We investigated the effect of a 21-day climbing expedition to 6,194 m on the oxygen uptake (V022) and leg blood flow (LBF) responses to submaximal exercise in five healthy, fit men during two-leg kicking exercise a 0-W and 50-W. Tests were completed 1 week before and 3 days after altitued acclimatization. The adaptation of VO2 at exercise onset was described by the time to 63% of the new steady state. Steady state VO2 during 50-W exercise was less post-climb (1290+/- 29 mL/min, mean +/- SE) than pre-climb (1413+/- 63 mL/min, P <.05). VO2 adapted more slowly at the onset of 50-W exercise post climb. There were no differences in the steady state LBF during the 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 V02 during exercise after exposure to high altitude is consistent with an increase in metabolic efficiency.