I have wondered many times as others about O2 delivery to the mascles as many other posters and it males lots of sense especially suprafisiological O2 carryng-capacity as well as Blood doping. HOwver those do not happen under normal situation and then are not considered physiological. Being devils advocate, if I were too skini and low VO2max but could replicate huge muscle power in my legs I could be the man....regardless of my VO2max,
On the other hand McArdle´s diseases is a disease where the muscle lacks of muscle posphorilasa which inhinits glycogen breakdaown and therefore glycolytiv pathway. Therefore highly liming exercise performance, regardless that ventilatory thresholds are found similar in normal subjects or McArdle´s. That is another Non-Physiological condition, but also as in the opposite exapmle of O2 delifery, muscle metabolism es very important and to, me probably the limiting factor.
IN the 70, 80, and low 90´s Cardiorespiratory physiological adaptations came down to lung capacity, cardiac output, capilarisation, VO2max...However moder physiology has turned into Exercise biochemistry and muscle metaolism, since what we are looking at now is at the cell and all the events occuring there, many of which are still unknown and the direction as that it seems that the limiting facto could be in that pathway. About CArdiorespiratory physiology and adaptations we know many things but not meny about events at the cellular level.
I believe there is not a single cause. Many of the cause we are talking a bout are a "requisite" to be elite, but Science still has not rovided the answer, althou moder studies are following the muscular metabolism pathway.
Cheers.