Breathing While Running: Techniques and Common Myths

"Breathe in through your nose, out through your mouth." If you're new to running, you've almost certainly heard this advice at least once. But is it really accurate? Breathing during running is a topic where popular beliefs often clash with scientific evidence, sometimes with a surprising gap between the two. Here, I'll review the main questions we all have about our breathing, based on my research and experience — without being dogmatic.

Nasal vs. Mouth Breathing: The False Dilemma

Arguments for Nasal Breathing

Exclusive nasal breathing has its fans. And the theoretical advantages are real: air inhaled through the nose is filtered (dust, allergens), warmed, and humidified before reaching your lungs. The nose also produces nitric oxide (NO), a vasodilator that could improve gas exchange. Based on my research, some studies show that runners trained to breathe through their nose develop better ventilatory efficiency at low intensity over several weeks.

Limitations of Nasal Breathing

The main issue is physical: your nostrils create approximately two to three times more airflow resistance than your mouth. Beyond 60-70% of your MAS, the oxygen demand exceeds what your nose alone can supply. Forcing nasal breathing at high intensity makes your diaphragm work harder, increases your perceived exertion, and can even decrease your performance.

In practice, most of us spontaneously adopt mixed breathing — nasal at rest and low intensity, gradually shifting to mouth breathing as we speed up. This is probably the most natural and effective strategy.

Breathing Rhythms: 2:2, 3:2, or Instinct?

Your breathing rhythm refers to the number of steps you take during inhalation and exhalation. The most commonly cited patterns include:

• 3:3 — three steps inhaling, three steps exhaling. Suitable for easy jogging and warm-ups.
• 2:2 — the most common for easy runs and marathon pace.
• 2:1 or 1:1 — for intense effort, near or above your anaerobic threshold.
• 3:2 — an asymmetrical rhythm that alternates the foot striking the ground during exhalation, which is thought to distribute diaphragmatic stress more evenly.

The Asymmetrical Rhythm: An Appealing Idea

The 3:2 (or 2:1) rhythm was popularized by coach Budd Coates and is based on interesting logic: if you always exhale on the same foot strike, your diaphragm consistently relaxes on the same side, potentially creating a mechanical imbalance. Alternating is believed to distribute forces better. However, direct scientific evidence for this benefit is scarce. No serious study has demonstrated that an asymmetrical rhythm prevents injuries or truly improves performance.

Should You Force a Rhythm?

Good question. For an experienced runner, breathing rhythm automatically adjusts to the intensity of the effort. Forcing yourself to follow an artificial pattern can be mentally taxing and disrupt the fluidity of your stride. However, if you're a beginner and consistently hyperventilate, becoming aware of your breathing and attempting a slower rhythm (3:3 or 2:2) can be a useful tool to regulate your pace — especially in the first few minutes of a run, when we all tend to start too fast.

Hyperventilation: When Your Breathing Goes into Overdrive

Hyperventilation occurs when you breathe too much relative to what your body actually needs. This leads to a drop in blood CO₂ (hypocapnia), which paradoxically causes shortness of breath, tingling in the fingers, and sometimes dizziness. While running, this often happens in two situations:

• Starting too fast: You abruptly exceed your ventilatory threshold, and your body reacts with a disproportionate increase in breathing rate.
• Pre-race stress: Anxiety activates your sympathetic nervous system, which speeds up your ventilation even before the starting gun.

The solution is simple in theory, harder in practice: slow down, lengthen your exhalation (it should last at least as long as your inhalation), and focus on a stable rhythm. Knowing your training paces helps you calibrate your effort from the very first steps.

Diaphragmatic Breathing: Useful or Overrated?

Diaphragmatic breathing (or belly breathing) involves engaging your diaphragm rather than your intercostal muscles and shoulders to inhale. This allows for a larger air volume per breath cycle, which reduces breathing frequency for the same airflow. The benefits are well-documented:

• Better ventilation of the lung bases (the area richest in capillaries).
• Less tension in the shoulders and neck.
• Better energy efficiency (your diaphragm is more efficient than accessory muscles).

That said, during intense effort, accessory muscles are inevitably recruited — and that's normal. Diaphragmatic breathing is a valuable tool at low to moderate intensity, but personally, don't expect to maintain it while running a 1500m at full speed. Practicing it at rest and during easy runs is the best way to integrate it naturally.

Side Stitches: The Persistent Mystery

Despite decades of research, the exact mechanism of a side stitch (ETAP — exercise-related transient abdominal pain) isn't fully understood. Several hypotheses coexist:

• Irritation of the parietal peritoneum: Repetitive movements are thought to create friction between the peritoneal layers — which would explain why side stitches are more frequent in sports with vertical impacts.
• Diaphragmatic spasm: An older hypothesis, somewhat questioned because the pain isn't always located in the diaphragm area.
• Transient ischemia of the diaphragm: Blood would be diverted to the leg muscles at the expense of the diaphragm.

What seems to reduce the risk:

• Avoid eating a large meal two to three hours before your run.
• Warm up gradually rather than starting too fast.
• Strengthen your core (plank exercises).
• Lengthen your exhalation within your breathing rhythm.

If you get a side stitch while running, slow down, exhale deeply while pressing on the painful area, and lean your torso slightly to the opposite side. Personally, this almost always works.