Background: Recent increases in the prevalence of adolescent obesity have been widely documented. Whilst there is a common lay perception that the current generation of adolescents is less active than ever before, there is little published data to support this notion. In addition, there is little published data on trends in physical activity in adolescents according to factors such as gender, age and race.
Methods: Data from the US Youth Risk Behavior Survey were used to explore time trends in physical activity (vigorous activity on three or more days in the last week) and inactivity (no vigorous activity in the last week) overall and according to gender, school grade and race amongst US adolescents between 1991 and 2003. Logistic regression was used to assess: the overall change in odds of adolescents being active or inactive per year, the change in odds of adolescents being active or inactive in each survey year compared to the first year for which data was included (1993), and the change in odds of adolescents being active or inactive in each survey year compared to the previous survey year. After analysing data for all individuals combined, separate analyses were performed by gender, school grade and race.
Results: There was evidence of small, but statistically significant, overall trends towards decreased physical activity and increased inactivity over time amongst boys and those in school grades 9 and 10. Whilst few consistent survey to survey trends were seen, there was a significant decrease in the odds of all adolescents, boys and those in school grades 9 and 10 being active between 1993 and 2003 and a significant increase in the odds of the same groups being inactive between 1993 and 2003.
Conclusion: Overall changes in both activity and inactivity were generally small and are unlikely to play a significant role in reported secular trends in overweight and obesity in adolescents.