By: Bhikkhu Analayo
The sitting posture needs to be such that the spine is kept straight. Here some degree of continuity of attention to the posture is required to avoid and slumping of the body….Keeping the body erect could be achieved by slowly passing our attention through the spine from bottom to top, relaxing each vertebra. Such relaxing enables a natural alignment of the spine, by just letting gravity pull downwards. The overall sense is as if the body were suspended from above, at the top of the head, and the rest of it relaxes downwards. The resulting erectness of the body is not something to be held in a fixed manner. Instead, the body remains flexible, comparable to a slender tree in the wind. Such flexibility allows for minor adjustments to occur whenever we notice that the body is not fully in balance. Needless to say, this does not mean that we keep shifting around all the time, but just that we avoid holding the posture rigidly and with tension, be it when sitting on the ground, a cushion, a bench, or a chair.
In order to keep the body erect, we of course need to be aware of it. Thus…[we] establish awareness of the body as a whole in the sitting posture and to some degree also monitor it throughout the meditation session, at least until such a deep level of concentration is reached that the posture of the body naturally remains firm.
From Mindfulness of Breathing. Bhikkhu Analayo is perhaps the foremost contemporary scholar-monk in the Theravadin tradition. Among the many books that he has published, his works on the four foundations of mindfulness—Satipatthana: The Direct Path to Realization and Satipatthana Meditation: A Practice Guide—are exceptional.