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| Ladders Cross the Blue Sky in a Wheel of Fire by Joan Miro* |
Q: I am teaching a Pranayama workshop and linking it to Brain Physiology. I checked this article and I am confused. According to your article, inhalation stimulates the SNS (sympathetic nervous system) and exhalation triggers PNS (parasympathetic nervous system). Is this your personal experience or are you pretty sure about this correlation because I did not find this in any Yoga textbooks or articles.
Just think about Kapalabhati Pranayama: The inhalation is very passive and exhalation is very forceful. If your correlation is true, at the end of Kapalabhati pranayama, you need to feel more relaxed and calm (exhalation-PNS). But this is not what we typically experience. The nature of Kapalabhati pranayama is such that it makes an individual more active, there is more heat generated in mind and body and it awakens an individual from stupor. I guess this is due to activation of SNS. So this would be contradictory to what you mentioned. What is the correct explanation?
A: I love it when my readers take some aspect of the practice of yoga and begin to look a little deeper! I just reread my post How Your Breath Affects Your Nervous System on the effect of the length of the inhalation/exhalation (like a five-minute pranayama practice of one second inhalation and two second exhalation, for example) over time and the indirect influence it has on the brain and the “tone” of the autonomic nervous system (ANS). The length of your inhalation and/or exhalation influences your heart rate (cardiovascular system) by slowing or speeding it up, which then has a feedback effect on your brain’s perception of safety or danger, activity or rest, and may then shift the overall balance of your sympathetic/parasympathetic tone in one direction or the other. This assumes the person doing the pranayama does not have any other factors at play that might be more activating or quieting to their nervous system. For example, a new practitioner unfamiliar with breathing practices might be nervous and anxious about getting the practice right, and a breath ratio, such as 1:2, that might normally turn on the parasympathetic parts of the the ANS could be overridden by the background mindset of the person practicing it and actually stimulate the sympathetic nervous system instead.
In fact, the Autonomic Nervous System is by no way a simple system of the Fight or Flight response (sympathetic nervous system) being turned on and the Rest and Digest response (parasympathetic) being turned off, or vice versa. The ANS is much more subtle and nuanced than that. Why, just this past week, anatomy teacher and yogi Leslie Kaminoff’s colleague Amy Matthews wonderfully articulated this concept in this video clip.
As for the other kinds of breath practices our reader mentions, such as Kapalabhati pranayama, where the practitioner is quickly exhaling audibly, and quietly and more passively allowing the inhale to happen, and doing so at a pace that can be slower at first for newer practitioners or much faster in pace for more experienced practitioners, the typical effect is more stimulating for the ANS.
This means that for most people doing the practice, the sympathetic nervous system is likely going to be stimulated more. Even here, I could argue that the inhale/exhale length effects described above for slower kinds of pranayama techniques might still have an effect: the exhalation is short and quick, and the inhalation, which is not as audible as the exhalation, is probably a little longer in length than the exhalation. Done over several minutes, this could support the increase in stimulation of the sympathetic nervous system. In addition, the abdominal muscles are actively contracting to assist in the that quick exhalation, so you are asking your body to “work” more, which also will likely stimulate the sympathetic system a bit more.
This would be true also for Bastrika pranayama, where both the inhalation and exhalation are quick and audible.
In Bastrika, the length of the inhalation and exhalation are about the same, so you would not see the same influence of the length of the inhalation relative to exhalation that you do in Kapalabhati or the 1:2 ratio example I gave before. But because your abdominal muscles are so actively assisting the process, it is going to be more stimulating than quieting to your nervous system.
In all of this, keep in mind that it is not a simple formula of “this leads to that.” You will need to consider many factors when anticipating the effect that any particular breath practice might have, and, after practicing, also assess for yourself whether your predicted effect, either stimulating or quieting, really played out in the end!
—Baxter
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