Physical activity in Swedish and Chinese young children and their parents

Sammanfattning: Physical activity is believed to affect health, already in childhood. Studies of physical activity in children under the age of three are, however, sparse. The overall aim of this thesis was to explore physical activity and its possible correlates in Swedish and Chinese children, aged one and two, at high and low risk for obesity. Physical activity levels and patterns among parents in Sweden and China were also examined. Study I was a calibration study where children, 15 to 36 months old, were recruited from four preschools in Stockholm, Sweden. Physical activity data, measured with accelerometry, was compared against data from Children´s Activity Rating Scale (CARS). Accelerometer count thresholds for sedentary, low- and high-intensity physical activity was derived (n=26) and cross-validated (n=12). Studies II-IV were explorative cross-sectional studies where physical activity levels, patterns and correlates were examined among one- (Study III) and two-year-old children (Studies II and IV), participating in Early STOPP (Stockholm Obesity Prevention Project) Sweden (Studies II and IV) and China (Studies III and IV). Children and their parents wore an accelerometer for seven days to assess average physical activity (counts per minute) and time spent at different intensities. Differences between weekdays and weekend days were examined as were correlations with sex, Studies II-IV were explorative cross-sectional studies where physical activity levels, patterns and correlates were examined among one- (Study III) and two-year-old children (Studies II and IV), participating in Early STOPP (Stockholm Obesity Prevention Project) Sweden (Studies II and IV) and China (Studies III and IV). Children and their parents wore an accelerometer for seven days to assess average physical activity (counts per minute) and time spent at different intensities. Differences between weekdays and weekend days were examined as were correlations with sex, body mass index (BMI), motor skills and family-related factors. The intensity thresholds developed in Study I were found valid for two-year-old children. Swedish two-year-old children had an intermittent activity pattern with short bursts of high intensity physical activity (Study II). At this age, Swedish children accumulated 2989 (SD 702) counts per minute and spent 57%, 34% and 9% of the day respectively in sedentary, at low- and high-intensity. Chinese children accumulated 1997 (SD 899) counts per minutes and spent 70% of the day being sedentary, 25% at low- and 5% at high-intensity (Study IV). Swedish children varied their activity levels more over the day, compared with their Chinese counterparts (Study IV). In both countries, activity levels were similar on weekdays and weekend days. No association was found between physical activity and sex, BMI, motor skills or any family-related factor at age one (Study III) or two, except for a positive association between fathers’ and boys’ physical activity at age two in Sweden (p<0.05, r=0.49 on weekdays and r=0.37 on weekends) (Study IV). Swedish parents were more active than their Chinese counterparts (p<0.05), and mothers were more active than fathers in both countries (p<0.05) (Study IV). In conclusion, physical activity levels and patterns in young children and their parents differ substantially between countries. This indicates that physical activity can be markedly modified by environmental or socio-cultural factors already at two years of age.