Miller, Jonathan2017-10-092017-10-092017-07https://hdl.handle.net/11299/190523University of Minnesota Ph.D. dissertation. July 2017. Major: Epidemiology. Advisor: Mark Pereira. 1 computer file (PDF); ix, 207 pages.Interventions to increase population physical activity are often conducted in diverse populations, particularly in schools. Understanding differences in intervention effects and determinants of physical activity across population subgroups should help improve the effectiveness of interventions. We examined how an intervention effect and determinants of physical activity differ by or are consistent across ethnicities/races and the sexes. In the first manuscript, we estimated the effect of the Minne-Loppet Ski Program, an elementary school cross-country ski intervention, on motivation to exercise and tested whether effects differ by ethnicities/race or sex. Motivation to ski increased among Minne-Loppet Ski program participants compared to students in control classrooms. Motivation to exercise increased among African American and white participants but not Hispanic participants. In the second manuscript, we used cross-sectional data from Project EAT-2010 to test a social-ecological model of determinants of physical activity. Determinants clustered into eight factors. A factor that included personal and social determinants had the strongest association with physical activity. In the third manuscript, we used cross-sectional data from Project EAT-2010 to estimate differences in personal, social and environmental determinants of physical activity across ethnicities/races and the sexes in middle and high school students. Most determinants of physical activity did not vary by ethnicity/race. Among females, neighborhood road connectivity, distance to trails and perceived mother’s physical activity differed in their associations with physical activity by ethnicity/race. Among males home media equipment and sports participation differed in their associations with physical activity by ethnicity/race. In the fourth manuscript we used longitudinal data from Project EAT-I through EAT-IV to estimate differences in trajectories of physical activity and its determinants across ethnicities/races and the sexes in middle and high school students. Declines in physical activity happened later among males than among females. Only the association of BMI with physical activity differed by ethnicity/race and sex. The results from these analyses show that there is a great deal of consistency in the determinants of physical activity across ethnicities/races, but differences that emerge should be considered when implementing future physical activity interventions.enAdolescentsChildrenDeterminantsEthnicity/RacePhysical ActivitySex/GenderThesis or Dissertation