This is a
common name for the positioning of the
hands prior to executing certain hand techniques in
Tae Kwon Do and other
martial arts. The correct wrist rotation will optimize the student's power when she executes a
block or a
strike, and can
render an opposing blow
useless, or a larger opponent
unconcious.
For instance, the Tae Kwon Do form Dan-Gun features a walking series of rising blocks. From a right-foot-back walking stance, the student places her right fist just forward of her hip, knuckles up. She then brings her left forearm across her body and parallel to the ground, and turn her left fist so that the knuckles are turned down and the backs of her wrists are touching each other. With her hands positioned thus, she is ready to execute the rising block by forcefully bringing her forearm from its position across her abdomen to just over her head, as if to block an overhead blow. The wrist rotation brings power to the technique by focusing the student's attention on the geometric arc of her forearm as it moves from her body to an attacker's wrist, rather than allowing her to fling her arm ineffectually at an incoming baseball bat. The opposing movement of her off-hand as it moves backwards to her hip and rotates from knuckles-up to knuckles-down complements the block itself, by focusing the student's strength into her blocking arm, and her sense of balance into her torso.
Alternatively, wrist rotation can be defined as the rotation the wrist offers when a student executes most basic punches. As the student's fist moves from its starting position, it will often rotate from knuckles-right (or left) to knuckles-up. It is commonly believed that rotating the fist produces more power when the student punches, not unlike the rotation of a bullet or a drill bit. While that may be true, it seems more likely that the rotation helps the student time when she should tense her forearm; such tension being a critical element in deciding whether the student breaks her wrist or ruptures an opponent's liver.