Answers to Questions on the Contemplative Practice of the Four Foundations of Mindfulness (Satipaṭṭhāna-vipaśyanā-caryā) 8

Question: Why do I feel my breath becoming shorter and slower as soon as I settle down? When my mind is not yet calm at first, my breath feels relatively long. After settling down, I let the body breathe on its own and observe that the breath does not reach the dantian; yet if I control the breath and deliberately make the inhalation longer, I can no longer stay calm. 

Answer: When the mind settles down, attention is focused on the breath, and at this point one may involuntarily control the breath somewhat, or pay rather close attention to it, so the breath feels shorter and slower. Only after freely entering meditative concentration (samādhi) and the mind becoming calm will the breath become long. When the breath is naturally short, it indicates that the circulation of the body's qi channels is not yet smooth, and that one's skill in sitting meditation and cultivating meditative concentration is insufficient—more practice in sitting meditation and cultivating concentration is needed. When there is no meditative power, or it is very weak, controlling the breath may cause the mind to become scattered, and the mind can no longer be calm. Controlled breathing is not natural breathing, not the normal state of breathing; only uncontrolled breathing is the normal state. However, in order to adjust the body and let the qi channels flow smoothly, one may, of one's own accord, engage in focused deep-breathing training, allowing the breath to open through the five zang and six fu organs, and this can also incidentally deepen dhyāna concentration.