Dallam & Kies 2020, nasal versus oral and oronasal breathing during exercise (review)

Narrative review of nasal breathing during exercise. It reports that nasal breathing raises airway resistance, slows breathing frequency and may improve ventilatory efficiency, but notes plainly that these effects have been infrequently examined and the literature is thin. Useful as an honest summary of the state of the evidence: proposed mechanisms exist, but direct evidence of a performance benefit does not. Written by the same lead author as the 2018 nasal-breathing study, so its framing carries a prior in favour of nasal breathing and should not be overstated.