Understanding your autonomic nervous system
You are walking down a forest path with your thoughts turned inward. Barely aware of your surroundings you focus on breathing into your entire body and clearing your mind of the stresses of the day. With each breath, you feel yourself sinking deeper into a feeling of calm relaxation. Suddenly, shaking your peace, you hear a rustle in the bushes ahead of you. A small grizzly cub awkwardly pushes its way through the brush and stumbles onto the path. You freeze, and your thoughts start to race...if the baby is right there then the mother has to be nearby. Almost as if your mind is creating your reality, on cue, you hear the muffled grunting of a mother grizzly just ahead of. She bursts on the path ahead of you with a thud and immediately picks up your scent. Clearly feeling the protective instincts honed by millions of years of evolution, the mother rears up onto her hind legs, a towering pillar of fur and muscle. Hundreds of thoughts race through your mind, you are barely able to determine one thought from the next. An instant later the choices before you are clear: hold your ground or make a break for it through the ravine to your left. Fight-or-flight signals course through your nerves and permeate your entire body - your blood vessels dilate, muscles tense for action, and just before you make the first move to tear down into the ravine and flee certain peril, your feel the cool comfort of your bed covers and quickly realize that you've been dreaming.
This story is meant to illustrate the full range of arousal, from calm relaxation to heart-pounding fear controlled by your autonomic nervous system (ANS). This is the system that is responsible for keeping the majority of our basic body systems functioning, and works at a subconscious level at all times during the day to keep us in a state of balance. There are two major divisions of the autonomic nervous system: the parasympathetic division (usually referred to as the rest & digest or the feed and breed system) and the sympathetic division (fight, flight, and freeze). The two divisions of the ANS work together in concert, a constant tug of war, to prepare our body for stress and action or to calm us and help us adapt to those stresses. From the simple observation of elite athletes we can see that balance between the two influences plays a role in determining their ability to adapt to training. For those seeking to optimize health and performance, understanding how to influence this tango can be a major (and probably biggest) first step.
The remainder of this blog will be a primer on the autonomic nervous system, the types of stressors which impact your ANS, and an exploration of some tools for altering your ANS activation.
The ANS is an “old” part of our brain from an evolutionary perspective. As a result it plays a role in controlling the basic necessities for life including the regulation of heart function, breathing, and reproduction. As we discussed in the introduction, there are two basic divisions of the autonomic nervous system: the parasympathetic (PSNS) and sympathetic (SNS) divisions. They play opposing roles pulling us into and out of heightened states of arousal and relaxation based on the demands from our environment.
Activation of the parasympathetic division stimulates a “relaxation response” by regulating heart rate and breathing, promoting digestion and absorption of nutrients, facilitating the initiation of reproduction, decreasing resting muscle tension, and reducing inflammation. When the PSNS is dominant we tend to turn our focus inward and become more aware of the functions of our body and the way we move (making it vitally important that we activate our PSNS prior to doing “movement” work). From a practical standpoint the PSNS facilitates recovery from and adaptation to stresses, like a hard training session. The more frequently we facilitate relaxation through the use of breathing drills or low intensity movement the better our brains become at snapping back into relaxed PSNS states after a period of high stress.
Activation of the sympathetic division (SNS) on the other hands stimulates our “stress response”. The functions of the SNS are the opposite of the parasympathetic division. Activation of our SNS is our brain's way of reacting to stresses in our environment. When we perceive a stress our SNS becomes more active preparing us to fight, flee, or freeze. We become more aware of the environment around us, adopt more aggressive postures with increased muscle tension, and prepare our physiological systems for action. When the SNS is active, we are ramped up and ready to react to our environment.
The interplay between these two systems is extremely complex, however from a basic standpoint “stress” triggers SNS activation and “rest” triggers PSNS activation. There are a number of things that cloud this simple model, aside from the fact that the distinction between stress and rest is like distinguishing between shades of grey. The health of our body and nervous system has a big impact on our ability to achieve effective relaxation responses through PSNS activation. Things like poor posture and breathing mechanics (the two are tightly linked together) or inflammation of the organs controlled by the autonomic nervous system (gut, lungs, heart) can inhibit our ability to move easily back into a resting, PSNS dominated state after experiencing stress.
I look at potential stresses in three different categories: exertional, environmental, and cognitive. I am also aware that these are not traditional definitions of stress, however I have found them far more applicable as a coach and athlete for understanding how stress impacts my athletes.
Exertional stresses are physiological manifestations of physical output. In other words the actual impact of exercise and movement on the internal environment of our body. Increasing intensity of physical exertion will result in increased stress on the internal “system”. For example, walking for one-mile imposes relatively little stress on our bodies compared with running a one-mile time trial or performing a high-intensity interval weight training session. The mismanagement of training load (intensity x volume x frequency) can quickly create chronic states sympathetic overload and result impaired adaptation. Many of us who are in the coaching space have seen this happen, athletes progress quickly with the application of big training loads, then stagnate, then they break. Proper balance between exertional stress and recovery work is key.
Environmental stresses are physical factors in the external environment of our body that lead to activation of our stress responses. The best examples of this come in the form of food allergies as these tend to be the most extreme and can be clearly observed. However for the vast majority of us environmental stresses are less “severe” and go unnoticed. Things like courses of antibiotics killing off our gut flora, air pollution, under and overeating, poor food quality, and joint or organ inflammation can all interact together keeping us in a low-grade, chronically stressed state. Our autonomic nervous system has nerves (Vagus nerve is the primary) which respond to distress in our internal environment. The state of our internal health can influence the balance between SNS and PSNS dominance, thus maintaining our a general state of health is a key to maintaining optimal balance between stress and recovery.
Cognitive stresses are things we perceive as threatening, leading to changes in our ANS state. In other words stresses imposed by our thoughts and emotions or non-physical “potential” threats in our environment (the mamma grizzly in the introduction). Worry is one of the most obvious examples of cognitive stress as it can often lead to perceptible increases in our feelings of stress and anxiety. Major life events like a death in the family, divorce, or losing your job can trigger cognitive stresses and the impact is very obvious (except sometimes to the person going through the event who often lacks the self-awareness to recognize the stress). However I think there are other examples of cognitive stress that we tend to be much less aware of including watching intense or suspenseful shows or spending time on social media. These stimulate the SNS at a lower level, by forcing us to be more sensitive to our external-environment during times we should be relaxing and tuning into our internal-environment. Of all of the types of stress inputs, I think these are probably the most damaging to our health and performance. The activation of the sympathetic system prepares the body for action - but in the case of cognitive stresses there is typically no subsequent action and therefore no physical stress for the body to adapt to.
Like everything in life, the lines between these categories cannot be clearly defined, but they are useful for developing an understanding of what factors may be influencing your ANS and subsequently health. Problems arise when we spend too much time in stressed, SNS dominate states. Those temporary responses of the SNS to stress like hypersensitivity to our environment, chronic muscle tension, and the stiffening of posture become long-term adaptations. Constant environmental hypersensitivity feeds right back into the autonomic nervous system making it difficult to “turn off” and achieve relaxed PSNS dominate states. Increased muscle tension manifests as deteriorating posture which negatively impacts our ability to breathe fully, again feeding back into the autonomic nervous system locking us into chronic states of stress. The eventual result is an overall deterioration of health and resilience to all forms of stress (including the ability to handle training loads that you once considered mild).
Most people involved in the training space, whether in team sport, CrossFit™, or bodybuilding are good at creating stress and training hard. However, most of those same people struggle to adapt properly to training-loads that they should be able to handle. I think this is where the phrase ‘there is no such thing as overtraining, just under recovering’ comes from. If you’ve ever had the chance to spend time with elite athletes away from their training environment, you likely have observed that they seem to be more laid back and less affected by things that would cause stress in others. It can appear as if they are impervious to the stresses that affect the rest of us. However, based on my experience they are better at shielding themselves from stressful people and events and better at reframing events into a context that doesn’t threaten them. Elite athletes are people who put a hefty price on the importance of quality sleep, truly relaxing and shutting their brains off, working on their movement quality, and managing their stress inputs. While they may not know that getting into this relaxed state means they are driving parasympathetic activation and thus reducing systemic inflammation or reducing resting muscle tension, they do know that when they do it frequently they feel better and recover faster. This is reflected by their longevity in the sport, their ability to stay injury free longer, and overall healthy vitality.
The consequences of chronic stress and sympathetic activation are clear. Further the correlation between optimal performance and effective management of the stress / relaxation balance is even more clear. There is no denying that people subjected to an overload of stress-inputs will see deteriorating health and subsequently performance if this is not balanced with good recovery habits (read: parasympathetic drivers). So this begs the question: what strategies exist for driving parasympathetic activation? A good starting point is to look at the recommendations coming from the health, relaxation, and performance space. Cardiologists suggest stress relief programs and moderate intensity cyclical exercise (note to most athletes, “moderate” intensity exercise would feel quite easy relative to a typical training load and would constitute EN1 or EN2 training in the TTT energy-system training categories). Functional medicine doctors address dysfunction in various organ systems giving the gut-brain axis a great deal of attention in their prescriptions. Yogi's and other experts in the relaxation space suggest specific breathing routines and low-intensity movement to help people reduce stress and calm their minds. The best coaches in the sport-performance space advocate creating balance between low and high-intensity training with a focus on improving movement quality and implementing recovery techniques (which typically include some form of breathing and relaxation work). If you stop for a second and think critically about these recommendations, you begin to see the bigger picture: experts in nearly every field related to health and performance are recommending that you take steps to reduce sympathetic stress inputs and increase activation of parasympathetic, relaxation. In other words to recover well and optimize our health we must implement strategies to balance our autonomic nervous system.
We know that the ANS works below the level of conscious control, but we do have ways to influence the parasympathetic branch. The easiest and most obvious place to start is to remove stress-inputs which would by definition reduce SNS activation and shift the balance to the PSNS. Good strategies for reducing stress-inputs include: resting or implementing low-intensity “recovery” work to your training (reducing exertional stress), disconnecting from social media, managing your time better to reduce worry, and eliminating unhealthy habits and environmental factors from your life. At first glance these seem like minor things that might have little to no impact on recovery, however implemented over time these “lifestyle” factors create the only environment that is conducive for optimal health and performance.
Beyond controlling our exercise and environment we do have some tools that can have a direct impact on driving parasympathetic activation. As it turns out, breathing is our most direct access point to influence our ANS. Our heart rate (and thus ANS control) is so tightly tied to breathing that we can actually observe an increase in instantaneous heart rate when we inhale and a decrease when we exhale. At rest we can use extended exhalation and diaphragmatic focused breathing to stimulate a relaxation response and increase parasympathetic drive. Breathing cadence drills like: inhale for four seconds / exhale for eight seconds, exert powerful control over our ANS. Routines like this, performed consistently, can lead to a reversal of some of the impacts of chronic stress-induced SNS activation. Research consistently shows that activation of our PSNS through the use of breathing drills reduces whole-body inflammatory markers which we can use as a proxy illustrating just how global the impact of relaxation work actually is.
Another effective tool we have for increasing PSNS activation is the use of cold water exposure. This can be in the form of a cold shower or dunking your head in a bucket of cold water. The cold water acts as a temporary "stress input" that paradoxically triggers the activation of the parasympathetic system to quickly calm us after the shock of contact with frigid water. Again, just like the implementation of relaxation breathing drills, cold water exposure can condition the ANS to handle greater "stress loads" like increased training volume, or bigger disturbances in our homeostasis (like viral infections). My personal recommendation for using cold-exposure is to start with cold-showers as this allows you to progress into the cold both during the shower and to colder temperatures over-time. To start, get into a warm shower and progressively lower the temperature every 30 seconds until you’re at the point where the temperature is starting to affect your breathing rate. Stay there for 2-3 minutes and then end the shower. Over the course of a couple of days you will be able to relax in colder temperatures and can continue to progress the temperature down. Ideally we want to spend two or more minutes in the cold to have a significant impact on our ANS.
As an organization searching for ways to help people optimize their health and performance we have placed great importance on the impact that the ANS can have on our overall wellbeing. It has become clear to us that most people need to be taught to relax and find balance in their training. As a result, we continually push our athletes to develop greater self-awareness of their stress-inputs and lifestyle factors to help guide their training. My personal hope is that the athletes I work with and those who consistently read our blog will develop habits which lead them to better performance in their current training journey - but also recognize the benefit that those same habits hold for improving their health and happiness outside of the training space.