This is a practice note for Tai-chi enthusiasts only. In this post I shall explain the inner mechanism and training objective of the 7th styles of Yin-section of 24 styles Tai-chi Nei Gung (reference material: Tai-chi Nei Gung by Wang DiXian (汪棣賢：太極拳内功). To serve the objective of practice improvement, the argument of who invented the styles and what is the definitive interpretation of the practice is irreverent, as far as I'm concerned.
The style is called "Left and Right whips" 左右揚鞭. Its training objective is referred to, in Wang's book, as "Strike with one's wrist like a whip" 手腕擊鞭。 No further explanation offered on top of basic movements with supporting photos. I'm filling in the training gap here (note: I was never trained under Wang, and not related to him in any way, though he has earned my warmest respect in disclosing the forms).
The objective of this style is to condition one's front torso, from the inside. Using Taoist terminology, it is to train up or strengthen one's Ren Mai (任脈). Ren Mai goes all the way connecting, with chi, one's tongue (which should be stretched with force through touching one's upper palette) and the center of one's pelvic floor muscles, for all convenience can be defined singularly as one's perineum (會陰), again with subtle force there. In chi-mechanics, chi will only flow through (at least) two stretched or focused points.
In doing microcosmic circulation, one directs one chi up one's Du Mai (督脈) or spinal cord and down the Ren Mai in front. In Style seven of 24 styles, the chi flows in reverse. Under the guidance of one's palm (always stretched), chi is made to flow upwards. However, unlike microcosmic circulation, chi is not allowed to go through one's head (which is done in reverse anyway). Instead chi will be forced to dissipate outside one's body, through the whipping action of one's hand and wrist. And in the whipping movement, one's energized Ren Mai will be further stretched, for conditioning or strengthening.
The above is my training notes. Needless to say, like everything else, practice at your own risk...:):)