Cardiorespiratory Fitness as a Mediator of the Association between Physical Activity and Overweight and Obesity in Adolescent Girls

Background: Overweight and obesity (OW/OB) continue to be prominent health issues among adolescent girls. However, little is known about the interrelationships between physical activity (PA), cardiorespiratory fitness (CRF), and OW/OB in this population. The objective of this study was to examine whether CRF mediates the relationship between PA and OW/OB in adolescent girls. Methods: Moderate-to-vigorous PA (MVPA), CRF, BMI, and percentage body fat (% BF) were measured in adolescent girls (N = 1519), aged 10-14 years, from 24 urban middle schools located in the Midwestern United States. Structural equation modeling was used to determine whether CRF is a mediator of the association between MVPA and OW/OB (measured as both BMI and % BF). Multigroup analyses were used to determine whether race, puberty, or socioeconomic status moderate the mediation models. Results: The indirect effect of MVPA through CRF on OW/OB was significant for both BMI (p < 0.01) and % BF (p < 0.01), indicating that CRF is a complete mediator between MVPA and OW/OB. Both race and puberty significantly (p < 0.05) moderated the mediation between MVPA and OW/OB. Conclusions: This study demonstrates that CRF is improved by increasing MVPA, and the improvement in CRF results in lower BMI and % BF among adolescent girls.