Not an injury as such, but on 3 of my recent solo runs I've had a really sore pain sort of underneath my left shoulder blade, and it feels muscular. A bit like my muscle is cramping or spasming. It's so sore it makes me stop running and I have to walk and stretch out my arm. Bringing my arm across the front of my body and holding it seems to help. The pain then goes away, but tends to happen once or twice again over the course of the run.
It's happened near the end of a 12 mile run, and twice at halfway through 6 mile runs, so it's happened in long slow runs and short fast runs.