THE SCIENCE
How your nervous system
actually works under pressure
The principles behind this work. Accessible, research-grounded, and focused on what changes when regulation improves.
THE NERVOUS SYSTEM
Two systems.
One operating your body without your permission.
Your autonomic nervous system runs continuously beneath conscious awareness. It manages heart rate, respiration, digestion, immune function, and hormonal output. It has two primary branches.
The sympathetic branch mobilises you. It increases heart rate, sharpens attention, releases cortisol and adrenaline. This is the system that activates under pressure — meetings, deadlines, conflict, threat. It's designed to be temporary.
The parasympathetic branch restores you. It slows heart rate, deepens breathing, supports digestion and immune function. This is the system that allows recovery, sleep, and clear thinking. It's supposed to be your default.
Regulation is the balance between these two branches — the capacity to activate when needed and recover when the demand passes. When this balance is disrupted, the consequences show up everywhere: decision fatigue, disrupted sleep, chronic tension, emotional reactivity, and a narrowing of cognitive capacity under pressure.
Most people operating at a high level have been running sympathetic-dominant for so long that the activated state feels normal. The body adapts to the load. The adaptation has a cost.
The autonomic nervous system doesn't distinguish between a genuine threat and a perceived one. The body responds identically.
PORGES, S. — THE POLYVAGAL THEORY, 2011
BREATH AS LEVER
Your breathing pattern is both a readout and a control input
Respiration is the only autonomic function you can also control voluntarily. This makes it a unique interface between the conscious mind and the nervous system. Your breathing rate, depth, and pathway (nasal vs oral) directly influence which branch of the autonomic system is dominant.
Breathing rate. At rest, a well-regulated nervous system breathes 4-6 breaths per minute. Most adults breathe 12-20. Faster breathing drives sympathetic activation. Slower breathing — particularly with extended exhale — engages the vagus nerve and activates parasympathetic recovery.
CO2 tolerance. Carbon dioxide is commonly misunderstood as a waste gas. It is a vasodilator that improves oxygen delivery to tissues, including the brain. Habitual overbreathing reduces CO2 levels, which paradoxically reduces oxygen utilisation — a pattern called the Bohr effect. Training CO2 tolerance through breath-hold work and reduced-volume breathing directly improves cognitive function and stress resilience.
Nasal breathing. Nasal respiration filters, humidifies, and warms air. It also produces nitric oxide, which improves oxygen absorption by 10-15%. Chronic mouth breathing elevates sympathetic tone, disrupts sleep architecture, and reduces CO2 tolerance. Transitioning to consistent nasal breathing — especially during sleep and low-intensity exercise — is one of the highest-impact changes available.
A single shift from oral to nasal breathing during sleep can reduce sympathetic nervous system activity by up to 20%.
NESTOR, J. — BREATH: THE NEW SCIENCE OF A LOST ART, 2020
4 - 6
OPTIMAL BREATHS PER MINUTE
10 – 15%
OXYGEN ABSORPTION GAIN VIA NASAL BREATHING
20s+
BOLT SCORE INDICATING HEALTHY CO2 TOLERANCE
HRV AS BIOMARKER
The single most useful metric for tracking nervous system capacity
Heart rate variability (HRV) measures the variation in time between successive heartbeats. A higher HRV generally indicates a nervous system with greater adaptive capacity — the ability to shift between activation and recovery as conditions change.
HRV is influenced by sleep quality, physical fitness, stress load, emotional regulation, and respiratory patterns. It declines with chronic stress, poor sleep, overtraining, and sustained sympathetic activation. It improves with consistent regulation practices, adequate recovery, and respiratory training.
What HRV tells you. A single reading is a snapshot. Tracked over time, HRV reveals trends in your regulatory capacity — whether your baseline is improving, degrading, or plateauing. It makes the invisible visible. Changes in breathing patterns, sleep habits, and stress management show up in HRV data within days to weeks.
What HRV doesn't tell you. HRV is a feedback tool. It reflects the state of your system. It doesn't train your system. Wearable devices that track HRV provide useful data. The data alone doesn't produce change. Regulation work — structured breathing practices, CO2 tolerance training, coached integration — is what shifts the baseline that HRV measures.
HRV is increasingly recognised as a reliable, non-invasive marker of autonomic nervous system function and resilience capacity.
SHAFFER & GINSBERG — AN OVERVIEW OF HRV METRICS, FRONTIERS IN PUBLIC HEALTH, 2017
BEYOND REGULATION
When the system stabilises, something else becomes available
A well-regulated nervous system is valuable on its own terms. Sleep improves. Reactivity decreases. Recovery between high-demand periods becomes faster. These are real, measurable gains.
They're also the prerequisite for something more structural.
When the autonomic baseline is stable, the conditions exist for what can be called integration — the alignment of cognitive clarity, intuitive signal, and coherent action under uncertainty. This is the capacity to make a complex decision and trust it. To stay present in a difficult conversation without bracing. To lead from actual clarity rather than from habit, performance, or override.
Why this matters practically. Under sustained pressure, most people default to one channel. Some become purely analytical — effective and disconnected from the felt sense of a situation. Some become reactive — responsive to emotional signals and unable to stabilise long enough to think clearly. Integration is the capacity to hold both: to think clearly while remaining present in the body, to act decisively while staying open to new information.
This capacity develops. It requires a stable regulatory foundation, structured practice, and — for most people — guided support in recognising their own patterns under pressure. That's the work.
BEYOND REGULATION
Practice, synthesis, integration
Everything I offer is built on the principles above. Respiratory physiology, autonomic regulation, and HRV-informed feedback are the mechanisms. Coaching and structured practice are the delivery.
I work with individual patterns. The starting point is always assessment — where your system is now, how it responds under load, where the gaps in your stress-recovery balance sit. From there, the work is tailored: breathing protocols, CO2 tolerance progressions, regulation practices under simulated and real-world pressure, and ongoing refinement informed by data and experience.
The science is the foundation. The application comes from 15 years of working with my own nervous system and learning — often the hard way — what produces lasting change.