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.