FIGURE 1.

Contribution of ambient hypoxia and exercise to induce a hypoxic stress in skeletal muscle. A drop in the partial pressure of oxygen (PO₂) in the muscle tissue can result from a decrease in ambient PO₂ (e.g., altitude) as well as an unbalanced between blood supply to the muscle cells and their increase metabolic needs during exercise. In response to muscle hypoxia angio-adaptive responses will take place to maintain an optimal oxygen supply to myofibers and to preserve muscle function. This is of particular relevance in the context of mountaineering activity as well as exercise training strategies using ambient hypoxia for athletes or clinical populations. As discussed in the text, the impact of ambient hypoxia on skeletal muscle PO₂ seems rather modest (+) compared to the impact of exercise in generating a local hypoxic stress (++). The combination of ambient hypoxia exposure and exercise might exacerbate this hypoxic stress (+++).