I gave myself rotator cuff and biceps tendonitis training to do human flags:
(not me in the pic)
Took forever to heal. I took every supplement that supposedly benefited tendonitis, did ice massage multiple times a day, weighted eccentric rehab exercises, etc. The healing process isn't linear. There will be no change (in pain level) for weeks at a time and then one day you wake up and it's a little better, and then it will stay at that level for weeks and then one day you wake up and it's a little better, etc.
I couldn't do squats during that time, either, because I couldn't hold the bar in place without getting into a painful shoulder position.
My goal was to do a human flag on each side but I'm afraid to ever try it again.
The bizarre thing is I wasn't even doing it often. I would attempt it one time on each side once or twice each week. You hear tendonitis and think "overuse injury." Not always.
I grabbed the bar one day with my left hand on the bottom, went to position myself in place, and felt a pain in my shoulder.
Both the PT and the joint specialist pressed into my shoulder and said they could feel the inflammation in my biceps tendon, and the shoulder pain I was having sounded like microtears in the rotator cuff.
I'm starting back very slow at the gym. To put things in perspective, before the injury I was doing flat DB press with 100s for reps. Now I am doing 15s and 20s, for 10 reps, slowly through the entire ROM just to make sure there is absolutely no pain or discomfort whatsoever.
After each workout is a shoulder ice massage.
An ice massage is when you freeze water in a styrofoam cup and then peel the top of the cup off, holding it by the bottom, and massage the area with the ice. It works 100x better than an ice pack, which does next to nothing in my opinion.
I'm going to slowly increase the weight by 5 pounds every week or every workout until I get back up to 50 pound dumbbells (my old warmup weight). Then I will consider myself at a relatively good starting place.