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Carbohydrate utilization during exercise after high-altitude acclimation: a new perspective

G B McClelland1, P W Hochachka, J M Weber

  • 1Department of Zoology, University of British Columbia, Vancouver, BC, Canada V6T 1Z4. mcleland@unixg.ubc.ca

Proceedings of the National Academy of Sciences of the United States of America
|August 26, 1998
PubMed
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High altitude (HA) exercise doesn't increase carbohydrate use despite its efficiency. Exercise intensity, not altitude acclimation, is the main factor determining fuel selection for athletes.

Area of Science:

  • Exercise Physiology
  • Altitude Physiology
  • Metabolic Biochemistry

Background:

  • Carbohydrate (CHO) is considered the preferred fuel at high altitude (HA) due to its higher ATP yield per O2 molecule.
  • Limited data exist on how HA acclimation affects substrate utilization during exercise.
  • Understanding fuel selection is crucial for optimizing athletic performance in hypoxic environments.

Purpose of the Study:

  • To determine total carbohydrate and circulatory glucose utilization during exercise in HA-acclimated and sea-level (SL) rats.
  • To test the hypothesis that the percentage of CHO contribution to total metabolism (VO2) is determined by exercise intensity relative to maximal oxygen uptake (% VO2max).

Main Methods:

  • Indirect calorimetry was used to measure oxygen consumption (VO2).

Related Experiment Videos

  • Infusions of D-[6-3H]glucose were employed to track circulatory glucose utilization.
  • Rats were acclimated to HA (hypoxia, FIO2 = 0.12) or studied at sea level (SL) and exercised at 60% and 80% of their respective VO2max.

    • Main Results:

    • HA rats exhibited a lower VO2max compared to SL rats (67.55 +/- 1.26 vs. 89.30 +/- 1.23 ml kg-1 min-1).
    • At 60% VO2max, both HA and SL rats utilized similar percentages of CHO (38% +/- 3% and 38% +/- 5%, respectively).
    • At 80% VO2max, CHO contribution increased significantly in both groups (54% +/- 5% in HA, 59% +/- 4% in SL).
    • Circulatory glucose and muscle glycogen provided consistent proportions of energy (approx. 20% and 18% of VO2, respectively) in both conditions.

    Conclusions:

    • HA acclimation does not enhance the relative contribution of CHO to energy production during exercise.
    • The O2-saving advantage of CHO is counteracted by limited CHO stores at HA.
    • Relative exercise intensity, rather than HA acclimation, is the primary determinant of metabolic fuel selection during exercise.