Fig. 4. _O2max at high altitude drops considerably in response to reduced arterial oxygen content. Here, _O2max is shown for sea-level sojourners at 3790m altitude and for high-altitude natives at 3600m (filled columns). _O2max increases in both groups of subjects when they are given supplemental O₂ equal to sea-level normoxia levels (open columns). However, the increase in sojourners (38%) is over four times that of the high-altitude natives (8%) (data from Cymerman et al., 1989; Favier et al., 1995). Values are means + S.E.M., N=8 (Cymerman), N=11 (Favier).