flexibility so as to improve their overhead lifting capacities. When looking for increases in range and joint flexibility it is easiest to go after the most simple and most obvious impediments first. For example, most athletes that experience difficulty working overhead also have stiff thoracic spines. Duh, obviously Kelly. I don't know why you wasted your time on that stupid doctoral degree...
Bare with me.
Because these athletes have a stiff thoracic spine, they often also lack the ability to achieve good thoracic extension (as if you were laying back over the hood of a car and sticking your chest up in the air).
And, because they don't extend well, their shoulder blades literally have no place to go when they should be moving back and out of the way of the raising arm. Thoracic extension facilitates scapular retraction. Having your shoulder blades get out of the way of your arms effectively eliminates a potentially boney block to your dumbell squat snatch.
"So if she floats, she's made of wood, and she's a witch! Burn her!)
Whenever A = B and B = C, then also A = C
Work on your thoracic extension to improve your overhead badness.
Here's a little proven method to work on your transitive shoulder motion.
Get a couple of tennis balls and some athletic tape.
Tape the tennis balls together length wise.
Tape around the middle "waist" of the thoracic weapon.
Cross your arms over your chest and place the tennis balls anywhere along your rib cage.
Rock side to side and take big breathes until that segment no longer feels tight.
Moving one joint segment at a time, rock side to side and identify any areas that feel stiff. Plan on a 5 minute session.