Long-term trends in physical fitness and body mass among 10- year-olds in Gdansk: findings from a 12-year intervention programme

Introduction
Physical fitness in childhood is a critical determinant of long-term health, influencing the risk of cardiometabolic and emotional disorders in adulthood. The Kasch pulse recovery test (KPRT) is a simple, non-invasive tool for assessing cardiorespiratory fitness (CRF) in population-based studies. This study evaluated the relationship between body mass index (BMI) and physical fitness in 10-year-old children from Gdansk, Poland, over a 12-year period (2011–2023), focusing on sex differences and the impact of the COVID-19 pandemic.

Material and methods
A total of 19,614 children (9,416 girls and 10,198 boys) participating in the health preventive programme were assessed. Body mass index was calculated using anthropometric measurements and categorized as underweight, normal weight, or overweight/obese according to the national centile grids. Physical fitness was evaluated using the KPRT, a 3-minute step test, with heart rate (HR) monitored post- exercise. Data were analysed using χ2 tests and ANOVA (p < 0.05), comparing BMI categories, KPRT scores, and HR across study years and between sexes.

Results
Girls consistently outperformed boys in KPRT scores across all BMI categories (p ≤ 0.05), with a higher proportion of ‘good’ ratings (e.g. 74.9% for girls vs. 61.5% for boys in 2019). Overweight children, especially boys, exhibited significantly poorer KPRT scores (57.1% ‘poor’ ratings in 2023) and higher post-exercise HR (e.g. 139 beats per minute (bpm) for overweight girls vs. 127 bpm for boys in 2023). A positive trend in fitness was observed in the 2015–2019 period, with lower HR (e.g. 114 bpm for girls, 106 bpm for boys in 2017), but fitness declined post-2020, with ‘good’ KPRT ratings dropping to 45.1% (girls) and 32.1% (boys) in 2023, alongside higher HR.

Conclusions
Overweight children, especially boys, are at a greater risk of reduced physical fitness, highlighting the need for targeted interventions. The Kasch pulse recovery test proved effective as a screening tool for assessing CRF in children.