I can't stand seeing me get an injection! But I have several nurses and EMTs in my family who somehow manage to handle far worse things.

I've recently been having pain in my left shoulder and arm, from the top front of the shoulder down about halfway to the elbow. It started happening after I started using the suspension training system that I got for Christmas. I had similar pain a few years ago that was caused by something I was doing at the gym, though I can't remember now what was causing it. I've taken a break from the suspension training but noticed that the pain got worse again after doing incline dumbbell presses at the gym.

Then the other day I was using a lacrosse ball to work out some tightness in my upper back (leaning my back against a wall with the lacrosse ball in between and rolling it around). The ball hit a really tight painful spot just inside the left shoulder blade. After that, the pain in my shoulder and arm went away -- pain-free full range of motion. A few days later the pain came back, I used the lacrosse ball again, and the pain went away.

I've had a similar experience with a tight muscles inside my right shoulder blade causing neck pain on my right side.

Which is all a long way of saying -- it can be really hard to tell why something is hurting and how to address it. I tend to get lazy about general stretching and working on tightness with a foam roller and lacrosse (or tennis) ball, but it really can be helpful.