March 2010

Document Type


Degree Name



Dept. of Public Health and Preventive Medicine


Oregon Health & Science University


Background: Childhood and adolescent obesity is an increasingly significant problem in the United States. Inadequate physical activity is hypothesized to be a major contributing factor to this epidemic; however, the evidence linking physical activity patterns and obesity in youth is inconsistent. By using pedometers to objectively measure physical activity, the Social Influences on Adolescent Physical Activity (ADOLPA) study conducted by Oregon Research Institute from 1999-2007 provides a unique opportunity to more accurately characterize the association between physical activity and obesity. Objective: To examine whether meeting recommended physical activity standards of 60 minutes per day of moderate to vigorous activity as measured by pedometer is associated with overweight status in adolescents aged 10-14 years. Design and Methods: A cross sectional analysis was conducted using baseline data from the ADOLPA Study (). All study subjects wore a pedometer for a week, reporting daily number of steps to objectively measure physical activity, in addition to answering an extensive survey. Physical activity levels were defined as Low: less than 10,000 steps per day, Moderate: 10,000 to 12,000 steps per day for girls, 10,000-13,000 steps per day for boys, or High: at least 12,000 steps per day for girls or 13,000 steps per day for boys. The main outcome variable was body mass index (BMI)-for-age percentile divided into two categories: normal weight (<85th percentile) and overweight (including obese)(≥ 85th percentile). Prevalence of adolescents meeting physical activity levels and prevalence of overweight and obesity were determined. Correlations between pedometer recording and self-report measures of physical activity were assessed. The association between physical activity and overweight was assessed using multivariate logistic regression to control for potential confounders. Results: The participants include a total of 371 adolescents aged 10-14 years, 24% of whom were from minority backgrounds. Overall, 44.7 % of the sample was classified as overweight with a BMI-for-age at the 85th percentile or higher, and 23.0% were classified as obese with BMI-for-age at the 95th percentile or higher. There were no significant differences in weight status by age or sex. 26.9 % of the sample met the highest level of physical activity. Girls were significantly more likely than boys to only achieve the lowest level of activity (61% vs. 41%). Three survey questions on physical activity were only weakly correlated with pedometer recordings (r=0.24). Adolescents reporting more or much more exercise than their peers were less likely to be overweight (OR 0.62, 95% CI (0.45, 0.85), p=0.003). The risk of overweight was highest among adolescents in the lowest physical activity level (53.7%) compared with those in the moderate level (41.8%) and the highest level (29.6%). After adjusting for television viewing, household income and sex, the odds ratios (OR, 95% CI) for overweight were 0.64 (0.37, 1.11) for those in the moderate physical activity level (p=0.12), and 0.38 (0.22, 0.66) for those in the highest activity level (p< 0.001). Television viewing was also associated with overweight status, with adjusted odds ratios of 1.7 (1.02, 2.9) for adolescents watching 2-3 hours a day (p = 0.043), and OR of 2.2 (1.01, 3.2) for those watching 4 or more hours a day compared to those watching less than 2 hours a day (p=0.048). Adolescents in households earning more than the median income of $50,000 per year had lower odds of overweight with OR of 0.64 (0.42, 0.99) (p=0.045). Conclusions: Inadequate physical activity, television viewing, and lower socioeconomic status are associated with an increased risk of overweight and obesity for adolescents. Studies evaluating prevention strategies targetting physical activity and sedentary behavior are needed to reduce the prevalence of overweight and obesity among adolecents.




School of Medicine



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