Teun Remmers

86 | Chapter 6 Abstract Introduction : Understanding how the weather affects physical activity (PA) may help in the design, analysis and interpretation of future studies, especially when investigating PA across diverse meteorological settings and with long follow-up periods. The present longitudinal study first aims to examine the influence of daily weather elements on intra- individual PA patterns among primary school children across four seasons, reflecting day- to-day variation within each season. Second, we investigate whether the influence of weather elements differs by day of the week (weekdays vs. weekends), gender, age, and Body Mass Index. Method : PA data were collected by ActiGraph accelerometers for one week in each of four school terms that reflect each season in southeast Australia. PA data from 307 children (age range 8.7-12.8 years) were matched to daily meteorological variables obtained from the Australian Government’s Bureau of Meteorology (maximum temperature, relative humidity, solar radiation, day length, and rainfall). Daily PA patterns and their association with weather elements were analyzed using multilevel linear mixed models. Results : Temperature was the strongest predictor of moderate- and vigorous PA, followed by solar radiation and humidity. The relation with temperature was curvilinear, showing optimum PA levels at temperatures between 20 and 22 degrees Celsius. Associations between weather elements on PA did not differ by gender, child’s age, or Body Mass Index. Conclusions : This novel study focused on the influence of weather elements on intra- individual PA patterns in children. As weather influences cannot be controlled, knowledge of its impact on individual PA patterns may help in the design of future studies, interpretation of their results, and translation into PA promotion.