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INTEGRATIVE |
1 Copenhagen Muscle Research Center, Rigshospitalet section 7652, Blegdamsvej 9, 2100 Copenhagen Ø, Denmark
2 Department of Sport Science, University of Århus, Denmark
3 Department of Physical Education, University of Las Palmas de Gran Canaria, Spain
The tight relation between arterial oxygen content and maximum oxygen uptake 
within a given person at sea level is diminished with altitude acclimatization. An explanation often suggested for this mismatch is impairment of the muscle O2 extraction capacity with chronic hypoxia, and is the focus of the present study. We have studied six lowlanders during maximal exercise at sea level (SL) and with acute (AH) exposure to 4100 m altitude, and again after 2 (W2) and 8 weeks (W8) of altitude sojourn, where also eight high altitude native (Nat) Aymaras were studied. Fractional arterial muscle O2 extraction at maximal exercise was 90.0 ± 1.0% in the Danish lowlanders at sea level, and remained close to this value in all situations. In contrast to this, fractional arterial O2 extraction was 83.2 ± 2.8% in the high altitude natives, and did not change with the induction of normoxia. The capillary oxygen conductance of the lower extremity, a measure of oxygen diffusing capacity, was decreased in the Danish lowlanders after 8 weeks of acclimatization, but was still higher than the value obtained from the high altitude natives. The values were (in ml min–1 mmHg–1) 55.2 ± 3.7 (SL), 48.0 ± 1.7 (W2), 37.8 ± 0.4 (W8) and 27.7 ± 1.5 (Nat). However, when correcting oxygen conductance for the observed reduction in maximal leg blood flow with acclimatization the effect diminished. When calculating a hypothetical leg 
at altitude using either the leg blood flow or the O2 conductance values obtained at sea level, the former values were almost completely restored to sea level values. This would suggest that the major determinant for 
not to increase with acclimatization is the observed reduction in maximal leg blood flow and O2 conductance.
(Received 2 February 2006;
accepted after revision 21 March 2006;
first published online 31 March 2006)
Corresponding author C. Lundby: Department of Sport Science, University of Århus, Katrinebjergvej 89C, 8200 Århus N, Denmark. Email: lundby{at}idraet.au.dk
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