Zen is very simple to practice, yet very difficult to understand. Efforts and perseverance are required - like in life. By simply sitting, without looking for any goal or any personal benefit, if your posture, your breathing and your state of mind are in harmony, you will understand the true Zen, you will understand the buddha's nature."
« Zazen
is difficult, I know. But if practiced everyday, it is very effective
in broadening awareness and in developing intuition. Zazen not only
liberates a great energy, it is a posture of awakening. During its
practice you should not look to reach anything. Without focusing on
anything, it is only related to the concentration on the posture,
breathing and state of mind. »
Master Taisen Deshimaru
The posture
Sitting in the centre of the zafu (round cushion), cross legs in the lotus or the half-lotus position. If you encounter some difficulty, and if you just sit cross-legged, it is however necessary to push the floor firmly with your knees. The pelvis must be tilted forward at the level of the fifth lumbar vertebra. The backbone well erected, the chin pulled back and consequently the neck stretched out, the nose on a vertical line above the navel, push the floor with your knees and the sky with the top of your head.Put your left hand on the right one, palms turned towards the sky, thumbs touching each other and forming a straight line. Hands lie on your feet, their edges in contact with the abdomen. Shoulders are relaxed. The tip of the tongue touches the palate. Fix your sight roughly one meter on the floor without focusing on anything in particular.
Breathing
Zen breathing cannot be compared with any other. Very ancient it was named in sanskrit "Anapanasati", it can only be materialized through a correct posture. Its goal is above all to establish a slow strong and natural rythm, based on a soft, long and deep breathing out. Air is expelled slowly and silently through the nose, while the push created by the exhaling goes down greatly in the stomach. At the end of the exhalation, inhalation takes place naturally. The masters compare the zen breathing to the mooing of a cow or to the breathing out of a baby who cries as soon as he is born.The state of mind
During zazen, let the images, the thoughts, the mental shapes appearing from the unconscious, pass like clouds in the sky, without fighting them, without grasping them. Like the reflexions in a mirror, the expressions of the unconscious pass, pass again and then vanish. And one gets to the deep unconscious, without thinking, beyond thought (hishiryo), true purity.This state of mind emerges naturally from a deep concentration on the posture and breathing, allowing the control of mental activity resulting in better cerebral circulation. Indeed, during zazen, the cortex (the place of the conscious thinking) relaxes, whereas the blood flows towards the deep layers of the brain, which, being better supplied, wake-up from their light sleep. Their activity gives an impression of well-being, serenity, calm, triggering while still being awake, the cerebral waves of a deep sleep "alpha" and "thêta" (See on this subject the studies conducted at the University of Komazawa in Japan).
Source: Zen-Deshimaru.com