San Ti Shi Elbows, Arm pit and Ribs

Up until now when I've done the San Ti Shi I've felt a big stretch in the back like I was getting rid of some of those fascia crosslinks and getting more mobility. Today when I was doing San Ti Shi I noticed though that the out reached hand side of the body could feel a closing of the ribs sensation when I was thinking about the elbow rotating inwards and the hand going forward. I also could noticed a connection through the arm pit area with the out stretched arm. I also felt like when I was doing this today it did start to feel like it was working my body in a more demanding way than before.