Arterial O2 saturation (Sa(O2)) decreases in hypoxia in the transition from rest to moderate exercise, but it is unknown whether over several weeks at high altitude Sa(O2) in submaximal exercise follows the same time course and pattern as that of ventilatory acclimatization in resting subjects. Ventilatory acclimatization is essentially complete after ~1 wk at 4,300 m, such that improvement in submaximal exercise Sa(O2) would then require other mechanisms. On days 2, 8, and 22 on Pikes Peak (4,300 m), 6 male subjects performed prolonged steady-state cycle exercise at 79% maximal O2 uptake [V̇(O(2 max))]. Resting Sa(O2) rose from day 1 (78.4 ± 1.6%) to day 8 (87.5 ± 1.4%) and then did not increase further by day 20 (86.4 ± 0.6%). During exercise, Sa(O2) values (mean of 5-, 15-, and 30-min measurements) were 72.7% (day 2), 78.6% (day 8), and 82.3% (day 22), meaning that all of the increase in resting Sa(O2) occurred from day 1 to day 8, but exercise Sa(O2) increased from day 2 to day 8 (5.9%) and then increased further from day 8 to day 22 (3.7%). On day 22, the exercise Sa(O2) was higher than on day 8 despite an unchanged ventilation and O2 consumption. The increased exercise Sa(O2) was accompanied by decreased CO2 production. The mechanisms responsible for the increased exercise Sa(O2) require further investigation.
ASJC Scopus subject areas
- Physiology (medical)