I'd definitely start incorporating some warmups. Doran Yates goes over one that drastically helped me with the same problem. I can't remember the name, but you basically go to an arm curl machine and set it all the way up near shoulder height. You take a simple 10-15 pound weight and rotate it from horizontal to vertical. It doesn't work your shoulder out but it really gets your rotator cup warmed up and prevents injury. I do them before every workout that involves some sort of shoulders. Within a couple weeks I wasn't having any pain at all. Just go really light and do about 3 sets of 20. Do not work them heavy like a normal wormout, it's just to warm things up.
Lol they're hard to explain but check out Doran Yates blood and guts workout videos. It's on the very first part of this video,
Watch "Dorian Yates' Blood & Guts Trainer: Chest & Bicep…" on YouTube
Dorian Yates' Blood & Guts Trainer: Chest & Bicep…:
Dorian Yates' Blood & Guts Trainer: Chest & Biceps - Bodybuilding.com - YouTube
Check out some of his other stuff too. Dorian had a great career with hardly any injuries and is one of the few that still have amazing shape after everything he put himself through. So I think his injury prevention techniques are golden.
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