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

蓄勁如張弓,發勁如放箭.

"Accumulate Jin like drawing a bow, emit Jin like releasing an arrow."

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.