Adolescent BMI trajectories with clusters of physical activity and sedentary behaviour: an exploratory analysis.

OBJECTIVE: The purpose of this study is to identify distinct body mass index (BMI) trajectories associated with weight classification, and to examine demographic characteristics and clusters of obesogenic behaviours in adolescents with these trajectories.

METHODS: Data were extracted from the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development (n = 1,006, Grades 5-8). The independent variables were physical activity (accelerometer and child report), sports participation, television/video watching time and recreational computer use. The dependent variable was raw BMI. Growth mixture modelling, mixture modelling and independent t-test analyses were used.

RESULTS: Two distinct BMI trajectories were identified - one with the mean BMI within the Overweight-Obese classification (≥85(th) percentile) and the other within the healthy weight classification (5(th)- 84(th) percentile). Two clusters of physical and sedentary behaviours were identified in adolescents with the Overweight-Obese BMI trajectory. These clusters differed in the type of sedentary behaviour (computer vs. television/video). Three clusters were identified in adolescents with the Healthy Weight BMI trajectory. These clusters differed in levels of physical activity and types of sedentary behaviour.

CONCLUSION: This study contributes to the understanding of multi-dimensional obesogenic behavioural patterns and highlights the importance of understanding types of sedentary behaviour in adolescents.