Maximal oxygen consumption in healthy humans: theories and facts.

his article reviews the concept of maximal
oxygen consumption (VO2max) from the perspective of multifactorial
models of VO2max limitation. First, I discuss procedural
aspects of VO2max measurement: the implications
of ramp protocols are analysed within the theoretical work
of Morton. Then I analyse the descriptive physiology of
VO2max, evidencing the path that led to the view of monofactorial cardiovascular or muscular VO2max limitation.
Multifactorial models, generated by the theoretical work of
di Prampero and Wagner around the oxygen conductance
equation, represented a radical change of perspective. These
models are presented in detail and criticized with respect to
the ensuing experimental work. A synthesis between them is
proposed, demonstrating how much these models coincide
and converge on the same conclusions. Finally, I discuss
the cases of hypoxia and bed rest, the former as an example
of the pervasive effects of the shape of the oxygen equilibrium
curve, the latter as a neat example of adaptive changes
concerning the entire respiratory system. The conclusion
is that the concept of cardiovascular VO2max limitation is
reinforced by multifactorial models, since cardiovascular
oxygen transport provides most of the VO2max limitation,
at least in normoxia. However, the same models show that
the role of peripheral resistances is significant and cannot
be neglected. The role of peripheral factors is greater the smaller is the active muscle mass. In hypoxia, the intervention
of lung resistances as limiting factors restricts the role
played by cardiovascular and peripheral factors.