Andrew Huberman· PhD
For people who don't tolerate carbon dioxide very well, they don't have very good phrenic, that is, neuromechanical control of the diaphragm, for whatever reason-- again, it doesn't mean you're not fit. It just means you don't have or you have not yet developed neuromechanical control of the diaphragm. It would be near impossible for you to do box breathing for two or three minutes with eight seconds in, eight seconds hold, eight seconds exhale, eight second hold.