Proper extension of the arm, especially in the context of issuing power (fa jin), requires coordinated, inverse action between the shoulder and the elbow. As the elbow opens, the shoulder must be actively drawn in — that is, moved away from the point of contact. The opening action in the elbow is not the basic biomechancial action of opening a lid (i.e. increasing the angle between the upper and lower arm). Rather, it is a complete release of any isometric or other tension in and around the joint.

This definition of opening (i.e. release) is true for any joint while used in the act of issuing power (fa jin) and not to be confused with the opening of the joints required to create elastic structure (peng).