A longitudinal study of the relationships between physical activity, body mass index, and physical self -perceptions in youth

Promoting physical activity and preventing overweight and obesity are important health goals for the nation. The primary purpose of this study was to detennine how physical activity and physical self-perceptions change over 27 months. The secondary purpose was to provide a better understanding of the relationships between physical activity, body mass index, and physical self-perceptions in youth. Complete data was collected on 206 students at baseline (grades 3--6) and 27-month follow-up (grades 5--8). Yamax Digiwalker SW-200 (Tokyo, Japan) and Walk4Life My Life Stepper 2525 pedometers (Plainfield, Illinois, USA) were used to assess physical activity at baseline and follow-up respectively. Height and weight measures were collected to determine body mass index. The Children and Youth version of the Physical Self-Perception Profile (CY-PSPP) was used to assess physical self-perceptions. A mixed design analysis of variance (ANOVA) procedure and mixed design multivariate analysis of variance (MANOVA) procedure were conducted to determine if children's physical activity and physical self-perceptions change over 27 months. For physical activity, the ANOVA revealed a significant time by grade interaction (p < .001, partial &eegr;2 = .10). Post hoc analysis revealed that students in grades 3 and 4 accumulated significantly more daily step counts (1,830--1,963) at follow-up. For physical self-perceptions, the MANOVA revealed a significant time main effect (p < .01, partial &eegr; 2 = .16). Post hoc analysis revealed that children's perceptions of body attractiveness (p < .01) and physical strength ( p < .001) significantly decreased over 27 months. Two separate hierarchical multiple regression analyses were conducted to predict follow-up physical activity and follow-up body mass index. Both overall regression models were statistically significant and explained 31% and 27% of the total variance for follow-up physical activity and follow-up body mass index, respectively. Perceptions of baseline physical condition and body attractiveness were significant contributors to both follow-up physical activity and follow-up body mass index after controlling for demographics and baseline physical activity. The information derived from this study may aid interventionists and practitioners in designing effective programs to promote physical activity and prevent overweight and obesity in youth.