The Paradoxes of the Autonomic Nervous System (ANS) & Where Unlimited Growth Lives | Brian MacKenzie

Issue #28

The Paradoxes of the Autonomic Nervous System (ANS) & Where Unlimited Growth Lives


The ANS is the largely unconscious regulator of our bodily systems. Yet, we also can control many of these systems through our manipulation. When we manipulate our breathing, we alter many, if not all, aspects of how the ANS functions. This is one paradox.

Another paradox is that as long as we’ve understood a bit of this system, we have communicated about the push/pull or antagonistic relationship between the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). So although there is a bit of one dominance over the other, the fact that the SNS is always on tells a different story. 

The third paradox is that although the PNS activates a calm side to us, it is anything but calm and may have more energy output than the SNS. We love to romanticize things far beyond our understanding of them for a good reason. It makes us feel good to think we fully understand something we’ve yet to fully understand, and I am no stranger to this. 

The ANS is engaged through nervous activity to help maintain homeostatic integrity and the functioning of our bodies as a whole. It responds to stress to maintain this integrity. 

Stress is the response of an organism to factors that actually or symbolically endanger its homeostatic integrity. It is any physical or psychological stimuli that disrupt homeostasis. The stress response happens through our sensory system; Interoception, proprioception, vestibular, visual, auditory, olfactory, tactile, and gustatory (taste). 

Our sensory systems are electrically based. Meaning you will need an ear for sound waves to be interpreted into nervous signaling to hear sounds. Otherwise, there is no sound, only waves.  

With the nervous system, stress involves all three branches of the ANS. I will focus on the SNS and PNS. The most basic version of this system works like this. 

In the presence of a stimulus, or psychological or physical stressor, we engage more of a response from the SNS, which activates the adrenal glands. When an acute stressor is no longer present, the PNS system facilitates the body’s recovery after the stressor. The PNS goes to work; it does not shut off. 

Your circadian rhythm has your adrenals releasing cortisol just before you wake. You go for a ride on your bike, and your body begins to go into the motions of preparing for more movement and using more oxygen. You get into a car crash, and hormones and neurotransmitters flood your bloodstream immediately following your NS response to the impact. The role of biochemistry following high SNS responses can not be understated, and I could write an entire article on one facet of it and still need to cover more. Biochemical reactions to the SNS can retard or suppress things like loud noises and pain in an emergency. This is simply a sample of the intelligence of our biology. 

Due to the nature and design of the SNS, we see that it is used to protect us. This protection aspect is much more important to understand than we have considered. Every part of us defaults to the modes of the ANS, as the entire organism of being human is built on a model of scarcity, except for our thinking brains, and yet we all behave and dip into scarcity thinking at times when we are – in truth – safe. 

When we engage in physical and psychological stress, symbolic or actual, we use acute survival strategies. These all come with circumstances; most of us have learned how to manipulate stress for our lifestyles. Consider briefly how many of our lives are tied around avoidance and protective behaviors that, for whatever reason, continue to drive the same tone of this SNS or PNS. 

As I stated, PNS is anything but an off-switch. It is just as involved in our survival as the protective side of the SNS, as it requires the SNS for the PNS to operate well. Don’t let the deceleration of our heart rates fool you, as there is a lot of nervous system activity going on when this side of the ANS is engaged. After all, all those protected organs and systems now return online to help preserve and regenerate those who went to work.


The SNS and stress. 

The sympathetic nervous system’s (SNS) primary process stimulates the body’s fight-or-flight response; in our world, that shows up as posturing or submissive behavior. Of course, it can also mean physically engaging in this fight response through work or activity. Still, it is typically accompanied by posturing or submissive behavior, as we have patterns of behavior that follow biochemical activity through our experiences. Since energy sits at the foundation of life, the SNS’s primary job is also to mobilize glucose. I’ll come back to this. 

The SNS is constantly active at a basic level to maintain homeostasis. It is traditionally described as antagonistic to the PNS. It isn’t if it is always on. 

It is essential to note the posturing and submissive behavior with fight or flight. As far as I understand, this was something Lt. Col. Dave Grossman came up with. He used it to understand the psychological costs of being at war and coming home. That said, looking at the many behavioral patterns of posturing and submissiveness, this is a unique opportunity to understand more about how you can tend to lean into more dominance of this part of your ANS. 


Quick examples: WE ALL DIVERT INTO VERSIONS OF THESE. However, I am not here to analyze you; that is your job. My suggestion is PAY ATTENTION. 

Posturing: behaviors related to impressing or intimidation (we all have them)

Submissive: behaviors related to shying away or not saying what we want (we all do it at times)


When we engage more in this system, we will begin to engage in nervous activity toward more energy mobilization (glucose) and the necessary metabolic shifts that all come with a cascading of energy from ATP, lactate, hormones, neurotransmitters, immune response, proteins, genetics, and plasticity.  

Our interoceptive experience begins with whether we like what we feel or not. Then, what do we do if it’s a threat or if it’s just exciting? This can follow several paths (refer back to posturing submissive behaviors) that ultimately can land with how we like to do things or don’t. We often keep repeating a process, getting the hormones and neurotransmitters of our liking that continue to express genes and layer in our conditioning (plasticity).

Culturally we are running hot, and by the looks of the global consensus, most of what is killing us is living in this SNS dominance. 

Globally, Cardiovascular Disease is the number one killer. We can lump blood pressure issues into that. Then, bring in metabolic disorders; most cancers, obesity, and diabetes are up there too. While nutrition plays a significant role in all of this, consider that the constant ON and demand for ATP with the mobilization of glucose for symbolic issues are pushing our physiology to respond by activating a muscular system that isn’t engaging in the actual fight/flight responses; meaning instead it becomes posturing and submission– acting out. Note: When I use the term ON, I am also writing about emotional intelligence and reactivity or suppression of these emotions and, ultimately, feelings. 

From an acute basic perspective, the SNS does the following:

  • Increased HR 
  • Increased Blood Pressure
  • Increased Respiration
  • Increased Attention
  • Decreased Fine Motor Skills 
  • Decreased CO2 Levels
  • Decreased Digestion
  • Dilated Pupils

Most of my 30s were spent running in a chronic state of survival. I was convinced this was perfectly normal, until it was not. With the above information and knowledge about disease, what do you believe the outcome of long-term chronic SNS behavior has on us? 



The PNS and its role in stress are as essential as the SNS.  

The PNS stimulates resting, feeding, digesting, and reproductive activities when the body can relax. Although these activities typically occur after eating or exercising, they include sexual arousal, salivation, urination, digestion, and defecation. The PNS is a complementary action to the SNS. 

Pay attention to the activities I mentioned, as we can start to understand where we might indicate where our ANS is getting “sticky.” More on this in a minute. 

While many overreaching issues can happen with the PNS, it is essential to note that, in my experience, this is due to needing to understand our SNS engagement. Overreaching is the body’s attempt to keep us down a bit longer. From an HRV perspective, this is leaning more heavily into the PNS. From a feeling standpoint, we are much more lethargic. This does not, however, mean we are shut off and less activity is going on in the body or nervous activity. This means more energy and action are being engaged towards getting the systems, tissue, and organs associated with this side of the ANS the appropriate time to respond and restore themselves. It requires nervous activity. It requires energy.

An overactive PNS is associated with more depressive-like behaviors. However, that does not mean someone is depressed or diagnosed with depression; this outlines that in more depressive behavior, we see a more active PNS. While these behaviors may look like inactivity, the internalization occurring with these behaviors is anything but inactive. Much like the SNS, there can be a propensity to lean into the chemical processes or biochemistry associated with these states. There is a particular flavor we all lean into, and although genetics plays a role in this, it does not always mean something is wrong. Often most of us may want to listen a little bit more intently.

Much of what we see is related to this, and we all fall into this from time to time; lethargy, stress sensitivity, similar to the SNS – avoidance or submissive behavior, or a general lack of motivation. When we fall into these submissive behaviors, we can quickly transcend into staying in them and ultimately struggling to get out. Eventually, we should seek professional help when this is no longer acute or short-term. 

Returning to the activities involved in the PNS; resting, feeding, digesting, and reproduction. One way to understand where you may have an opportunity to learn how or where you lean with SNS dominance is when one or some of these activities struggle to operate well. 

Examples: however, not relegated to these

Struggle to relax, rest, nap, or sleep.

Struggle with appetite and digestive issues (this can and does affect the Enteric Nervous System, another side of the ANS). *of note, make sure you’ve addressed nutrition too. 

Struggle with libido issues or not having a healthy sexual appetite. 

Please pay attention to addictive behaviors (we all have them) towards any one or all of these, as this has become a coping strategy, and more than likely, at the root of this, is our inability to regulate the relationship of our ANS. There can be many versions or variables to this, so take your time and just learn to pay attention. 

Many of us struggle to want to look at the reality of our struggle to regulate. We use alcohol and drugs in the evening as a normal response to unwinding because many people we associate with do the same thing. We eat and crave sugar at night after we eat to fulfill the same void and a NS that has depleted the body of glycogen as we struggle to eat regular meals during the day. There are many ways to understand our behavior, and I’ve looked at several of them. The truth is cutting out the sugar, or the booze might change some things. However, suppose we pay close enough attention to learning to observe our behaviors associated with regulating these states of our ANS. In that case, you will begin to get a blueprint of where some of the lowest-hanging fruit of your growth exists. 

The only growth that comes from removing something without understanding its root is an opportunity for the next vice to take its place. And so the cycle repeats.

The basis of SH//FT Health is built off this entire piece. The framework for everything we are doing at SH//FT – albeit piecemeal at times – is also embedded in this. Should you be interested, we kickoff a new Health program that gets right to the point with all of this on July 19, 2023, and we’d love to see you. Click HERE 


  • Natalia Bobba-Alves, Robert-Paul Juster, Martin Picard, The energetic cost of allostasis and allostatic load, Psychoneuroendocrinology, Volume 146, 2022, 105951, ISSN 0306-4530, 
  • Cristina Rabasa, Suzanne L Dickson, Impact of stress on metabolism and energy balance, Current Opinion in Behavioral Sciences, Volume 9, 2016, Pages 71-77, ISSN 2352-1546,
  • On Killing: The Psychological Cost of Learning to Kill in War and Society is a book by Dave Grossman 
  • Halson SL, Jeukendrup AE. Does overtraining exist? An analysis of overreaching and overtraining research. Sports Med. 2004;34(14):967-81. doi: 10.2165/00007256-200434140-00003. PMID: 15571428