Related Experiment Videos
Human muscle adaptations to chronic hypoxia.
Progress in Clinical and Biological Research
|January 1, 1983
Summary
Maximal aerobic power (V02max) declines at high altitudes due to complex physiological changes. Acclimatization involves both beneficial and detrimental adaptations that interact, explaining the persistent drop in V02max.
Area of Science:
- Exercise Physiology
- Altitude Physiology
- Human Adaptation
Background:
- Maximal aerobic power (V02max) decreases with increasing altitude, a phenomenon observed in both acute and chronic hypoxia.
- The precise physiological mechanisms underlying this persistent reduction in V02max despite acclimatization remain incompletely understood.
Purpose of the Study:
- To investigate the physiological adaptations in skeletal muscle and cardiorespiratory function following prolonged exposure to extreme altitude.
- To elucidate the factors contributing to the lack of improvement in maximal aerobic power after high-altitude mountaineering.
Main Methods:
- Biopsies of the vastus lateralis muscle were analyzed for capillary-to-fiber ratio, fiber diameter, mitochondrial volume, protein concentration, and succinate dehydrogenase (SDH) activity.
- Cardiac output and vastus lateralis blood flow were measured during submaximal exercise.
- Oxygen uptake (V02) on-response kinetics were assessed during submaximal workloads.
Main Results:
- Muscle fiber diameter decreased, while mitochondrial-to-fiber volume ratio increased. Muscle protein concentration and SDH activity were significantly reduced.
- Cardiac output and vastus lateralis blood flow were substantially decreased during submaximal exercise.
- The V02 on-response kinetics were delayed, indicating slower oxygen utilization.
Conclusions:
- The lack of beneficial effects of acclimatization on maximal aerobic power is likely due to an interplay of positive adaptations (e.g., increased hematocrit) and negative changes (e.g., reduced blood flow, muscle mass, and oxidative capacity).
- Hypoxia-induced alterations in muscle structure, reduced cardiovascular function, and impaired oxygen utilization kinetics contribute to the observed decrease in V02max at high altitudes.