The most important thing, whether we are sitting in a cross legged or a kneeling position, is to have our pelvis in the correct position. Habitually, people tuck their pelvis forward. The effect of that is to collapse the chest and bow out the back, and push the head forward. We then try to correct this with our voluntary muscles, but we can’t maintain it, and so we alternate between muscular effort and collapse.
To remedy this, we need to sit on our sit bones. The best way to achieve this is, as we sit down, to stick out our buttocks, bringing our weight forward onto the knees and creating a curve in the lumbar spine. If we are balanced on our sit bones, we will be able to sit upright without muscular effort. Our weight will drop down through the sit bones into the Earth. Releasing the weight into the ground creates a corresponding push from the Earth, up the spine, allowing the spine to lengthen and relax. Our large postural muscles at the front can become engaged, holding us up without effort, and making the posture more energetic.
If the pelvis is in the correct position, it is far easier to correctly align the head, which is normally pushed a bit forward, like a tortoise. We can simply drop the head back and slowly bring it to vertical. The point of balance is normally a bit further back than we are used to. If the head is balanced, it should not feel heavy. Sometimes, when the head is in the right position, a breathing reflex is set off in the lower abdomen.
The posture is dynamic. The head and the upper body should not feel heavy. If they do, it is indicative of you not being in the right position.
You will sometimes hear that you should tuck your chin in and extend the back of the neck. This is a terrible instruction, as it simply creates tension in the neck. If your head is in a balanced position, your chin will be slightly tucked in, but this is a consequence of your good alignment. It should not be forced.
Rather than try to stretch the back of the neck, you should allow the neck to naturally lengthen. A way to do this is simply to be aware of tension you are holding in your throat, and allow your lower jaw, at the hinges, to go up, without making any muscular effort. You can do the same thing with the top of your hard palate, allowing it to rise and being aware of the connection between it and the crown of your head. The push which enables both of these to rise comes from the pelvis, not from muscular effort. If we use our voluntary muscles to push us into what we imagine to be a good posture, we are practicing Ego, not Zazen.
Don’t try to control the breath. If you are in a balanced position, you will naturally breathe from the abdomen, but don’t artificially restrict your breathing to that area. Remember that the breath flows first into the belly, then into the back, then into the chest.
When we are doing Kinhin, we take a small step forward with one foot. Placing the heel of the foot down, we spread the toes and, breathing out, we roll the weight forward from the heel to the top of the toes. All the weight is then on the front foot. Breathing in, we then push down near the root of the big toe, stimulating the Bubbling Stream acupressure point and allow the push to travel up our front leg, up the front of our spine, up through the top of the hard palate, and out through the crown of the head. Towards the end of the in breath, with all the weight on the front foot, we bring the back foot forward, heel down, and do the same with that foot, in this way walking slowly round the room. Our pace is regulated by the length of our breath. If we are moving slower than the person in front of us, we can take bigger steps. If we are moving faster, we can take smaller steps.