What You’ll Learn About Breathing, Stress, and Performance

• Why breathing patterns change under stress and how this affects energy, focus, and recovery.

• How the brain regulates breathing through CO₂ sensitivity, and why CO₂ tolerance improves oxygen delivery.

• Common signs of dysfunctional breathing (shallow, chest, or mouth breathing) that quietly add to stress.

• How breathing mechanics and posture influence resilience, energy, and emotional balance.

• The link between breathing, mitochondria, and endurance, and how oxygen efficiency shapes performance.

• Why breathing through your nose matters and how it boosts stress resilience

• Practical strategies to retrain breathing from coherence breathing and nasal breathing to advanced methods like Sport Masks and IHHT.

A science-led guide for professionals who want to understand stress differently and turn nervous system insights into a performance advantage.

This post is part of a larger piece about nervous system training for stress and performance.

Click here for: The Complete Guide to Nervous System Training for Stress and Performance

Why Breathing Shapes Stress and Performance

Learning how to breathe well gives us a simple, accessible way to manage stress and influence the nervous system. The world is a challenging place for the brain and nervous system, and how we breathe reflects how our body is handling those challenges.

Under stress, the sympathetic nervous system takes over, releasing stress hormones like adrenaline. One of the first changes is increased breathing rate, and breathing pattern shifts from slow, diaphragm-led breaths to faster, shallower chest breathing. The purpose is to bring in oxygen quickly and expel carbon dioxide so the brain and muscles have immediate fuel for action.

Breathing is mostly automatic, yet it can also be consciously controlled, making it a powerful gateway to health and performance. But dysfunctional breathing patterns often go unnoticed, and when they do, they can quietly add to stress levels.

Let’s look at what’s happening inside the body and how functional breathing can reset the system.

Breathing Is Regulated by the Brain

Your brainstem is constantly monitoring your blood chemistry, keeping track of:

• Carbon dioxide (CO₂)
• Oxygen (O₂)
• Blood pH

Contrary to common belief, it’s CO₂ levels that trigger breathing rather than O₂ levels. Even small increases CO₂ in your blood prompt your brain to make you breathe more, while oxygen levels have to drop much further to have the same effect.

Performance Insight: The better your body tolerates CO₂, the more efficiently your brain and muscles use oxygen.

Why This Matters Under Stress

When stressed or habitually mouth-breathing, we tend to over-breathe, taking in more oxygen than we need. This is part of the hyperventilation response and can show up as:

• Shallow breathing
• Chest breathing
• Mouth breathing
• “Anxiety breathing”
• Panic-style breathing

Even subtle over-breathing, whether from chronic stress, strong emotions, or long-term habits, lowers CO₂ levels too much, making symptoms worse (King, 1988).

There is a two way relationship between stress and breathing. Stress causes shallow breathing and shallow breathing causes stress.

CO₂: More Than a Waste Gas

We often think of carbon dioxide as something to “get rid of.” In reality, CO₂ plays a vital role in how your body uses oxygen.

Without enough CO₂:

• Oxygen can’t be properly released from hemoglobin (the Bohr effect).
• Cells and tissues are deprived of oxygen.
• You breathe more, but get less oxygen where it’s needed most.

This paradox explains why over-breathing reduces oxygenation rather than increases it, reduces energy and increases stress.

If you want to do an easy test to see how Co2 tolerant you are then you can learn more here:

• How to Do a BOLT Score Test and What it Means

Breathing Biomechanics: Muscles and Posture

Breathing relies on many muscles, but the diaphragm is the most important. Chronic stress often creates muscular tension and postural changes that restrict its movement. Over time, we adapt to these restrictions and lose awareness of how inefficient our breathing has become. Habits such as frequent sighing, shallow or rapid breaths, excessive yawning, mouth breathing, or lifting shoulders when breathing,  are all signs that stress has altered breathing patterns in ways that undermine efficiency and resilience.

In practice, the most common patterns are:

• Breath holding
• Shallow/chest breathing with minimal diaphragm motion
• Paradoxical breathing (abdomen pulls inward on inhale)
• Mouth breathing
• Hyperventilation (excess rate or volume)
• Muscle tightness around the thoracic cage, abdomen, back, and shoulders
• Clavicular/shoulder breathing (lifting shoulders to inhale)

All of these patterns reduce breathing volume and efficiency, maintaining stress.

To restore better breathing involves inhaling more slowly and effectively, while strengthening the core, so postural muscles provide support, without over-recruiting and tightening muscles that should remain flexible for breathing.

The Role of Nasal Breathing in Performance

Breathing through the nose does more than filter and warm the air, it also stimulates the release of nitric oxide in the nasal passages. Nitric oxide is a powerful signalling molecule that promotes vasodilation, widening blood vessels and improving circulation. This enhances oxygen delivery to tissues and supports mitochondrial efficiency.

Nasal breathing not only slows and stabilises breathing but also boosts cardiovascular function, energy production, and resilience under stress by increasing parasympathetic nervous system activity.

The Hidden Problem of Mouth Breathing at Work
Even those who consider themselves “nose breathers” can easily slip into mouth breathing during long conversations, meetings, or public speaking. Mouth breathing bypasses nitric oxide production, reduces oxygen efficiency, and reinforces stress physiology in the long term.

Becoming aware of these moments and deliberately returning to nasal breathing helps maintain CO₂ tolerance and steadier energy. A simple strategy is to pace your speech, pause between phrases to take a calm breath through the nose, which helps to deliver at a clearer pace and protect against stress.

Coherence Breathing For Stress Management

Coherence breathing is a practice of slowing the breath to around 5–6 breaths per minute, creating a balanced rhythm between inhalation and exhalation. This pace synchronises heart rate, breathing, and blood pressure in a state known as cardiorespiratory coherence. The result is increased vagal tone, improved heart rate variability (HRV), and more efficient oxygen delivery. Practised regularly, coherence breathing trains the nervous system, lowers stress reactivity, and enhances focus, recovery, and emotional regulation. It also offers a simple way to pause during a busy day, shift out of sympathetic arousal, and restore balance, making it a powerful tool for sustained performance.

Breathing, Mitochondria, and Energy

Shallow breathing limits oxygen delivery to cells, reducing mitochondrial energy production. Over time, this oxygen shortage weakens mitochondrial function and lowers overall cellular energy.

That means:

• Lower energy output
• Poorer stress adaptability
• Increased fatigue and slower recovery

Cumulatively, dysfunctional breathing erodes resilience at both the cellular and psychological levels.

Curious about the relevance of mitochondria to stress resilience and performance? You can read more in the blog Post: Mitochondrial Health: The Key to Sustained Energy

Summary: Breathing for Stress Resilience and Performance

Breathing is both automatic and trainable, making it a powerful gateway to health and performance. Under stress, breathing often shifts into shallow, chest-driven patterns that reduce CO₂ tolerance, limit oxygen delivery, and weaken mitochondrial energy production. The result is fatigue, reduced resilience, and slower recovery.

Restoring functional breathing, slower, depper, diaphragm-led, and nasal, rebuilds CO₂ tolerance, strengthens breathing muscles, and supports mitochondrial efficiency. Together, these changes enhance focus, recovery, and long-term performance.

About BodyMindBrain:

At BodyMindBrain, we help high-performing professionals break free from the cycle of stress and fatigue. Modern lifestyles often over-activate the sympathetic nervous system, increasing the adaptive load and leaving too little time for recovery and balance.

Using advanced, science-backed technologies, we optimise brain function, improve oxygen efficiency, mitochondrial health and build physical strength. Alongside we help you re-establish lifestyle habits and psychology that support recovery. The result is sustainable resilience: the ability to perform at your best without sacrificing long-term wellbeing.