I was climbing in a gym for only the 3rd time this year and decided I need to do a big endurance session. Being able to just get more routes in during a day at the crag is one of my goals for the next season. They had several auto-belays and the gym wasn't busy so I tried to see how many "ARC-style" laps I could do in a session. About an hour into it I developed sharp pain in my right shoulder. I did all the usual climber stretches, along with some self-massage on trigger points in the shoulder and forearm. The pain felt like when you really throw your arm/shoulder out in baseball if you didn't warm-up properly. Primarily localized in the rotator cuff area, but radiating down into the outer forearm too.
I was only doing very easy laps, and tried to focus on technique drills and pushing with my feet, all while not loading the right shoulder significantly. I kept climbing for approximately 2 more hours. The shoulder continued to hurt for about half of the time, but by the end of the session I was virtually pain free.
We shall see how it fares in the morning, but it was very odd. I've never had shoulder problems. I would love to keep it that way. Any ideas what it might be/have been?