A revision of maximal oxygen consumption and exercise capacity at altitude 70 years after the first climb of Mount Everest

On the 70th anniversary of the first climb of Mount Everest by Edmund Hillary and Tensing Norgay, we discuss the physiological bases of climbing Everest with or without supplementary oxygen. After summarizing the data of the 1953 expedition and the effects of oxygen administration, we analyse the reasons why Reinhold Messner and Peter Habeler succeeded without supplementary oxygen in 1978. The consequences of this climb for physiology are briefly discussed. An overall analysis of maximal oxygen consumption (VO2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$) at altitude follows. In this section, we discuss the reasons for the non-linear fall of VO2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ at altitude, we support the statement that it is a mirror image of the oxygen equilibrium curve, and we propose an analogue of Hill's model of the oxygen equilibrium curve to analyse the VO2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ fall. In the following section, we discuss the role of the ventilatory and pulmonary resistances to oxygen flow in limiting VO2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$, which becomes progressively greater while moving toward higher altitudes. On top of Everest, these resistances provide most of the VO2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ limitation, and the oxygen equilibrium curve and the respiratory system provide linear responses. This phenomenon is more accentuated in athletes with elevated VO2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$, due to exercise-induced arterial hypoxaemia. The large differences in VO2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ that we observe at sea level disappear at altitude. There is no need for a very high VO2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ at sea level to climb the highest peaks on Earth. imageAbstract figure legend Maximal oxygen consumption (VO2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$) shows a non-linear fall with altitude that is a mirror image of the oxygen equilibrium curve. Di Prampero and Ferretti were the first to associate the non-linear behaviour of the respiratory system to the oxygen equilibrium curve. On the other hand, Wagner constructed his convective curve accounting for the effects of the oxygen equilibrium curve. The decrease is more accentuated in athletic subjects with elevated VO2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ compared to those who are non-athletic, so that the large differences in VO2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ that are observed at sea level disappear at altitude. Such consequences are due to the effect of ventilatory and pulmonary resistances to oxygen flow in limiting VO2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$, which becomes progressively greater while moving toward higher altitudes compared to that of the cardiovascular resistance. On top of Everest, the pulmonary resistances provide most of the VO2max${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ limitation and the respiratory system provides linear responses. image