I broke my arm skateboarding down a monster hill on a homemade skateboard when I was 14. It was a hill I had skated many times but there was a section that required slowing down, a section with increased steepness and a sharp turn. I was late on my way to school and just didn't slow on this particular day until it was a little late. I slid for a distance on the inside of my elbows and my huge brass beltbuckle--both were shreaded. I know what you're thinking, "knarly dude."
But it wasn't very bad. A little disinfectant to keep the exposed elbow bones from getting infected and I would have been fine. Unfortunately I went to see a doctor, more to get out of school than because I felt I needed anything. Even though I didn't need it, the doctor put a cast on me for two weeks because he thought it would discourage me from skateboarding. It didn't. But it did mess up my shoulder because I was in the middle of a growth spurt.
So skip ahead to age 23. I'm doing 6-8 hours a day of Martial arts and Dance and I figure my biggest problem is that my shoulders are stiff and a little uneven. I get to work trying everything under the sun and moon. The first thing I figured out was that I needed to sleep with a shirt on because my shoulders would get cold at night and the muscles would tighten up over night. Without keeping them warm at night any progress I made in loosening them would be reversed by the cold.
Next I did a thousand experiments with bodywork and massage. About 3 hours a week for 4 years. I think this was positive at first but over the long term I simply learned more about how my own body relaxes than the people who were working on me. Now I almost never get bodywork.
At the same time I started creating tools to help me stretch. I had poles, staffs, ropes, bungee, a range of rubber balls from small to big to roll on, lots of eye-bolts in the walls with loops hanging from them, slanted boards, I even modified a door frame so it would be a better jig for me to stretch in. I was very disciplined. My housemates were very accommodating. I think they liked it that visitors to the house asked if our living room was a torture chamber.
The results, nada, nothing, waste of time. Stretching the shoulders doesn't work.
What does work? Slow qigong movements. Expanding and condensing from the dantian. Arm circles. Making sure your qi gates are open, that circulation is optimised, and that your alignment is efficiant.