Teun Remmers

Relationship between PA and the development of BMI in children | 19 Methods Study design and population The longitudinal relationship between PA and BMI (Figure 1) was examined in two subsequent time periods (diagonal arrows in Figure 1), further defined as the “period”. In the first period (i.e. first diagonal line in Figure 1), we measured a child’s PA level at 4-5 years (T 0 ), and body height and weight at both 4-5 (T 0 ) and 6-7 years (T 1 ). In the second period (i.e. second diagonal line in Figure 1), we measured a child’s PA level at 6-7 years (T 1 ), and body height and weight at both 6-7 (T 1 ) and 8-9 years (T 2 ). All parents gave written informed consent. The present study was approved by the Medical Ethics Committee of Maastricht University Medical Center+. Figure 1: Conceptual model, presenting longitudinal relationships between physical activity (PA) and body composition (BMI). Note: 1 : first period; 2 : second period. The present study is a prospective study, nested in the KOALA Birth Cohort Study. The study started in 2000 with the recruitment of healthy pregnant women from the general population who participated in an ongoing prospective cohort study on pregnancy-related pelvic girdle pain (conventional recruitment group, N = 2343). In addition, healthy pregnant women with an alternative lifestyle were recruited through Steiner schools, organic food shops, and anthroposophic doctors, midwives and magazines (alternative recruitment group, N = 491) (16). The current study was performed in a subsample of the KOALA cohort. Children were eligible for the first assessment period (T 0 ) if all questionnaires in the child’s first two years of age were complete, and if the child resided within 20 kilometers of six selected study locations, an inclusion criterion for a prior study within the KOALA cohort (7). Children were eligible for the second assessment period (T 1 ) if accelerometer data were available from the first period, and if the mother had participated in blood sampling at 36