I am currently getting ART treatments for a shoulder injury... couldn't even cast ... very tragic. What I have found so far is that as he works around the shoulder, a new scar tissue location is found each time. Meaning there was an original injury and then all the muscles tried to cover for it and then themselves became injured. BTW, that's in laymans terms.
After 7 treatments, he is now working on my bicep and I won't lie, it hurts. In fact, it kind of makes want to puke when he does it and I dread each visit a little more than the first. I even commented to him at my last thing that if I could reach around with my left, I probably would have popped him a few sessions ago. I always thought I had a pretty high pain tolerance but this stuff does not feel good at all.
Having said all of that, each part he has worked on has gotten better and the pain has definitely moved around the shoulder, so I have to assume it is working. I go for two more on the bicep, plus an ultrasound to see if there is anything more serious going on. After that, I will have a more definite opinion on this stuff.
But for now, if you read about a chiropractor getting popped while doing active release therapy on some guys shoulder, it was probably me.