Nasal Breathing vs Mouth Breathing During Exercise: What Science Says

For decades, athletes were told to breathe however felt natural. A growing body of research now suggests nasal breathing — even during moderate-to-hard effort — offers measurable performance advantages worth training for.

The Physiological Differences

Nasal breathing: filters, warms, and humidifies air; produces nitric oxide; promotes slower deeper breathing; maintains higher CO2 for better O2 offloading; activates the parasympathetic nervous system. Mouth breathing: allows higher max airflow volume; produces no nitric oxide; promotes faster shallower breathing; lowers CO2, reducing O2 availability at tissues; activates the sympathetic system.

What the Research Shows

A landmark study by Morton et al. found nasal breathing during sub-maximal exercise produced similar performance outcomes to mouth breathing with significantly lower perceived exertion and heart rate. Research on nasal nitric oxide consistently shows improved pulmonary oxygen uptake and reduced vascular resistance with nasal breathing.

The Lactate Threshold Connection

Nasal breathing forces athletes below the ventilatory threshold — the intensity where CO2 accumulation triggers a shift to faster mouth breathing. Training at this threshold with nasal breathing improves lactate threshold over time, the most trainable determinant of endurance performance.

When Mouth Breathing Is Necessary

Above ~70-80% of VO2 max, nasal breathing typically can't meet ventilation demands. The goal is maximising nasal breathing time below this threshold. HiStrips extend that range by reducing nasal resistance.

FAQ

Will switching to nasal breathing make me slower at first?

Yes — for 2-4 weeks as you adapt. After adaptation, performance returns to baseline or improves with significant long-term gains.

Should I nasal-breathe in races?

At moderate paces (marathon, half-iron, endurance events) yes. At sprint distances, switch as needed.

How do nasal strips help with the transition?

HiStrips reduce the effort required, making the adaptation period easier and the long-term practice more sustainable.

Train your most important system. HiStrips.