Early adopter here of McKeown’s approach. He came at it the same way i did – breathing exercises and especially controlled pauses after exhalation as an alternative therapy for asthma. All based off a Russian geriatric physician Buteyko back in the 70s.
Basic theory kinda boils down to breathing a little less. Close the mouth even while working out, (tape it shut at night if youre a mouth breather). I think the idea is that the body adapts to mild oxygen “hunger” with increased efficiency and improved oxygen uptake. It’s the Bohr Effect, apparently. (Low) Co2 levels are the limiting factor for oxygen uptake, not insufficient air/oxygen. Hyperventilation (over breathing) and the lower Co2 levels, are the problem.
10 years ago i started nose-breathing while working out. At first, i was gasping. Now I do Vo2 intervals nose-breathing only. I ride the Death Ride (at altitude) several times entirely nose breathing. During endurance training i routinely do short breath-holds after exhalation, to simulatie altitude supposedly.
Other mechanisms: biggest benefits from nose breathing may be from the blood vessel dilation caused by increased nitric oxide (concentrated in the nose). also, there’s some science to suggest reduced lactic acid, increased EPO, and what McKeown calls “psychological preparedness”. All matches my experience.
I’m 57. Vo2 over these years increased from like 48 to as high as 56, 57. And being asthma-free for the decade – it’s worth being a little loud (breathing) on the bike.