The oxygen uptake efficiency slope does not accurately predict O_2peak of children - the Arkansas Active Kids study

Cardiorespiratory fitness (CRF) is a vital indicator of health. However, accurately measuring peak oxygen consumption ( $$ O_2peak) to determine CRF in children can be challenging. The oxygen uptake efficiency slope (OUES) has been proposed as an alternative metric for predicting $$ O_2peak in children, but its accuracy and agreement with measured $$ O_2peak remain unclear.

A post hoc analysis was conducted in 94 children (ages 7-10 years) who completed an incremental cycle ergometer test to measure $$ O_2peak. Body composition (Dual-energy X-ray absorptiometry) was measured, and fat mass index (FMI, kg/m²) and fat-free mass index (FFMI, kg/m²) were calculated. OUES was determined using all respiratory data (OUES_100%) collected during the cycle ergometer test and using data only up to 60% of heart rate reserve (OUES_60%HRR). Regression equations to predict $$ O_2peak (Pred- $$ O_2peak) were derived from simple and multiple linear regression analysis. Bland-Altman analysis assessed the level of agreement between Pred- $$ O_2peak and measured $$ O_2peak.

OUES_60%HRR (β = 0.46, p < 0.0001), age (β = 56.0, p = 0.0004), White race (β = 173.3, p < 0.0003), FFMI (β = 0.98.6, p < 0.000), and FMI (β = -0.40.8, p < 0.000) were retained in the final model. The difference between measured $$ O_2peak and Pred- $$ O_2peak was not different from zero (p = 0.999). There was a positive association between the difference of measured $$ O_2peak and Pred- $$ O_2peak and the average of the two methods (β = 0.79, p = 0.0028).

There was no mean bias between measured $$ O_2peak and Pred- $$ O_2peak. However, magnitude bias was present even after considering other significant predictors of $$ O_2peak (FMI, FFMI, race, and age) in the regression equation. Caution is advised when using OUES to predict $$ O_2peak in children.