Validation of a VO2max Z-score model for fitness assessment in a healthy Spanish pediatric population

Abstract

Introduction and objectives

Maximal oxygen uptake is the gold standard for assessing aerobic capacity in children and adolescents. Its interpretation requires robust reference models. A pediatric Z-score model has recently been developed, but external validation in independent cohorts is essential to confirm its applicability.

Methods

We conducted a multicenter validation study including a total of 1046 healthy participants (mean age, 12.0  ± 2.6 years), composed of 2 cohorts: a prospective Spanish validation cohort (n  =  175) and a previously published reference cohort (n  =  871). The Z-score model was compared with historical weight- and height-based linear equations in terms of correlation, prediction error, and classification of impaired aerobic fitness. Subgroup analyses were performed by sex and body mass index.

Results

The Z-score model showed the strongest correlation between predicted and observed maximal oxygen uptake (R²  =  0.70), outperforming weight-based (R²  =  0.64) and height-based (R²  =  0.66) equations. It yielded smaller prediction errors among body mass index groups and identified 14% of participants as having impaired aerobic fitness, compared with 20% and 23% using weight- and height-based reference models, respectively. The Z-score model showed improved consistency and reduced bias, particularly in overweight participants.

Conclusions

The pediatric Z-score model demonstrated superior accuracy, consistency, and classification reliability compared with linear equations in a large, independent Spanish cohort. Its adoption may enhance the interpretation of pediatric cardiopulmonary exercise testing, support early identification of reduced aerobic fitness, and guide prevention strategies and tailored interventions.

Registered on ClinicalTrials.gov (NCT04876209).