The primary muscle used for inspiration is the diaphragm. Emerging data on recent animal model studies have shown that hypoxia contributes to diaphragm adaptation in chronic respiratory disease and high altitude. Interestingly, the diaphragm develops hypoxic tolerance on the cellular level by activation of hypoxic-inducible factor (HIF). Other mechanisms of adaptation include activation of MAP kinases, reduced muscle fiber cross-sectional area, and decreased mitochondrial respiration. However, these changes occur at the expense of the diaphragm’s peak-force generating capacity; this may lead to diaphragm weakness with sustained hypoxic exposure. Reactive oxygen species (ROS) may be both beneficial and detrimental to the adaptation to hypoxia. Antioxidants may help to lessen the adverse effects of hypoxia on the diaphragm’s function. 

http://journal.frontiersin.org/article/10.3389/fphys.2016.00623/abstract