Steady state and kinetic response of VO2 and leg blood flow following a 21 day expedition to 6200 M

VO2 and leg blood flow (LBF) kinetics were assessed in 5 males (age: 28 ± 2 y: and ht: 173.7 ± 3.0 cm, mean ± SE) one week before and 3 days after a 21-day climb to the summit of Mt. Denali, Alaska (6200 m). Body mass and cycling VO2 max were not different pre and post-climb (BM = 76.9 ± 3.7 vs 75.5 ± 2.9 kg; VO2 max = 52.3 ± 2.1 vs 50.6 ± 1.9 ml/kg/min). VO2 and LBF kinetics were assessed by the mean response time (MRT, time to 63% of the steady state response) of the increase in VO2 and LBF during a step increase from loadless to 50 W leg extension exercise on a kicking ergometer. Continuous measures of femoral artery mean blood velocity (pulsed Doppler), diameter (echo. Doppler), and VO2 were collected. LBF was calculated from the beat-by-beat mean blood velocity and arterial diameter. Increases in VO2 and LBF from baseline to steady state were smaller (P<0.05) post-climb (VO2: pre 517.8 ± 39.8 vs post 426.6 ± 16.4 ml/min, LBF: pre 1187.6 ± 115.1 vs post 951.5 ± 82.4 ml/min). This resulted in a lower (P<0.05) steady-state VO2 post-climb (VO 2: pre 1405.5 ± 62.8 vs. post 1281.1 ± 26.6 ml/min). LBF kinetics were not different between pre and post. VO2 kinetics were slower (P<0.05) post-climb (MRT: pre 38.0 ± 4.5 vs post 43.8 ± 4.5 s). The lower steady-state VO2 and slower kinetics might suggest an altered metabolic efficiency during submaximal exercise after exposure to high altitude.