Excerpt from <span class="chinese-post-title">十三勢行功要解</span> the Important Explanations for the Accomplishment of the Thirteen Postures by <span class="chinese-post-title">武禹襄</span> Wǔ Yǔxiāng

發勁須沉著鬆淨,專注一方.立身須中正安舒支撐八面.

"In order to emit power (Jin), one must be calm, collected and relaxed, concentrated in a single direction. The standing body must be centered, straight and serene, so you one handle the eight directions."

By Wǔ Yǔxiāng (武禹襄), based on the translation by Yang Jwing Ming (楊俊敏) presented in the book Tai Chi Secrets of the Wu & Li Styles (太極拳武李氏先哲秘要) and various translations on the internet.