2020, Vol. 7, Issue 6, Part D

Methods: Data from youths 12 to 15 years of age participating in the 2012 NHANES National Youth Fitness Survey (NNYFS) were used. Variables included self-reported moderate-to-vigorous PA (MVPA, min/day), WC (cm), and CRF (ml/kg/min). Linear regression was used to examine the sex-specific influence that MVPA and WC have on CRF while controlling for confounding variables. The multivariate delta method was used to estimate standard errors for the indirect effects.

Results: Findings from the fully adjusted sex-specific models showed MVPA and WC independently and significantly (all p < .05) related to CRF. Mediation analysis for boys indicated a significant indirect effect (ab = 0.0009, 95% CI: 0.0004-0.0015, 29% mediation) of MVPA on CRF through WC. Conversely, MVPA had no significant (p = .277) indirect effect on CRF through WC in girls.

Conclusion: This study shows that WC partially mediates the relationship between PA and CRF in adolescent boys but not girls. These findings highlight that PA can be promoted to improve WC which can then improve CRF in adolescent boys.