In zazen, we focus on the breath. The breath is life. The word "spirit" means breath. The words "ki" in Japanese and "chi" in Chinese mean, power or energy; both derive from breath. Breath is the vital force; it's the central activity of our bodies. Mind and breath influence each other. When your mind is agitated your breath is agitated. When you're nervous you breathe quickly and shallowly. When your mind is at rest the breath is deep, easy, and effortless.
It is important to center your attention in the hara. The hara is a place within the body, located two inches below the navel. It's the physical and spiritual center of the body. Put your attention and your mind there. As you develop your zazen, you'll become more aware of the hara as the center that connects the body and spirit.
In order to practice good zazen one has to have good posture, breathing, and ability to silence the mind. Good posture comes when you practice it every day of your life, but most people do not notice their posture. Most people have damage to their nervous system, the pain that alerts you from being in bad posture is the nervous system not functioning. Breathing is a physiological activity that will balance the two nervous systems in our body called Sympathetic and Parasympathetic Nervous systems. It will nurture your body and brain with oxygen and get rid of wasteful by-products of the body such as carbon dioxide. The ability to silence your mind is a very difficult task in this modern day. Everything is multi-tasking: at work, driving, parenting, and even your personal hobbies. In order to practice good zazen, the nervous system has to be nurtured and taken care of with no interference or any blockage of Chi. Chiropractic, Yoga, and Qi Gong helps remove blockages and restore optimum flow.