A Cluster Analysis of Physical Activity Patterns in Middle School Girls

Cluster analysis is a statistical technique applied to data to identify groups that exhibit similar patterns. However, few studies have used it to examine physical activity (PA) and sedentary behavior in youth. PURPOSE: To identify clusters of 6th grade girls with similar patterns of PA participation and sedentary behaviors, and to determine which patterns are associated with change in PA behavior from 6th to 8th grade. METHODS: The Trial of Activity for Adolescent Girls (TAAG) was a multi-center group-randomized trial designed to test a PA intervention. Data represent a longitudinal examination of a cohort of 957 girls (52% White, 19% African American, 19% Hispanic) from 6th to 8th grade. Clusters were created in 6th grade based on self report of PA and sedentary behavior (3DPAR). Change in participation of moderate-to-vigorous physical activity (MVPA defined as ≥ 3 METS) for 90 min/day objectively measured by accelerometry (ActiGraph 7164) was assessed. Data analysis consisted of FASTCLUS in SAS using mixed model repeated measures analyses. RESULTS: Cluster size ranged from 75 to 253 girls. Girls with the greatest frequency in selected activities were classified into 6 clusters (C1: Educational sedentary (i.e., homework); C2: Sports and play; C3: Organized sports teams/classes in past year; C4: Lifestyle and active travel; C5: Electronic media; C6: Diurnal sleeping). Sixth grade girls in C2, C3 and C4 had the higher percentages for obtaining 90 min/day MVPA (65, 63 and 59%, respectively). There was a significant cluster by time interaction for MVPA (p= 0.08) controlling for age, BMI, race and free/reduced lunch. At the 8th grade follow-up, C3 had the highest percentage of 90 min/day MVPA (47%), but min of MVPA declined among girls in all clusters from 6th to 8th grade (p= 0.001). C2 had the greatest decline in PA participation (-32%) followed by C4 (-24%), while C3 had less of a decline (-16%). CONCLUSION: Sixth grade girls who participate in Sports and play, Organized sports teams/classes or Lifestyle and active travel have higher PA participation, and girls who participate on Organized sports teams/classes have less of a decline in PA behavior in 8th grade. Interventions could be targeted to encourage these activities in girls to promote more participation in MVPA and to blunt the decline in PA observed over time.