Moderators in a physical activity intervention for adolescent girls.

Background: The purpose was to explore whether baseline sociodemographic and physical characteristics moderated effects of an intervention on moderate-to-vigorous physical activity (MVPA), percent body fat, body mass index z-score, and cardiorespiratory fitness (CRF) at post intervention, relative to the control condition.

Methods: A secondary analysis of data from a group randomized trial including 24 schools (12 intervention and 12 control; N = 1519 girls) was conducted. Age, ethnicity, race, socioeconomic status, and pubertal stage were assessed via survey. Height, weight, MVPA (min/h), percent body fat, and CRF were measured. Mixed-effects linear models were performed.

Results: Compared to the control, the intervention increased overweight and obese girls' CRF (b = 0.28, p = 0.049; b = 0.31, p < 0.01, respectively), but not healthy weight girls' CRF (b = 0.04, p = 0.706). Pre- to mid-puberty girls in the intervention group had slightly lower post-intervention MVPA than those in the control (3.04 vs. 3.31, p = 0.055), while late to post-puberty intervention and control girls' post-intervention MVPA was similar (3.12 vs. 3.04, p = 0.542).

Conclusions: A PA intervention can improve overweight and obese girls' CRF, possibly attenuating their cardiovascular risk. Effective strategies are needed to assist adolescent girls, especially those in pre- to mid-puberty, in maintaining their MVPA after an intervention ends.

Impact: Moderators of physical activity intervention effects among adolescent girls are important to identify because the effectiveness of these interventions to date in this population has been limited. This article contributes to the notable gap in knowledge regarding moderators in physical activity interventions involving adolescent girls, particularly baseline characteristics that may moderate their responses to physical activity interventions. Awareness of the moderators can be useful for determining the type of intervention that may be successful in subgroups of adolescent girls and for tailoring a physical activity intervention to optimally meet each girl's needs to achieve maximal effects. Findings show that weight status moderated the intervention effects on cardiorespiratory fitness. Compared to the control condition, the intervention increased overweight and obese, but not healthy weight, girls' cardiorespiratory fitness. A physical activity intervention can improve overweight and obese girls' cardiorespiratory fitness, possibly attenuating their cardiovascular risk. Therefore, it is essential to include overweight and obese girls in PA interventions to help them reap this important benefit.