The back remains peng to protect the back. The front peng protects the front. Back and front peng occur together. Arms push out connecteding the chest with peng.
Peng on the outside equals connections on the inside. Connection creates full energy.
When the left side has peng it is easier for the right side to have peng. When one side does not have peng it is easier for the other to not have peng.
When the left arm is peng it extends and connects the joints so that there is no blockage in the elbow or the hand. When there is no blockage in the joints then contact takes place with the dantien with looseness, connection and peng.
Even peng is 360 degrees.