I understand.KPj wrote:See, when I said 'impinge' or 'impingement zone', I didn't mean 'impingement syndrome'. It's actually quite a 'false' term.
I think I know what's happening. As I abduct my arm the biceps tendon is lying just under the edge of the acromion. If I have some loading on my arm, the biceps is at least stabilizing, so the tendon is taut. As I raise my arm, the humeral head comes up trapping ("impinging") the tendon against the acromion, not tightly enough to cause pain, but to tether it there. As I adduct, the tendon is released, allowing to snap out from under the acromion (since it is still under tension.
I'm thinking that this is a pretty valuable discovery, in that if I had continued doing the WG pull-ups and the lateral raises it would have started putting more pressure on the tendon, and could have caused trouble. I'll work on posture issues and shoulder retraction, depression first before doing these again.