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1 Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas, United States
2 Medicine, University of California San Diego, La Jolla, California, United States
3 Physical Medicine and Rehabilitation, University of Michigan Medical School, Ann Arbor, Michigan, United States
* To whom correspondence should be addressed. E-mail: ngonzale{at}kumc.edu.
After 7 generations (G7) of artificial selection of rats for running capacity, V o2max was 12 % greater in high capacity (HCR) than in low capacity runners (LCR). This difference was due to a greater O2 uptake and utilization by skeletal muscle of HCR, without differences between lines in convective O2 delivery to muscle by the cardio-pulmonary system (Vo 2max). The present study in generation 15 (G15) rats tested the hypothesis that continuing improvement in muscle O 2 transfer must be accompanied by augmentation in (Vo 2max to support Vo2max of HCR. Systemic O2 transport during maximal normoxic and hypoxic exercise was determined in HCR and LCR females. Vo2max divergence between lines increased due to both improvement in HCR and deterioration in LCR: normoxic V o2maxwas 50 % higher in HCR than LCR. The greater V o2maxin HCR was accompanied by a 41 % increase in Vo 2max: 96.1 ± 4.0 in HCR vs 68.1 ± 2.5 ml STPD O2.min-1.kg-1 in LCR (p<0.01), during normoxia, due to a 48% greater stroke volume than LCR. While tissue O2 diffusive conductance continued to increase in HCR, tissue O2 extraction was not different from LCR at G15, due to the offsetting effect of greater HCR blood flow. These results indicate that continuing divergence in Vo2max between lines occurs largely as a consequence of opposite changes in the capacity to deliver O2 to the exercising muscle.
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