High-altitude Tibetans undergo a pattern of adaptations to chronic hypoxia characterized, among others, by a more efficient aerobic performance compared to acclimatized lowlanders. To test whether such changes may persist upon descent to moderate altitude, oxygen uptake of 17 male Tibetan natives lifelong residents of 3,500-4,500 m was assessed within one month upon migration to 1,300 m. Exercise protocols were: 5-min treadmill walking at 6 km h-1 on increasing inclines from +5% to +15% and 5-min running at 10 km h-1 on a +5% grade. The data (mean ± SE) were compared with those obtained on Nepali lowlanders. When walking on +10%, +12.5% and +15%, net VO2 of Tibetans was 25.2 ± 0.7, 29.1 ± 1.1, and 31.3 ± 0.9 ml kg-1 min-1, respectively, i.e. 8%, 10%, and 13% less (P<0.05) than that of Nepali. At the end of the heaviest load, blood lactate concentration was lower in Tibetans than in Nepali (6.0 ± 0.9 vs. 8.9 ± 0.6 mM; P< 0.05). During running, VO2 of Tibetans was 35.1 ± 0.8 vs. 39.3 ± 0.7 ml kg-1 min-1 (i.e. 11% less; P<0.01). In conclusion, during submaximal walking and running at 1,300 m, Tibetans are still characterized by lower aerobic energy expenditure than control subjects that is not accounted for by differences in mechanical power output and/or compensated for by anaerobic glycolysis. These findings indicate that chronic hypoxia induces metabolic adaptations whose underlying mechanisms still need to be elucidated, that persist for at least one month upon descent to moderate altitude.