About 20 years ago I went to a Dr that was a sports medicine orthopedic surgeon. Had his own practice, and was the head Dr. for the university orthopedic sports medicine dept. Dealt with many collegiate and pro athletes. I had 2 rotator muscles reattached. As well as a ruptured biceps taken care of.The Dr said it would be 18 months till the were fully graphed back on. Originally he said 3 months till I should start lifting with that arm. But he said to keep training the rest of the body. And training the good arm would keep the injured one from from atrophying as much and would keep the nerves functioning as well. Backs up what I had read else were. 5 days after the surgery back in the gym. Only doing rehab work for the injured shoulder along with stretching several times a day. 8 week s later the Dr said I could start training the repaired arm(as he knew I was doing some stuff anyway) as I was healing much faster then normal. 8 months later back to full power but I didn't push it ever work out for awhile till I felt confident. wish I had done it sooner.