Runfluencers are flooding social feeds with one simple command: Breathe through your nose. Meredith Dietz, senior staff writer at Lifehacker , traces the pushback to James Nestor’s 2020 book Breath . Modern life, they argue, has wired us wrong. We’ve forgotten nasal breathing. And running? That’s ground zero for the debate. Nose breathing slows your rate. It builds CO2 tolerance. Mouth breathing dumps carbon dioxide too fast. Result: that frantic “can’t catch my breath” panic mid-stride. Studies back this. A recent paper in Respiratory Medicine and Research shows nasal breathing during cardio holds merits, improving efficiency in low-intensity zones ([source](https://www.sciencedirect.com/science/article/pii/S2950273X25000463)). Runners stay conversational. They linger in Zone 2, the aerobic sweet spot for base-building. But push harder. Tempo runs. Intervals. Oxygen demand spikes. The nose can’t keep up. Its airway is narrower. Forcing it? Performance tanks.…