According to the tradition of the Yang family’s Taiji boxing was taught by master Huang Jinghua (a student of Yang Chengfu), it can be categorized into three levels of form training: heaven (high), human (middle) and earth (low) called San Pan. Although it performs in three levels of hight, middle, and low but the essence of the training is not on big/small or high/low of the external shapes but on Nei Gong training and its objective. Taiji Quan training first starts from the earth level or low frame, Nei Gong is on Tu-Na (breathing) of the lower part, the source of Jin is on Yong Quan point. Second is the man level or middle frame, Nei Gong focuses on Dan Tian internal turning, the source of Jin is on Ming Men point. Then another level is the heaven level or high frame, Nei Gong focuses on the opening of San Guan (three gates), the source of Jin is on Jia Ji point.
“Yang Taiji is One Family Across the Straits” by Qu Shijing.”杨氏太极两岸一家 – 瞿世镜”