Correlates of Seasonal Outdoor Physical Activity Measured Using Accelerometers and GPS

Introduction Combining GPS and accelerometer data offers a new opportunity to objectively measure children’s time spent active outdoors [1]. This is important as greater time spent outdoors is related to reduced risk of obesity. We know little about what factors determine children’s outdoor activity. This study uniquely investigated the personal, social and environmental factors associated with objectively measured activity outdoors in children.

Methods Data were collected in the PEACH project, a longitudinal study of 1300 children measured in their final year of primary school and one year later in the first year of secondary school. Children wore an accelerometer (Actigraph GT1M) for 7 days and a GPS (Garmin Foretrex 201) for 3 days after school. Both instruments recorded at 10 second intervals and data were matched based upon the accelerometer time stamp to provide a measure of activity time outdoors [1]. A computerised questionnaire measured self-reported physical environmental (accessibility, aesthetics, safety, constraint, play space, accessibility), social environmental (social norm, independent mobility, parental and peer support) and personal (enjoyment, efficacy, constraint, gender, pubertal status) factors. Neighbourhood deprivation and body mass index (BMI) were also assessed. Multivariable linear regression analyses were carried out using STATA v10 to investigate the association between correlates and outdoor physical activity between 3.30 and 8.30pm after adjusting for clustering within schools. Due to seasonal differences in time spent outside analyses were carried out separately by season.

Results One thousand and ten children (10.95 ± 0.41 years) provided data for analyses. Greater summer time outdoor physical activity was significantly (p<0.05) associated with higher independent mobility (β 99.44, CI:45.11 to 153.77), enjoyment (β 103.61, CI:12.98 to 194.24), desire to ‘get outside’ (β 58.41, CI:11.39 to 105.44) and being male (β -73.02, CI:-140.37 to -5.66). Correlates in winter time included more positive perceptions of traffic safety (β 78.06, CI:17.87 to 138.25), accessibility (β 85.41, CI:29.52 to 141.30) and parental support (β 65.60, CI:5.09 to 126.01). BMI Standard deviation score was inversely related to active time outdoors in both winter (β -27, CI:-53.56 to-0.76) and summer (β -45.82, CI:-72.40 to 19.25).

Discussion and Conclusion This study has highlighted how GPS and Accelerometer data can be combined to capture an important physical activity context – outdoor activity after school. Findings suggest that when environmental constraints are reduced in summer, personal factors may be more salient but in winter a favourable physical and social environment may be crucial for maintaining levels of outdoor physical activity.

References [1] Cooper AR, Page AS, Wheeler BW, Hillsdon M, Griew P, Jago R. Patterns of GPS measured time outdoors after school and objective physical activity in English children: the PEACH project. IJBNPA, 2010;7:31.