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Pediatr."],"abstract":"<jats:sec><jats:title>Background<\/jats:title><jats:p>Increased maximal oxygen uptake (V\u0307O<jats:sub>2max<\/jats:sub>) is beneficial in children with cystic fibrosis (CF) but remains lower compared to healthy peers. Intrinsic metabolic deficiencies within skeletal muscle (muscle \u201cquality\u201d) and skeletal muscle size (muscle \u201cquantity\u201d) are both proposed as potential causes for the lower V\u0307O<jats:sub>2max<\/jats:sub>, although exact mechanisms remain unknown. This study utilises gold-standard methodologies to control for the residual effects of muscle size from V\u0307O<jats:sub>2max<\/jats:sub> to address this \u201cquality\u201d vs. \u201cquantity\u201d debate.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>Fourteen children (7 CF vs. 7 age- and sex-matched controls) were recruited. Parameters of muscle size \u2013 muscle cross-sectional area (mCSA) and thigh muscle volume (TMV) were derived from magnetic resonance imaging, and V\u0307O<jats:sub>2max<\/jats:sub> obtained via cardiopulmonary exercise testing. Allometric scaling removed residual effects of muscle size, and independent samples <jats:italic>t<\/jats:italic>-tests and effect sizes (ES) identified differences between groups in V\u0307O<jats:sub>2max<\/jats:sub>, once mCSA and TMV were controlled for.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>V\u0307O<jats:sub>2max<\/jats:sub> was shown to be lower in the CF group, relative to controls, with large ES being identified when allometrically scaled to mCSA (ES\u2009=\u20091.76) and TMV (ES\u2009=\u20090.92). Reduced peak work rate was also identified in the CF group when allometrically controlled for mCSA (ES\u2009=\u20091.18) and TMV (ES\u2009=\u20090.45).<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusions<\/jats:title><jats:p>A lower V\u0307O<jats:sub>2max<\/jats:sub> was still observed in children with CF after allometrically scaling for muscle size, suggesting reduced muscle \u201cquality\u201d in CF (as muscle \u201cquantity\u201d is fully controlled for). This observation likely reflects intrinsic metabolic defects within CF skeletal muscle.<\/jats:p><\/jats:sec>","DOI":"10.3389\/fped.2023.1211547","type":"journal-article","created":{"date-parts":[[2023,6,14]],"date-time":"2023-06-14T04:51:55Z","timestamp":1686718315000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":5,"title":["Skeletal muscle contributions to reduced fitness in cystic fibrosis youth"],"prefix":"10.3389","volume":"11","author":[{"given":"Owen William","family":"Tomlinson","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alan 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