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Acute Hypoxia Decreases Maximum Fat Oxidation Rate During Step Incremental Exercise Normalized to Respiratory
Youmna Elsayed Hassanein1, Dania Ibrahim1, Juan M Murias1
1College of Health and Life Sciences, Hamad Bin Khalifa University, Doha, Qatar.
European Journal of Sport Science
|January 11, 2026
Summary
Hypoxia significantly reduces fat oxidation (FATox) and maximal fat oxidation rate (MFO) during exercise, even when exercise intensity is normalized. This suggests hypoxia directly impacts fuel selection during physical activity.
Area of Science:
- Exercise Physiology
- Environmental Physiology
- Nutritional Biochemistry
Background:
- Fat oxidation (FATox) during exercise is crucial for energy metabolism.
- The impact of hypoxia on FATox and maximal fat oxidation rate (MFO) remains unclear due to varied research protocols.
Purpose of the Study:
- To investigate the effects of normobaric hypoxia on substrate utilization during exercise.
- To determine the impact of hypoxia on maximal fat oxidation rate (MFO).
Main Methods:
- Seventeen active adults underwent incremental exercise tests in normoxia and hypoxia.
- Indirect calorimetry measured cardiorespiratory responses and substrate utilization.
- Respiratory compensation point (RCP) normalized exercise intensity relative to maximal capacity.
Main Results:
- Hypoxia decreased FATox across all exercise intensities (p < 0.001).
- Maximal fat oxidation rate (MFO) was reduced by 22% in hypoxia (p < 0.001).
- MFO occurred at a similar percentage of VO2max in both conditions, suggesting a direct effect of hypoxia on fuel selection.
Conclusions:
- Normobaric hypoxia significantly impairs fat oxidation during exercise.
- Maximal fat oxidation rate (MFO) is substantially lower in hypoxia.
- Hypoxia appears to directly influence substrate utilization during exercise, independent of exercise intensity normalization.
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