Diaphragm and cortisol

Today I’d like to explain a bit more about our fantastic muscle: the diaphragm, and its connection to cortisol.

Your diaphragm does more than help you breathe: it directly influences your stress hormone levels. The mechanism always comes back to our fight-or-flight response.

When you breathe shallowly (chest-dominant breathing), your body speaks directly to your amygdala, and the amygdala listens, reading it as a low-grade threat signal.

The HPA axis (hypothalamic-pituitary-adrenal) responds by maintaining elevated cortisol secretion, the primary stress hormone.

Correct diaphragmatic breathing, on the other hand, works differently.

The downward mechanical movement of the diaphragm on each inhale stimulates vagal afferents, the sensory fibres of the vagus nerve running alongside the diaphragm. This activates the parasympathetic branch of the autonomic nervous system, which in turn inhibits HPA axis activity and reduces cortisol output.

Slow diaphragmatic breathing (around 6 breaths a minute) maximizes baroreflex gain and increases heart rate variability (HRV): two reliable markers of healthy parasympathetic tone and cortisol regulation capacity.

In short: the way you breathe is not just a passive reflex. It is an active, trainable input into your neuroendocrine system.

How often during your day do you actually breathe this way?

Want to feel the difference?

Try this for 5 minutes:

• Inhale slowly through the nose for 5 seconds: let your ribcage expand first, while the upper chest stays relatively still.
• Exhale slowly for 5 seconds: let the ribcage return to its natural position.
• Keep a smooth, unforced rhythm.

This is one of the first things I work on with every client, because everything else builds on top of it.