Stuck acromioclavicular joint?

I went to a physio and he said the AC was stuck,and the tendons were getting irrated by not having any give or movement in the shoulder. He gave me a couple of good whacks on the shoulder. Moved my shoulder around a bit, and said all fixed. Then he put the electrodes on for 10 minutes, showed me an exercise to do, and come back in a week. He said it was common, and should be ready to go in no time at all!
I have no idea how I did this, except I do weights at the gym on a regular basis. I began to notice a little discomfort when doing some shoulder and chest exercises, and thought I should check it out before it got worse.

cheers

The alignment and rotatory ability of the AC jt does at times get stuck. Does this might well be the case. To correct it longterm he/she will need to assess the way you are performing exercises in the gym (and don't do lat pulldowns behind the neck). Almost always you will need to get more thoracic extension mobility. :)

Thank you for your reply!