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We then measured indices of mitochondrial respiration capacity, force production, and fatigue resistance in the diaphragm.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>Mitochondrial respiratory capacities (assessed using permeabilized fibres with single or multiple inputs to the electron transport system), citrate synthase activity (a marker of mitochondrial volume), twitch force production, and muscle fatigue resistance increased after exposure to chronic hypoxia in both populations. These changes were not well explained by variation in the fibre\u2010type composition of the muscle. However, there were several differences in diaphragm function in high\u2010altitude mice compared to low\u2010altitude mice. Exposure to a deeper level of hypoxia (9 <jats:styled-content style=\"fixed-case\">kP<\/jats:styled-content>a vs 12 <jats:styled-content style=\"fixed-case\">kP<\/jats:styled-content>a) was needed to elicit increases in mitochondrial respiration rates in highlanders. Chronic hypoxia did not increase the emission of reactive oxygen species from permeabilized fibres in highlanders, in contrast to the pronounced increases that occurred in lowlanders. In general, the diaphragm of high\u2010altitude mice had greater capillary length densities, produced less force in response to stimulation and had shorter relaxation times. The latter was associated with higher activity of sarcoplasmic reticulum Ca<jats:sup>2+<\/jats:sup>\u2010<jats:styled-content style=\"fixed-case\">ATP<\/jats:styled-content>ase (<jats:styled-content style=\"fixed-case\">SERCA<\/jats:styled-content>) activity in the diaphragm of high\u2010altitude mice.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusion<\/jats:title><jats:p>Overall, our work suggests that exposure to chronic hypoxia increases the capacities for mitochondrial respiration, force production and fatigue resistance of the diaphragm. However, many of these effects are opposed by evolved changes in diaphragm function in high\u2010altitude natives, such that highlanders in chronic hypoxia maintain similar diaphragm function to lowlanders in sea level conditions.<\/jats:p><\/jats:sec>","DOI":"10.1111\/apha.13030","type":"journal-article","created":{"date-parts":[[2018,1,10]],"date-time":"2018-01-10T12:51:58Z","timestamp":1515588718000},"source":"Crossref","is-referenced-by-count":48,"title":["Effects of chronic hypoxia on diaphragm function in deer mice native to high altitude"],"prefix":"10.1111","volume":"223","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5389-8692","authenticated-orcid":false,"given":"N. J.","family":"Dawson","sequence":"first","affiliation":[{"name":"Department of Biology McMaster University Hamilton ON Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"S. 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