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[edit] Suwari Waza: 座り技
Techniques executed with both uke and nage in a seated position. These techniques have their historical origin (in part) in the practice of requiring all samurai to sit and move about on their knees while in the presence of a daimyo (feudal lord). In theory, this made it more difficult for anyone to attack the daimyo. But this was also a position in which one received guests (not all of whom were always trustworthy). In contemporary aikido, suwari waza is important for learning to use one's hips and legs.
Also, see SHIKKO.