Longitudinal effects of biopsychosocial variables on physical activity after menarche

The aim of the current study is to analyze the longitudinal effects of certain biopsychosocial variables (socioeconomic status, Body Mass Index (BMI), body image and well-being (QL)), measured at three different menarche stages (S1: before menarche, S2: soon after menarche, and S3: one year after S2), on physical activity and inactivity levels in early adolescence.

The sample comprised 136 Brazilian teenagers (10-13 years old), showing BMI 18.98 kg/m² at the initial assessment, who voluntarily participated in the study. Data concerning the following variables were collected in 2010 (S1), 2011 (S2) and 2012 (S3): family income (FI) (socioeconomic anamnesis), BMI (body mass and height), well-being (Autoquestionnaire Qualité de Vie Enfant Imagé) and body image (Body Shape Questionnaire). The physical activity and inactivity levels were measured in S3, only, through the International Physical Activity Questionnaire. The Pearson's correlation and the longitudinal path analysis technique were used to statistically analyze the data.

The main results indicated that only family income and BMI, measured soon after menarche (S2), showed significant effect on physical activity and inactivity levels. More specifically, family income has positively influenced (β=0.25) physical inactivity levels and negatively influenced (β=-0.14) moderate physical activity levels, whereas BMI has positively influenced (β=0.15) walking levels and negatively influenced (β=-0.13) vigorous physical activity levels.

These results suggest that the body image and well-being perceived by the teenagers at different menarche stages are not determining factors of their physical activity levels in early adolescence. On the other hand, the effects of socioeconomic status and BMI on early adolescent girls' physical activity and inactivity levels depend on the assessment period.