I've been feeling pain in the back of my shoulder joints pretty much every day after boxing for the past 2 weeks. Tonight, after punching a little harder and hitting the bag a bit longer than usual, the back of my right shoulder feels "strained". Is this normal for a beginner? It reminds me of the pain i used to get in all my other muscles when i first started lifting weights. Just take it easy and wait for the shoulder joints to adapt to the new activity you think?