Here are the notes I prepared for the dhamma dialogue .mp3 file which is posted next: “Calming The Breath Body”.  The next posting after that is an .mp3 recording “Guided Calming The Breath Body Meditation”.  I hope they are useful for your practice of anapanasati (mindfulness of breathing).

I’ve already explored in a previous posted essay “acquiring the breath”, the ability to bring attention to the breath (vitakka) and sustain active interest (vicara) in the changing sensations during the breath cycle. This essay will explore how to make use of the suggestions in the Anapanasati Sutta to promote deeper physical relaxation and emotional tranquility while still maintaining and even increasing alert inner awareness.

Here is a section from the sutta that is relevant to the essay:
He trains himself, ‘I will breathe in sensitive to the entire body.’ He trains himself, ‘I will breathe out sensitive to the entire body.’ He trains himself, ‘I will breathe in calming bodily fabrication.’ He trains himself, ‘I will breathe out calming bodily fabrication.’ (Translated by Thanissaro, downloaded from Access To Insight)
Just to make it interesting, here is an alternate translation by Gil Fronsdal, a well-respected teacher and translator, of the same part of the sutta:
He trains himself ‘breathing in, I experience the whole body. ’‘Breathing out, I experience the whole body.’
He trains himself, ‘breathing in, I calm the bodily formation. ‘Breathing out, I calm the bodily formation.’ (downloaded from the Insight Meditation Center)

There is ongoing debate about what the “whole body” is. Many translators and teachers say this means all of the in-breath and all of the out-breath with no deviation or interruption. Others, equally qualified, suggest it means that the breath awareness remains “core” for attentional focus, and the rest of the body is experienced as well, again, with no deviation or interruption. The essence of both approaches is that the more consistently sensations in the body are attended to, particularly the breath, the less intrusive the internal commentary is.
It’s tempting to have the view that this means no thoughts are in awareness. I don’t believe this is as important as some of the commentaries suggest. In my practice experience, breath awareness is the primary point of focus, the “home base” that is returned to when attention is drawn to an alternative focus. It’s the nature of the mind to “check out” novel sensational input, however briefly. I think this training simply means that breath awareness is predominant. The important point to consider is the degree to which the distracted awareness becomes preoccupied with the alternative focus, that is, creating a narrative, and a “selfing story” emerges to take over. With breath awareness there is no selfing story, there is just sensational awareness without commentary. This can also be true of unelaborated physical sensations. This foundational awareness serves to interrupt the “buildup” of craving and clinging associated with the emergence of the internal narrative.
When the selfing story elaborates, the degree of relaxation and calmness that was developing with ongoing, predominant breath/body awareness diminishes, as the nervous system and hormonal system associated with the narrative activates the whole body. This phenomenon can be noted with sufficiently developed mindful awareness, involving the developed pattern of vitakka and vicara that is first established at the beginning of the practice. Mindful attention (vitakka) goes to the distraction, and ongoing awareness (vicara) checks out the novel stimulus. Then the practice is to disengage from the stimulus before it develops into a selfing story and then re-engage breath awareness.
The more the distractions are noted and disregarded, the calmer and less turbulent the flow of energy in the mind is, and the more relaxed the body is. An analogy I frequently use is what happens when a stick is thrown on a fire. The stick doesn’t immediately disintegrate; it takes a while for it to burn out and it generates a lot of heat. When the “stick” of craving and clinging is activated, typically involving an internal narrative, excitatory hormones are injected into the blood stream. This creates “heat”, that is, the muscles tighten, blood pressure elevates, etc. It takes some time for the actions of the hormones to metabolize out of the system. When the mind becomes trapped in the selfing story, whether it’s pleasant or unpleasant, it’s like more sticks being thrown on to the fire! When attention is brought to the breath/body sensations, there is no hormonal excitement involved. This interval tends to create an internal “space” of non-reactivity, allowing the system to settle down. The longer the neutrality of breath/body awareness is sustained, the more opportunity there is for the hormonal “fire” to subside; this promotes physical relaxation. The degree to which one actively investigates the particular sensations of the breath/body, the more alert the mind is, while also becoming more tranquil! This is what manifests as “Breathing in I experience the whole body…Breathing out, I calm the bodily formation”. Experiencing “the whole body” includes breath awareness, body awareness and awareness of what’s “pulling” attention into a selfing story. The result is “I calm the bodily formation”.
I practice this by focusing on the sensations of the in- and out-breath, “zooming in” a focused attention on the sensations around the rim of the nostrils. I experience this as the breath sensations seem to “expand” in subjective awareness, “taking up more space” in consciousness. As this becomes established, I also practice intentionally allowing relaxation of the body/mind processes to develop with the out-breath. This tends to naturally slow and lengthen the duration of the out-breath. With this letting go associated with the out-breath, I notice and release whatever physical tension I might notice, even when the tensions are quite subtle. When you think about how the muscle we call the diaphragm, (which controls the cycle of breathing) operates, it tenses up with the inhalation and relaxes with the exhalation.
The next level of practice explored will be the stanzas associated with how further development of breath awareness leads to an emerging heightened interest in the investigation of mental phenomena.