Ability of preschoolers to achieve maximal exercise and its correlation with oxygen uptake efficiency slope ∼ an observational study by direct cardiopulmonary exercise testing

The oxygen uptake efficiency slope (OUES) is a well-established substitute for maximum oxygen uptake ([Image: see text] O(2) max) in submaximal exercise effort among adolescents and adults. Few studies have analyzed the exercise capacity (EC) and OUES of children aged 4 to 6 (preschoolers). Body fat has been proved to negatively affect EC among schoolchildren. The purposes of this study were to assess the capacity of preschoolers in achieving [Image: see text] O(2) max and evaluate the correlation of peak metabolic equivalent (peak MET) and peak oxygen consumption (peak O(2)) with OUES. We also evaluated if body fat affected EC among preschoolers. Forty-three preschoolers under the ramped Bruce protocol of treadmill exercise testing had been retrospectively studied. The criteria for achieving [Image: see text] O(2) max included respiratory exchange ratio (RER) >1.1, heart rate (HR) >85% of age-predicted maximum, and HR >200 bpm. OUES was calculated by the 75% (OUES-75) and the entire (OUES-100) duration of the testing and normalized by body surface area. Body fat was measured using vector bioelectrical impedance analysis. The fat mass (FM) index and fat-free mass index (FFMI) were defined as FM or FFM (kg) divided by height squared (m(2)), respectively. The mean age of the participants was 5.70 ± 0.56. Seventy-nine percent of preschoolers met at least 1 criterion, 36.84% met 2 criteria, and none met all 3 criteria for [Image: see text] O(2). OUES-75 was moderately positively correlated with peak MET (P = .034; Spearman's rho = 0.324) and peak O(2) (P <.001; Spearman's rho = 0.667). OUES-100 was moderately to highly positively correlated with peak MET (P <.001; Spearman's rho = 0.592) and peak O(2) (P <.001; Spearman's rho = 0.825). There were moderate to high positive correlations between FFMI and peak O(2) (P <.001; Spearman's rho = 0.668), OUES-75 (P <.001; Spearman's rho = 0.642), and OUES-100 (P < .001; Spearman's rho = 0.670). None of the preschoolers reached all 3 criteria for [Image: see text] O(2)max. OUES-75 and OUES-100 might be indicators of peak O(2) at submaximal effort. Preschoolers with higher FFMI had better EC during treadmill exercise testing.