There is a physiological capacity that determines how well you sleep, how quickly you recover, how steadily you handle pressure, and how fluidly you move between effort and rest. It does not have a common name. Most people have never trained it directly.
It is the capacity of your autonomic nervous system to shift states on demand. To move into focus when focus is required. To downshift into recovery when the work is done. To mount an appropriate stress response when stress arrives, and to return to baseline when it passes. I call this capacity autonomic flexibility, and in more than a decade of clinical practice with athletes, executives, and operators, I have come to believe it is the most under-trained system in human performance.
This publication is about training it.
The framework I use to train it is called nervous system resiliency training, or NSRT. It is a structured, protocol-driven discipline that I have developed, grounded in two decades of research in psychophysiology, applied behavioral medicine, and HRV biofeedback. It is not a technique. It is not a tradition. It is not a hack. It is closest, in spirit and structure, to how exercise physiology thinks about cardiovascular training. There is a target adaptation, a primary stimulus, a measurement system, and a progression logic.
This first piece is the architectural map. Future pieces will go deep on each component. But before any of that work makes sense, the shape of the framework has to be clear.
The Adaptation: Autonomic Flexibility
Every training discipline is defined first by what it adapts. Strength training adapts the neuromuscular system to produce force. Cardiovascular training adapts the cardiopulmonary system to sustain output. Nervous system resiliency training adapts the autonomic nervous system to shift states.
Autonomic flexibility is not a mood. It is not a mindset. It is a measurable physiological capacity, expressed in the speed and precision with which your nervous system can move between sympathetic activation and parasympathetic recovery. The literature on heart rate variability, baroreflex sensitivity, and respiratory sinus arrhythmia has been quantifying this capacity for decades (Lehrer & Gevirtz, 2014; Shaffer & Ginsberg, 2017).
What does autonomic flexibility look like in a life? Falling asleep within minutes of getting into bed. Shifting from a difficult conversation into a focused work block without lingering activation. Recovering from a hard training session faster than you used to. Remaining steady during high-pressure moments that would previously have knocked you sideways. Returning to baseline after stress without rumination.
These are physiological outcomes, not psychological achievements. And like any physiological capacity, autonomic flexibility responds to structured training.
The Architecture
NSRT is built on three structural elements: a substrate and two training axes. The substrate is sleep. The two training axes are bottom-up and top-down. Everything else in the framework lives somewhere on this map.
Sleep is the substrate. It is not another health pillar or an equal partner. It is the physiological foundation on which any nervous system training is built. You cannot train autonomic flexibility in a chronically sleep-deprived nervous system, in the same way you cannot build strength in a chronically malnourished body. Sleep does not need to be perfect for training to work, but it needs to be sufficient. The training adapts what sleep makes available.
The bottom-up axis trains the autonomic nervous system through targeted physiological stimuli. The body is the input. The primary stimulus is resonance frequency breathing, a specific paced-breathing protocol, practiced at the individual’s unique resonance rate, that produces large coherent oscillations in heart rate and blood pressure. Over weeks and months, repeated exposure to this state strengthens the entire autonomic regulatory apparatus (Lehrer et al., 2003; Vaschillo et al., 2006). Other physiological stimuli sit on this axis as secondary tools, used to extend or support the primary work, but resonance frequency breathing is the foundation.
The top-down axis trains the autonomic nervous system through attention. The mind is the input. The primary practice on this axis is what I call mental attunement training, or MAT: the deliberate practice of attending to internal physiological and emotional state with the specific aim of informing autonomic regulation. MAT is distinct from mindfulness as it is commonly taught. Mindfulness, in most of its forms, cultivates a quality of awareness as an end in itself. MAT cultivates awareness as the lever for autonomic change. The lineage is real and worth naming, MAT draws from the contemplative traditions formalized in Mindfulness-Based Stress Reduction (MBSR) by Jon Kabat-Zinn, from Buddhist practice that long preceded it, and from the present-moment contact work of acceptance and commitment therapy. But the target is different. MAT is mindfulness sharpened to a physiological purpose.
These two axes work together, but they enter in sequence. Bottom-up first. The capacity to attend usefully to your internal state depends on having an internal state regulated enough to be worth attending to. Trying to do top-down work in a chronically dysregulated nervous system is like trying to read in a moving car. The bottom-up axis builds the stability. The top-down axis trains what to do with it.
What This Is Not
Four adjacent categories get confused with NSRT often enough that it is worth being specific about each one.
NSRT is not breathwork. Breathwork is a large umbrella that includes Wim Hof, holotropic breathing, box breathing, Pranayama traditions, and countless other practices. Most are taught as techniques for acute state change. Some are useful. None are built around resonance frequency as the primary training stimulus, and none track adaptation across weeks and months. NSRT uses breath the way strength training uses a barbell, as the instrument through which a measurable capacity is built over time.
NSRT is not meditation. Meditation, in most forms, is a practice of attention with mental cultivation as the primary target. NSRT inverts that, the autonomic nervous system is the primary target, even when the mental effects are real. (MAT, the top-down primary, is a closer cousin to certain meditation traditions, but its target and its measurement are different.)
NSRT is not vagus nerve hacking. Cold face plunges, humming, gargling, and ear-point stimulation have produced an entire cottage industry. Some have modest empirical support. Most do not. The deeper problem is that isolated vagal stimulation does not produce the sustained training adaptations that resonance frequency practice produces. Vagus nerve hacking treats the vagus as a switch to flip. NSRT treats the autonomic nervous system as a capacity to build.
NSRT is not stress management. Stress management is a psychological framing that focuses on cognitive reappraisal and behavioral coping. These are useful tools, and I use them in clinical practice. But they are downstream of the underlying physiology. NSRT targets the substrate. Stress management works on top of whatever substrate happens to be there.
Why This Matters Now
The last decade of wearable technology has taught an enormous number of people to pay attention to their nervous systems for the first time. That is a real contribution. HRV, once a niche metric used in academic cardiology and psychophysiology labs, is now displayed on millions of wrists and fingers every morning.
But something went wrong in the translation from the lab to the consumer.
The research that established HRV as a meaningful measurement was, almost without exception, research on interventions. Lehrer, Gevirtz, and the Vaschillos did not build the foundation of HRV biofeedback by showing that people who measure their HRV do better than people who do not. They built it by showing that people who train at their individual resonance frequency, for structured durations, over weeks and months, produce specific adaptations in baroreflex gain, vagal tone, anxiety, sleep, and emotional regulation (Lehrer & Gevirtz, 2014; Vaschillo et al., 2006).
The consumer wearable industry took the measurement and left the intervention behind.
The result is a generation of users who know their HRV score, watch it fluctuate, feel good when it goes up, feel bad when it goes down, and have no protocol for changing it beyond vague recommendations about sleep and stress. Tracking has replaced training. The industry has, largely, allowed this to happen because tracking is easier to sell.
Reading the gauge is not training the engine.
NSRT is the correction.
What This Substack Will Be
The Resilient Engine is the place where I will build out this framework in public, one piece at a time. Future writings will go deep on each component named here: resonance frequency breathing as the bottom-up primary, MAT as the top-down primary, sleep as the substrate, the secondaries on each axis, the assessment framework, the protocol structure, the dosing logic, the progression model, the individualization layer, the timeline of training effects.
Some pieces will be technical. Others will be argumentative. The conversation about how to train the nervous system has been dominated by the wearables industry on one side and the wellness industry on the other, and both have left the actual training discipline largely unbuilt. The work here is to build it.
If you have been tracking your nervous system for years without a protocol for changing it, this publication is for you. If you have tried breathwork and found it useful but vague, this publication is for you. If you are a clinician or coach looking for a structured way to think about autonomic training with the people you work with, this publication is for you.
The nervous system is the engine of human performance. It is also the system almost no one has been taught to train.
That changes here.
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References
Lehrer, P. M., & Gevirtz, R. (2014). Heart rate variability biofeedback: How and why does it work? Frontiers in Psychology, 5, 756.
Lehrer, P. M., Vaschillo, E., Vaschillo, B., Lu, S. E., Eckberg, D. L., Edelberg, R., Shih, W. J., Lin, Y., Kuusela, T. A., Tahvanainen, K. U. O., & Hamer, R. M. (2003). Heart rate variability biofeedback increases baroreflex gain and peak expiratory flow. Psychosomatic Medicine, 65(5), 796–805.
Shaffer, F., & Ginsberg, J. P. (2017). An overview of heart rate variability metrics and norms. Frontiers in Public Health, 5, 258.
Vaschillo, E. G., Vaschillo, B., & Lehrer, P. M. (2006). Characteristics of resonance in heart rate variability stimulated by biofeedback. Applied Psychophysiology and Biofeedback, 31(2), 129–142.
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Dr. Jay Wiles is a clinical health and performance psychologist, the Chief Health and Performance Officer at Ohm Health, BCIA-certified in peripheral and HRV biofeedback, and the originator of Nervous System Resiliency Training (NSRT). He works with athletes across the NHL, NFL, MLB, PGA, and Formula 1, alongside executives and operators in high-performance environments
THIS. There is a gaping hole in the space between HRV data & awareness of nervous system disregulation and a path to action & solving for the tools to manage this system. I am this person. Incredibly aware of my deficiency, an intellectual understanding of where it came from, data to support and no road to change. Thank you, Jay.