"Peng" produces protection of the self, the body, and supports chi flow. Each arm/hand controls one side of the body. When the arm/hand crosses the mid-line one loses peng, and loses control. The right arm/hand controls the right side of the body. And the left controls the left side of the body. Each hand controls its own side of the body. When the hand crosses the center line peng is lost and when there is no peng there is no protection.