Mediating role of physical activity levels on physical fitness in overweight and obese children when Body Mass Index is not a determining factor

Physical fitness is a crucial health indicator in children and adolescents. Despite the global rise in overweight and obesity, the impact of Body Mass Index (BMI) on physical fitness remains unclear. This cross-sectional study aims to investigate: (R1) the differences in physical fitness components and physical activity levels among children according to gender and BMI, and (R2) the mediating role of physical activity in the relationship between BMI and physical fitness components. Material and Methods The sample was made of 180 students aged 11-14 years (n=90 – male; n=90 - female) divided according to BMI cutoff in normal weight, overweight and obese. Physical fitness components were assessed with several tests: Standing Long Jump (SLJ), Medicine Ball Throw 2Kg (MBT), Shuttle Run 10x5m (10x5), and One Mile Walk Test. Physical activity levels were evaluated with a self-reported questionnaire. A two-way factorial MANOVA was conducted to assess the effects of gender and BMI on physical fitness. Additionally, a mediation analysis was performed to explore the effect of physical activity on the relationship between BMI and physical fitness. Results Results revealed significant differences in the Standing Long Jump (SLJ), 10x5 Shuttle Run, One Mile Walk Test, and physical activity levels, with moderate to large effect sizes observed. Males demonstrated higher levels of physical fitness and physical activity levels (PAL) compared to females. Individuals of normal weight were generally more active and stronger than their overweight and obese peers. Mediation analysis revealed that physical activity completely mediates the relationship between BMI and physical fitness components. Conclusions Results from the present study suggest that the development of physical fitness is not solely determined by BMI, but also depends on the daily practice of physical activity. Future research is needed to assess the effect of physical activity in mediating and moderating the relationship between obesity and physical fitness