title: Factors associated with changes in physical activity: a cohort study of inactive adolescent girls.
abstract: OBJECTIVE
  To identify factors associated with changes in physical activity in adolescent girls at risk for sedentary lifestyles and obesity.
  
  
  METHODS
  A cohort study was performed with 201 high school girls recruited to participate in an evaluation study of a school-based obesity prevention physical education program. Three assessments were performed during an 8-month period.
  
  
  METHODS
  Associations between physical activity and a range of personal factors (self-acceptance, self-worth, athletic competence, body image, depressive mood, perceived benefits, enjoyment of physical activity, self-efficacy, and body mass index), behavioral factors (watching television and time constraints), and socioenvironmental factors (social support and costs/resources) were assessed.
  
  
  RESULTS
  The 2 strongest and most consistent factors associated with change in physical activity were time constraints and support for physical activity from peers, parents, and teachers. Measures assessing self-perceptions, global (ie, self-worth) and specific to physical activity (ie, self-efficacy to be physically active), were also associated with change in physical activity. For example, a decrease of 2.0 U for an adolescent's perceived time constraints (possible range, 3.0-12.0 U) would be expected to lead to an increase of 53 minutes of moderate to vigorous physical activity per week (95% confidence interval, 33-72 minutes). An increase of 2.0 U in perceived support for physical activity (possible range, 3.0-12.0 U) would be expected to lead to an increase of 35 minutes of moderate to vigorous physical activity per week (95% confidence interval, 13-56 minutes). An increase of 3.0 U on the self-worth scale (possible range, 5.0-20.0 U) might be expected to lead to an increase of 19 minutes of moderate to vigorous physical activity per week (95% confidence interval, 0-40 minutes).
  
  
  CONCLUSIONS
  The effectiveness of interventions aimed at increasing physical activity among adolescent girls might be enhanced by engaging support from friends, family, and caring adults; addressing real and perceived time constraints; and helping adolescent girls feel more confident about themselves and their ability to engage in physical activity.
authors.affiliation: Division of Epidemiology, School of Public Health, University of Minnesota, Minneapolis 55454, USA. Neumark@epi.edu
authors.forename: Dianne
authors.initials: D
authors.lastname: Neumark-Sztainer
authors.forename: Mary
authors.initials: M
authors.lastname: Story
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Hannan
authors.forename: Terri
authors.initials: T
authors.lastname: Tharp
authors.forename: Jeanna
authors.initials: J
authors.lastname: Rex
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior / Q000523:psychology*; D001741:Black or African American / Q000706:statistics & numerical data; D000367:Age Factors; D015992:Body Mass Index; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007899:Leisure Activities; D009043:Motor Activity; D015999:Multivariate Analysis; D009765:Obesity / Q000517:prevention & control / Q000523:psychology; D010806:Physical Education and Training / Q000379:methods; D012649:Self Concept; D012944:Social Support; D011795:Surveys and Questionnaires; D013997:Time Factors