I have been instructed to breathe in and out through the nose, but some have said breathe out through the mouth, however, it would seem that only nose breathing is better for recovery?

You just finished a hard workout, your heart’s racing, your muscles are screaming, and the first instinct kicks in: open your mouth and take big, forceful breaths.

It feels like you’re feeding your body the oxygen it needs.

But physiologically, you might be doing the exact opposite.

There is a mechanism central to performance and recovery: the Bohr effect, which explains why trying to expel too much carbon dioxide interferes with your ability to deliver oxygen where it’s needed.

Why do we do this? 

Because our bodies evolved to associate rapid breathing with escaping danger — a primal response hardwired into our nervous system. In a fight-or-flight state, the brain prioritises survival over efficiency. But this ancient reflex doesn’t always match modern stressors like intense training, where the goal is recovery, not escape.

Carbon dioxide is not the enemy. It’s the key.

Contrary to popular belief, carbon dioxide (CO₂) isn’t just a waste product. It’s a critical component in how your body regulates oxygen release at the cellular level.

Oxygen travels in your blood bound to haemoglobin. But haemoglobin only releases that oxygen when CO₂ levels in the surrounding tissue signal the need.

This is the Bohr effect, described over a century ago but still overlooked in breathing practices.

In conditions where CO₂ and hydrogen ion concentration (H⁺) are high — such as in actively working muscles — haemoglobin’s affinity for oxygen decreases, allowing oxygen to dissociate and be delivered where it’s needed most.

But if you reduce CO₂ too quickly — which is precisely what happens during hyperventilation — you raise blood pH, and haemoglobin holds on to the oxygen.

The result? Your blood might be full of oxygen, but your cells are starving. When you over-breathe, you’re not oxygenating — you’re undermining your own performance.

Low CO₂ disrupts:

• Oxygen delivery to tissue

• Diaphragmatic activation and control

• Autonomic nervous system regulation

• Blood flow to the brain and muscles

This can create a downward spiral: the more you over-breathe, the more stressed and fatigued you feel — and the more you over-breathe.

The fix is not more air — it’s better control.

Here’s how:

• Close your mouth. This instantly slows the breath and retains more CO₂.

• Breathe through your nose.

• Let the diaphragm lead. Shallow chest breathing reinforces panic signals. Deep, diaphragmatic breath activates recovery.

• Slow your exhale.

• Pause briefly at the end of the exhale. This gives CO₂ a chance to accumulate and restore balance.

What you’re building is CO₂ tolerance — the ability to maintain function even when CO₂ is elevated. And that directly translates to greater oxygen delivery, better focus, and faster recovery.