Six-Minute Walk Performance, BMI and Estimated Cardiorespiratory Fitness Among Primary-School Boys: A Large-Scale Regional Study in Southern Italy

Background: This study examined whether measured walking performance, body mass index (BMI) and estimated cardiorespiratory fitness (CRF) differ across the six provinces of Apulia (southern Italy), and whether physical fitness components and psychological variables (perceived self-efficacy [PSE] and enjoyment) are associated with these outcomes in primary-school boys. Methods: A cross-sectional study was conducted among 2700 boys. BMI, Standing Long Jump (SLJ), 4 × 10 m Shuttle Run (4 × 10 m SR), 6-Minute Walk Test and questionnaire data were collected, and VO2max was estimated with the Jalili equation, which combines 6-min walk distance (6MWD) and BMI and was developed in older boys without validation in children aged 8–10 years. Measured 6MWD was analyzed as the primary outcome and estimated VO2max as a complementary outcome, using linear models. Results: Measured 6MWD, SLJ, 4 × 10 m SR did not differ across provinces (all p > 0.50). Province was not associated with 6MWD (p = 0.331), which was positively associated with SLJ and inversely associated with 4 × 10 m SR (both p < 0.001). Estimated VO2max differed across provinces (p < 0.001), but this difference disappeared after accounting for BMI (p = 0.340) and was almost entirely attributable to the BMI term of the estimation equation. No clear independent association emerged for PSE and enjoyment (p = 0.119; p = 0.281). Conclusions: Provincial differences in equation-derived VO2max were almost entirely attributable to differences in BMI, entered through the estimation equation, and should not be interpreted as differences in aerobic capacity. Because the equation was developed in older boys and has not been validated in children aged 8–10 years, these values are indirect, group-level estimates rather than measurements of CRF.