We investigated the effect of a 21-day climbing expedition to 6,194 m on the oxygen uptake [Formula: see text] and leg blood flow (LBF) responses to submaximal exercise in five healthy, fit men during two-leg kicking exercise at 0-W and 50-W. Tests were completed 1 week before and 3 days after altitude acclimatization. The adaptation of [Formula: see text] at exercise onset was described by the time to 63% of the new steady state. Steady state [Formula: see text] during 50-W exercise was less post-climb (1290 ± 29 mL/min, mean ± SE) than pre-climb (1413 + 63 mL/min, P < .05). [Formula: see text] adapted more slowly at the onset of 50-W exercise post-climb. There were no differences in the steady state LBF during 50-W exercise, the increase above baseline, or the adaptation post-climb. Respiratory exchange ratio was greater at 50-W post-climb compared to pre-climb. Reduced steady state [Formula: see text] during exercise after exposure to high altitude is consistent with an increase in metabolic efficiency. Key words: work efficiency, leg blood flow, altitude, hypoxia, Doppler ultrasound