Neurologic and Metabolic Challenges at High Altitudes

Hypoxia resulting from a drop in the oxygen pressure in the atmosphere with elevation is a hallmark of the high altitude (HA) environment, with cold and requires acclimatization. Despite such environmental challenges, HA is a frequent exposition challenge for travelers, mountaineers, workers, and military personnel. Ambient or exercise-induced, muscle hypoxia triggers complex angio-adaptive responses in the skeletal muscle tissue and capillaries. These are due to the expression of several angio-adaptive molecules: Hypoxia-Inducible Factor (HIF) and Vascular Endothelial Growth Factors (VEGF) a polypeptide leading to the growth, and stabilization of muscle capillaries. A series of biochemical changes and released molecules occur at HA for hypoxia stimulation by HIF on circulation. This remarkable plasticity of the capillary network is referred to as adaptation at the cellular and subcellular levels. Other physiological adaptations occur in the heart, breathing, circulation, and hematopoiesis. Hypoxic stress might also be exploited for potential benefits. Endurance exercise might benefit if first done at HA, increasing hematocrit. This has been exploited in controlling skeletal muscle performance during physical exercise at HA and subsequently at low altitudes. The major skeletal adaptive responses to hypoxia will be discussed, including contraindications and advantages of HA exposition.