The initial sample of 827 (unweighted) participants met inclusionary criteria; however, 38 participants were excluded due to missing data. The final sample included in the analyses was 789 adolescents. Average age was 14.4 years and 48.6% were female. lists frequencies, percentages and standard errors for gender and race/ethnicity. also lists the means and standard errors for age, poverty-to-income ratio, dietary energy intake, anthropometrics, active commuting, and MVPA. Average time spent in active commuting for the entire sample was 8.5 minutes/day (including those who did not travel to school by active commuting in the past 30 days); if we excluded adolescents who did not use active commuting in the past 30 days, average time in active commuting was 18.4 minutes/day.
Comparing demographic characteristics of participants who were included (n = 789) versus excluded (n = 38) from analyses yielded a significant difference in age (P = .016). Excluded participants were older (15.3 ± 0.3 years) than included participants.
Controlling for age, gender, race/ethnicity, poverty-to-income ratio, and energy intake (), active commuting was inversely associated with BMI z-score (std. beta = −0.07, P = .046, partial R2 = .004; total model R2 = .05) and skinfolds (std. beta = −0.06, P = .029, partial R2 = .004; total model R2 = .12). Active commuting was inversely associated with waist circumference, although this association did not reach statistical significance (std. beta −0.06, P = .093, partial R2 = .003; total model R2 = .08). Active commuting was positively associated with average daily MVPA (std. beta = 0.12, P = .024, partial R2 = .02; total model R2 = .31) and before- and after-school MVPA (std. beta = 0.20, P < .001, partial R2 = .06; total model R2 = .20). No significant interactions were found by age group or gender effects on any adiposity outcomes (results not presented).
Standardized Coefficients (Std Beta) for Active Commuting to School’s (ACS) Relationship to Adiposity (Regressions Series 1) or Moderate-to-Vigorous Physical Activity (MVPA; Regression Series 2)
For the mediation analysis ( and ), before- and after-school MVPA significantly mediated the relationship between active commuting and waist circumference (Sobel z = −1.98, P = .048). Before- and after-school MVPA had nonsignificant but borderline mediation of active commuting and BMI z-score (Sobel z = −1.68, P = .093) and skinfolds (Sobel z = −1.81, P = .070). Average daily minutes of MVPA mediated no relationships (P > .1).
Standardized Coefficients* (Std Beta) for Active Commuting to School’s (ACS) Relationship to Adiposity, Controlling for Moderate-to-Vigorous Physical Activity.
Stratification analyses did not yield any significant mediated relationships, thus, indicating that gender and age group did not differently influence or moderate any potential mediation of MVPA to the relationship between active commuting and adiposity.
Because active commuting might also be related to light physical activity (the lower cutpoint defined as ≥ 101 counts per minute35
), we conducted parallel analyses to include the sum of light-, moderate-, and vigorous-physical activity (LMVPA). No significant association was found between active commuting to school (ACS) and LMVPA (P
= .603 for total daily LMVPA or P
= .169 for before- and after-school LMVPA), controlling for covariates. Similarly, LMVPA did not mediate the relationship between ACS and BMI z-score, waist circumference, or skinfolds (all P