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To sit seiza-style, one must first be kneeling on the floor, folding one's legs underneath one's thighs, while resting the buttocks on the heels. The ankles are turned outward as the tops of the feet are lowered so that, in a slight "V" shape, the tops of the feet are flat on the floor and big toes overlapped, the right always on top of the left, and the buttocks are finally lowered all the way down. Depending on the circumstances, the hands are folded modestly in the lap, or are placed palm down on the upper thighs with the fingers close together, or are placed on the floor next to the hips, with the knuckles rounded and touching the floor. The back is kept straight, though not unnaturally stiff. Traditionally, women sit with the knees together while men separate them slightly. Some martial arts, notably kendō, aikidō, and iaidō, may prescribe up to two fist widths of distance between the knees for men.
Stepping into and out of seiza is mindfully performed. There are codified traditional methods of entering and exiting the sitting position depending on occasion and type of clothing worn.
Through the early history of Japan, various ways of sitting were regarded as 'proper', such as sitting cross-legged, sitting with one knee raised, or sitting to the side. People's social circumstances, clothing styles, and the places where they sat naturally brought about their manners of sitting. The development, in the Muromachi period, of Japanese architecture in which the floors were completely covered with tatami (thick straw mats), combined with the strict formalities of the ruling warrior class for which this style of architecture was principally designed, heralded the adoption of the sitting posture known today as seiza as the respectful way to sit. However, it probably was not until around the years surrounding the turn of the 18th century (the Genroku to Kyōhō eras in Japanese history) that the Japanese generally adopted this manner of sitting in their everyday lives.
Seiza involves sitting down on the floor and not on a chair. In traditional Japanese architecture, floors in various rooms designed for comfort have tatami floors. Seiza thus is closely connected with tatami flooring. There are circumstances, however, when people sit seiza-style on carpeted and hardwood floors. In many martial arts, for instance, this sitting position generally takes place on hardwood floors. Depending on the formality of the occasion, the setting, and the relative status of the person, it is sometimes acceptable to sit on a special cushion called a zabuton (literally a "sitting futon").
Sometimes stools are provided for elderly or injured people even when others are expected to sit seiza-style. It is advisable, particularly in formal situations, to at least try to sit seiza-style. Non-Japanese who have not grown up sitting in this posture may, however, have difficulty assuming it at all. Those unfamiliar with seiza will likely find that maintaining it for more than a minute or two tends to lead to paresthesia, whereby the compression of the nerves causes a loss of their blood flow, with the accompanying 'pins and needles' feeling, followed by painful burning sensations, and then eventually complete numbness in the legs. However, the physical discomfort lessens with experience as the circulation of the blood improves. Experienced seiza practitioners can maintain the posture for forty minutes or more with minimal discomfort. Certain knee problems are made worse when assuming this position, specifically Osgood-Schlatter disease.
Special seiza stools are available in Japan. They are folding stools, small enough to be carried in a handbag, which are placed between the feet and on which one rests the buttocks when sitting seiza-style. They allow one to maintain the appearance of sitting seiza while discreetly taking pressure off the heels and feet.
Use in traditional arts
Doing seiza is an integral and required part of several traditional Japanese arts, such as certain Japanese martial arts and tea ceremony (a table-style version of tea ceremony known as ryūrei was invented in the 19th century). Seiza is also the traditional way of sitting while doing other arts such as shodō (calligraphy) and ikebana (flower arranging), though with the increasing use of western-style furniture it is not always necessary nowadays.
Walking on the feet and knees while in the seiza posture, known as shikkō (膝行, knee-movement), is considered more polite than standing up and walking regularly. Shikkō is today quite rare, but is found in some traditional formal restaurants and ryokan, and is practiced in the martial art of aikido, where practitioners learn to defend themselves while moving in shikkō.
To perform this knee-walking movement correctly the heels must be kept close together, and the body must move as a whole unit. It is because movement in shikkō forces one to engage the hips in a way that it is considered valuable for aikido training.
Alternative sitting positions
Sitting cross-legged, agura, is considered informal: it is appropriate for certain situations but not others. It is common in informal situations, such as eating at a low table in a casual restaurant, and allowed in formal situations especially for those for whom seiza is difficult, such as elderly or non-Japanese people.
Sitting cross-legged is generally considered uncouth for women, and female informal sitting has both legs off to one side, with one side of the hips on the floor, termed yokozuwari (横座り, literally "sideways sitting").
Another informal sitting posture for women is called wariza (割座, literally "separate or split sitting") which resembles seiza, but the lower legs are bent off to their respective sides.
To sit in seiza requires coming to a kneeling position momentarily, with the heels propped up; if one remains seated on the heels with the balls of the feet touching the floor and toes flexed forward, it is called kiza (跪座 / 跪坐). If one then lowers the tops of the feet to the floor, one then will be in the seiza position. In some schools of iaido, practitioners stand up to draw the sword and cut after momentarily assuming kiza, so as not to sprain the instep jumping up directly from seiza.