Why bother
Nasal breathing humidifies and warms air, releases nitric oxide that improves oxygen uptake, and forces a lower, more efficient breath rate. The trade-off is a slower pace at first.
The 6-week plan
Weeks 1–2: nose-only at conversation pace, walks if needed. Weeks 3–4: nose-only easy runs, mouth allowed on hills. Weeks 5–6: nose-only most of every run, mouth only above threshold.
Pace expectations
Expect to be 30–60 seconds per km slower for the first 3–4 weeks. Most runners return to their original pace by week 8, with lower perceived effort and a lower max heart rate at the same speed.
When to open your mouth
Final 10% of an interval, race finish, very steep hill. Otherwise, stay nasal — the adaptation is what you are training.
Log your sessions in Breathe On and explore the matching guidance at [/breathing-for/athletic](/breathing-for/athletic).