My physio told me to try and strengthen them, but I don't think I can get my lower trapezius to work. I'm wondering if its possible I damaged it? If you damage a muscle and it gets left for a while does the pain just go away and it doesn't function properly? - I'll give the dips and reverse shrugs a try when I next go to the gym.

I can do a 20 x 20kg barbell incline shoulder raise with 10s holds and not get tired. So would this imply that the muscle is strong? Or is it possible I use incorrect technique?

The first time I fixed my arm problem I felt a releasing feeling in my back and it felt as though I could feel my mid/lower traps come back into action. The next day I visited a chiropractor (I had booked the appointment prior to being fixed so I thought I should honor it), she tried to crack my back and the next day I woke up with a lot of pain in my mid back (around where the lower traps is). Is it possible this could have damaged the muscle? or strained it?