"Posture" refers to the physical form of our body while we are sitting. This posture is very ancient, and sitting postures similar to the one described here are common in many of the spiritual traditions that have their roots in India. There is evidence that some form of seated meditation was practiced there as early as 2000 BCE, long before the Buddha's time. According to Zen tradition, the Buddha was sitting in the posture of zazen when he attained enlightenment under the Bodhi tree, so the physical posture, in and of itself, is revered as the physical manifestation of enlightenment. In the Deshimaru tradition, careful attention to the precise details of the posture is emphasized. In Zen sitting, we practice as much with our body as with our mind.
Practically, sitting in this physical posture allows one to sit still for long periods of time with a combined sense of relaxation and alertness, although it may take some time for the body to stretch out, strengthen and adjust. The body is placed in a most efficient relationship to gravity, with the head being balanced on top of the spinal column. The shoulders can relax and hang down naturally. A loosening, stretching, and eventual relaxation of the abdomen is facilitated. The muscles of the back, necessary for keeping the body upright and the mind alert, are strengthened.
To sit in the correct posture, one should have a zafu, a traditional, round cushion stuffed with kapok. Begin by sitting solidly on the zafu, facing toward a wall, about four feet away from it. Establish a good, three-pointed base with your two knees pressing the floor and your buttocks on the zafu. You will have to experiment with the height of your zafu in order to get a sense of being properly balanced. Zafu height can be increased by turning the zafu on edge or by placing additional cushions or blankets under the zafu.
The preferred leg position is one of the cross-legged lotus positions. In the full lotus, the right foot rests on the top of the left thigh and the left foot rests on the top of the right thigh (either leg may be on top). In the half-lotus, the right foot rests on the left thigh while the left foot is underneath the right thigh (or vice-versa). In the quarter-lotus, the foot rests on the opposite calf. It is important to be able to have both knees firmly on the floor and to be high enough on the zafu so that you have a good arch in the lower back. An alternative to the cross-legged postures is the seiza, in which the feet are pulled behind you, alongside the zafu, shins resting on the floor. In the seiza, the knees should be about shoulder width apart and the toes should touch, or at least point toward each other, behind the zafu. For the seiza, the zafu should be turned on edge.
The pelvis is tilted forward so that the abdomen falls down naturally. There should be no obstruction of the abdomen, such as a tight belt. The spinal column is arched in the lower lumbar region, and then held erect, stretching out the backbone. The head should balance on the top of the spinal column, having a sense of pressing up, against the sky. The upper chest should be lifted so you have a sense of openness in the chest, but it should not be puffed out in an exaggerated way. Allow everything to hang from the spinal column. Relax the shoulders; relax the abdomen; relax the face.
The face is parallel to the wall, perpendicular to the floor. The nape of the neck is stretched. The mouth is closed, but the jaw and lips are not tight. Rest the tip of the tongue on the palette, just at the top of the front teeth. The eyes remain open, or half-closed, with the gaze directed downward at a 45-degree angle. The eyes should be still, but not focused on anything.
The lower forearms rest on the upper thighs with the palms of the hands facing up (sometimes it may be necessary to rest the hands on a small cushion or towel). There should be no effort or tension involved in holding up the hands and lower forearms. The fingers of the left hand rest on the fingers of the right hand. The thumbs cross over, their tips just touching. The thumbs should be parallel to the fingers, neither dropping down nor pushing up. It's like you are holding a large egg in your palms, surrounding it with your thumbs. The edges of the little fingers and the hands should make contact with the lower abdomen, just below the navel. The posture contains elements of both tension and relaxation. The backbone carries enough tension to keep the body erect, alert, and in proper alignment with gravity. Within that alertness, allow the body to relax, particularly the face, shoulders, and abdomen.
Once you settle into the correct posture, concentrate on that posture and on your breathing, returning your concentration to your posture and breath when your mind wanders. You should not move for the entire zazen period, except for slight movements as necessary to correct your posture. If you must move, you should do gassho before and after you move. At the dojo, one period of zazen usually lasts 30 minutes, 40 during a sesshin. You may experience some physical discomfort, even pain, depending on your age and flexibility.
Pain is something every Zen practitioner has to deal with, and working with one's physical experience of pain is an important part of practice. Learning to simply be with one's pain, to accept it for what it is, to let it be there, to relax the body and experience it are great teachings. This kind of pain is a physical manifestation of dukkha, here and now. As one Zen teacher said, "Where can you go to avoid pain?" That being said, zazen should not be excruciating, and sometimes pain is an indication that we are pushing ourselves too far and need to stop. Exactly where that point is can only be determined by each person. You certainly should not push yourself to the point of tissue damage.
There are also situations where someone may not physically be able to sit zazen in the manner described above due to injury, illness, age, or some congenital condition. When this is the case, the teacher can work with a student to modify the sitting posture so the person can still engage in practice.