Not sure if I can explain this very well, but here goes.

I was doing shrugs on the machine with two handles and plates on the sides yesterday and before I let the weight down, I held it and let it stretch my right trap out a little. As I was doing that, I bent forward slightly to get a good stretch aDP took a deep breath. All of a sudden, it felt like all the muscles between my shoulder blades began spasming or something. It was hurting to breath at first and for the most part now, has went away. Any idea what that could have been? My running coach told me that you can strain the small muscles bewteen ribs so I thought maybe that was it????

You probably just pulled or strained something. I did the very same movement you did and something began to burn/hurt in my lower back. I dont mess around with that shrugs machine anymore cause my back hurt for a week after that.

Now when i use that machine i just lift the weight off the ground using my legs and lower it using my legs. I keep my back completely straight the entire time, no leaning foreward or back. I dont want to pull something again.