Relationship between age and cardiorespiratory fitness in active youth: evidence from the COR-School project

Abstract

Cardiorespiratory fitness is a key health marker in childhood and adolescence and is associated with lower future cardiovascular and metabolic risk. This study, conducted within the COR-School project, examined the relationship between age and cardiorespiratory fitness in 685 physically active Spanish children and adolescents (420 boys and 265 girls) aged 8–16 years. All participants completed the 20m shuttle run test following a standardised protocol, with total distance covered and age recorded. Analysis revealed a significant positive correlation (r = 0.35; p < 0.001), with each additional year of age associated with an average increase of more than 90 meters covered. Boys outperformed girls across all age groups, although age remained the main predictor of performance. Compared with European reference values from the FitBack project, the COR-School cohort achieved higher results. This suggests that physically active youth participating in organised sports tend to present better cardiorespiratory fitness levels than the reference population. These findings confirm the value of the 20mSRT as a simple, reliable tool for population monitoring, inequality detection, and designing school- and community-based health promotion strategies.