Oxygen uptake efficiency slope in 8- to 12-year-old boys and girls.

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Oxygen uptake efficiency slope (OUES) is an objective physiological measure that can be obtained from a standard graded exercise test. However, there is conflicting evidence regarding sex differences in OUES values in children. Therefore, this study investigated potential sex differences in absolute, ratio-scaled, and allometrically scaled OUES in 8.0- to 12.0-year-old children. Retrospective and prospective data of 18 boys and 22 girls were utilized. All participants had undergone familiarization before performing a maximal cycle ergometer test to determine OUES. These values were also ratio-scaled and allometrically scaled to mass and body surface area (BSA). Group differences were tested via independent sample t-tests (or Mann-Whitney U if not normally distributed). Absolute OUES values (VO<inf>2</inf> mL∙min-1/log<inf>10</inf>VE L∙min-1) were significantly higher in boys compared to girls (1860.8±359.3 vs. 1514.3±212.6). When scaled to mass (VO<inf>2</inf> mL∙kg-1∙min-1/log<inf>10</inf>VE L∙kg-1∙min-1), OUES was no longer significantly different between groups, but when scaled to BSA (VO<inf>2</inf> mL∙m-2∙min-1/log<inf>10</inf>VE L∙m-2∙min-1), OUES was significantly higher in the boys than the girls (1414.4±204.2 vs. 1268.9±134.6). When allometry was applied for mass (OUES/mass0.444) boys had significantly higher value than girls (350.8±46.7 vs. 305.0±31.5). The present study demonstrated that boys had greater OUES values scaled to BSA and allometrically scaled to body mass. These findings provide further evidence of sex differences with OUES values in preadolescent children and implies the need for sex-specific reference values prior to using OUES for the assessment of cardiorespiratory pathology in children.