Predicting change in physical activity, dietary restraint, and physique anxiety in adolescent girls: examining covariance in physical self-perceptions

OBJECTIVES: To examine: i) the mean changes in adolescent females' body mass index (BMI), global self-esteem, physical self-perceptions, social physique anxiety, physical activity, and dietary restraint; ii) the stability of measuring self-perceptions, BMI, self-esteem, physique anxiety, activity, and dietary restraint; and iii) the relationships among changes in these variables over 12 months. METHODS: 631 female adolescents (15-16 years old) involved in a two-year study of self-report measures completed validated questionnaires in high school classroom settings. RESULTS: There were small but significant group increases in BMI and social physique anxiety and significant decreases in sport, conditioning, and strength physical self-perceptions and physical activity. Stability analysis indicates moderate to strong stability for all variables. Change analyses indicated that BMI, due to its high stability, is a poor predictor of change in all variables. Stronger significant correlations were noted between change in body appearance self-perceptions and change in social physique anxiety (r=-0.54) and dietary restraint (r=-0.27). There was also a significant relationship between change in physical activity and the physical self-perceptions, although conditioning was the only significant (p<0.05) predictor of change in physical activity (beta=0.340). INTERPRETATION: Physical self-perceptions are a stronger predictor of change in physical activity, dietary restraint, and social physique anxiety compared to BMI. This demonstrates the importance of physical self-perceptions when investigating health-related behaviours associated with dieting and physical activity. The decline in physical activity and increase in BMI is an ongoing concern, as is the link between body appearance self-perceptions and dietary restraint and social physique anxiety.