The Science of Breathing: How Your Breath Controls Your Nervous System

The Science of Breathing (and Why How You Breathe Matters)

This week’s Better You, Backed by Science is about the science of breathing, and how a longer exhale – and even a breath hold – can be healthy.

We all breathe.

But according to science, what really matters is how you breathe.

Breathe slowly, for example, and you can help your body relax, reduce blood pressure, and even enter a state of calm alertness.

Why?

Because slow breathing stimulates your vagus nerve.

How breathing affects your nervous system

When you inhale, special cells in your lungs — called stretch receptors — detect the expansion of your lungs.

They convert that stretch into electrical signals, which travel up your vagus nerve to the brain.

Once those signals reach the brain, something interesting happens:

the brain briefly eases off vagus nerve activity to the heart.

What does that do?

Your heart rate speeds up.

Let me explain.

The vagal brake

The vagus nerve acts as the body’s primary brake on heart rate.

Think of a car with two brakes:

• the foot brake (the main brake)
• and the handbrake (a secondary one)

The vagus nerve is like the foot brake on your heart.

When you inhale, vagus nerve activity to the heart temporarily eases — the brake is slightly released — so your heart rate rises.

When you exhale, vagus nerve activity increases again.

The brake is reapplied.

Your heart rate slows.

This natural rhythm is known as respiratory sinus arrhythmia — and it’s a sign of a healthy nervous system.

The secret behind breathing techniques

The secret to breathing techniques is simple:

Maximise vagus nerve activation.

We do this by slowing the breath and, in particular, lengthening the exhale.

That’s why so many breathing practices — including those taught in ancient traditions for thousands of years — emphasise a longer exhale.

Why does this matter?

Because regularly activating the vagus nerve is a bit like exercising a muscle.

Go to the gym regularly and you build muscle tone.

Stimulate the vagus nerve regularly and you build vagal tone — a term that roughly reflects how responsive and resilient your nervous system is.

And high vagal tone is associated with a long list of benefits, including:

• improved cardiovascular health
• better digestive function
• reduced inflammation and healthier immune regulation
• greater nervous system balance
• protective effects on mental health (lower risk of anxiety and depression)
• improved cognitive function
• increased lifespan

All from something as simple as breathing more slowly — especially on the exhale.

Pretty remarkable.

The added power of breath holds

There’s even more we can gain by consciously shaping the breath.

Some techniques add a short breath hold — and this delivers additional benefits.

The science of box breathing

Techniques like box breathing (inhale 4s, hold 4s, exhale 4s, pause 4s) or the 4-7-8 method include a brief breath hold.

This does two important things.

First, the breath hold directly stimulates the vagus nerve, helping reduce heart rate and blood pressure — encouraging a calm state.

Second, holding the breath causes a temporary rise in carbon dioxide in the blood.

That sets off a helpful sequence:

1. Blood acidity rises slightly
2. Haemoglobin loosens its grip on oxygen
3. More oxygen becomes available to the brain

The result?

A state of calm focus — relaxed, yet alert.

This combination is likely one reason box breathing is used by Navy SEALs.

With regular practice, something else happens too: the brain’s threat centre (the amygdala) becomes less reactive to carbon dioxide.

In other words, the brain learns that rising CO₂ isn’t dangerous — which helps us stay calm under pressure, stress, or challenge.

Try This (box breathing and the 4-7-8 breath)

Try box breathing for 5 minutes a day over the next week.

1. Sit comfortably and notice your breath for a minute
2. Inhale slowly for a count of 4
3. Hold for 4
4. Exhale for 4
5. Pause for 4
6. Repeat for around 5 minutes

If you’d like to go further, try 4-7-8 breathing — which slows the breath to about three cycles per minute.

1. Inhale for 4
2. Hold for 7
3. Exhale for 8
4. Repeat for around 5 minutes

Whether you breathe out through your nose or mouth is less important — both work. Choose what feels most comfortable.

What to dive deeper?

🎥 I explore the science of breathing techniques in more detail — and guide you through two short box breathing exercises — in my YouTube video.

References (if you’re curious)

• Slow breathing uses the vagus nerve to increase and decrease heart rate. Link here
• Longer exhalations stimulate the vagus nerve. Link here
• Psychology Today piece on how longer exhalations hack the nervous system. Link here
• Benefits of high vagal tone. Link here
• Benefits of 4-7-8 breathing. Link here

More

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