 This technique is referred to in the forms of training school as the Lao Jia Chen Paochui (old frame, cannon fist, one of the two original forms Chen-style t'ai chi ch'uan), while in Yang school, especially for those who have a direct lineage to Yang Shaohou the fa jin is added to techniques to release the stored energy.A main principle in creating fajin, is using your dantian.The dantian is thought to be the storehouse of your energy and can be used in striking.