Teun Remmers

Relationship between PA enjoyment and PA in children | 39 vigorous categories were summed in moderate to vigorous PA (MVPA) (4). In all analyses, PA was conceptualized as the percentage of time spent in the various intensities relative to the total registration time. To be able to capture the intermittent, spontaneous nature of child’s PA, we computed the number of PA bouts. In the present study, a bout of PA consists of at least 1 minute of vigorous PA (i.e. ≥1003 counts per epoch). We used a drop time of 15 seconds, which means that at least three out of four epochs in one minute should be of vigorous PA. Children’s PA is dependent of season (i.e. more PA in spring and summer) (33). Therefore, we computed meteorological seasons at which the PA measurement commenced, and entered these as independent variables in subsequent analyses. We visually inspected the normality assumptions of the percentage active, light, MVPA, and distributions showed to be normal. The number of PA bouts was positively skewed, we therefore we used its natural logarithm for further analyses. Impulsivity Impulsivity is generally defined as a relative inability to plan, control and execute reasoned action (34). For the measurement of impulsivity we used the Impulsivity Scale from the child-reported version (from age 7 onwards) of the Temperament in Middle Childhood Questionnaire (TMCQ) (35,36). This scale is based on the impulsivity dimension of the Child Behavior Questionnaire (CBQ) (37). The CBQ is a larger instrument that assesses temperamental traits of children between three and six years old (37). The impulsivity scale of the TMCQ was previously validated against the CBQ within a sample from the KOALA Birth Cohort study. This validation study supported the applicability of the impulsivity scale as impulsivity was highly related to surgency/extraversion, the higher-order temperamental trait characterized by impulsive and active behavior (36). In the TMCQ, children were asked to respond to 13 statements (e.g. ‘I decide what to do quickly and then go and do it right away’) describing impulsive behaviors and had to choose the answer that applied to them most, using a 5-point Likert scale ranging from 1 (Never) to 5 (Always). Cronbach's alpha for the impulsivity scale in the present sample was 0.69. Corrected-item total correlations ranged from 0.20 to 0.56 for 13 items, indicating sufficient homogeneity of the items (31). Body Mass Index We measured child’s body weight using an electronic scale (CAS personal scale, HE-5) while wearing light sports-clothes, excluding shoes. Height was measured with accuracy of 0.5 centimeters using a telescopic stadiometer (Leicester height measure), without shoes and hair ornaments. Subsequently, we calculated BMI as weight divided by height squared (kg/m 2 ) and we calculated BMI z-scores according to reference values of the fourth Dutch growth study, to standardize for age and gender (38).