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Kara L. Gavin, Julian Wolfson, Mark Pereira, Nancy Sherwood and Jennifer A. Linde

Background: This analysis helps clarify the individual and joint effects of moderate to vigorous physical activity (MVPA) in concert with significant life events (eg, divorce, marriage, job change or loss, pregnancy, etc) on weight following a behavioral weight loss intervention. Methods: Data from the Tracking Study weight loss trial were utilized to perform a 4-way decomposition of moderation and mediation of life events (≥ 1 vs 0) and MVPA (low <2500 kcal vs high ≥ 2500 kcal) on 24-month weight. Results: The total effect of life events and MVPA on weight was estimated to be 1.63 kg (95% confidence interval = 0.30 to 2.96; P = .02). The controlled direct effect of life events on 24-month weight suggested that experiencing at least one life event controlling for MVPA was associated with an increase of 2.31 kg (95% confidence interval = 0.29 to 4.33) at 24 months. Other interaction and mediation estimates were not statistically significant. Conclusions: This analysis offers new potential for examining health behaviors that may act as both mediators and effect modifiers of health. Although more work is needed to understand the interaction of life events and MVPA on weight loss maintenance, findings help rule out mediation. Life events and MVPA should be considered for their unique effects on weight loss maintenance in the future.

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Jonathan Miller, Mark Pereira, Julian Wolfson, Melissa Laska, Toben Nelson and Dianne Neumark-Sztainer

Background: Interventions to raise population physical activity generally show modest effects; one possible reason is that trends and determinants of moderate to vigorous physical activity (MVPA) differ between population subgroups. This study examined differences in trends and determinants of reported MVPA by ethnicity/race and sex in a 15-year longitudinal study. Methods: Participants (n = 2092) in the Project Eating and Activity in Teens and Young Adults study were surveyed on MVPA behavior and potential determinants from adolescence to young adulthood. Generalized estimating equations were used to model age trends in MVPA and associations with determinants. Results: Mean MVPA declined by 2.1 hours per week over 15 years of follow-up from adolescence to young adulthood. Asian males reported the lowest levels of MVPA at each age. Nonwhite females reported less MVPA than white females at each age. The association of body mass index (BMI) with MVPA differed by sex and ethnicity/race. Asian males and females showed lower levels of MVPA at both low and high BMI. Conclusions: Interventions to increase MVPA may need to begin earlier among Asian men and nonwhite women than among other groups. Asian adolescents with lower BMI show lower MVPA and may benefit from additional intervention efforts compared with Asian adolescents with normal BMI.

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Jonathan M. Miller, Mark A. Pereira, Julian Wolfson, Melissa N. Laska, Toben F. Nelson and Dianne Neumark-Sztainer

Background: This study tested for differences in personal, social, and environmental correlates of moderate to vigorous physical activity (MVPA) across ethnicity/race in male and female adolescents. Methods: Self-reported MVPA and 47 potential correlates of MVPA were measured in an ethnically/racially diverse cross-sectional sample of adolescents, in Minnesota, who participated in EAT-2010 (Eating and Activity in Teens). Interactions of potential correlates with ethnicity/race on MVPA were tested in linear hierarchical regression models in boys and girls. Results: Boys reported 1.7 more weekly hours of MVPA than girls. White adolescents reported 1.1 to 2.1 more weekly hours of MVPA than nonwhite adolescents. Among girls, neighborhood road connectivity was negatively correlated with MVPA among Hispanic and Asian participants. Among boys, sports participation was positively correlated with MVPA among all ethnicities/races, except Asians. Home media equipment was positively correlated with MVPA among Hispanic boys, but negatively correlated among white boys. Conclusions: A few correlates of physical activity among adolescents differed intersectionally by ethnicity/race and sex. Sports participation and home media equipment may have differing impacts on physical activity across ethnicities and races in boys, whereas neighborhood features like road connectivity may have differing impacts on physical activity across ethnicities and races in girls.