Purpose - To determine the annual rate at which physical activity changes in girls during middle school using both objective and self-report measures of physical activity.
Methods - Participants were 6th and 8th grade girls from the control schools in the Trial of Activity for Adolescent Girls (TAAG). Random cross-sectional samples initially were drawn from 6th grade girls (n=786) and two years later from 8th grade girls (n=1545). A cohort of 501 girls was in both the 6th and 8th grade samples. The girls wore an accelerometer for six days and completed the 3-Day Physical Activity Recall (3DPAR). Data were summarized using 3.0-4.6- and 6.5-MET cutpoints for accelerometry and self-reported physical activity. Analyses were performed using repeated measures ANOVA in PROC MIXED.
Results - More than 40% of the girls were White, approximately 20% were African-American, and 20% were Hispanic. The annual percent decrease in physical activity in the cross-sectional sample was approximately 4% (-1.76 min MVPA/day), using accelerometer data. The percent decrease in physical activity based on self-report data was higher, 6-13%, depending on the physical activity variable. Declines tended to be larger in African-American girls, but the ethnic differences were not statistically significant.
Conclusions - Based on comparisons of cross-sectional samples of 6th and 8th grade girls, objectively-measured physical activity declined at a rate of 4% per year
