Physical Activity Among Teenagers in a Multi-Ethnic Neighborhood in Copenhagen, Denmark – Combining GPS and Accelerometer Data Using PALMS and ArcGIS

Background Large changes in physical activity (PA) can be observed among teenagers. The majority of 11 year olds in Denmark do meet the recommend level of PA; the majority of 15 year olds do not. The chances of not meeting the recommended level of PA as adults are strongly correlated with not meeting them at 15. For that reason, reducing the number of 15 year olds that do not meet the recommended level of PA is of great interest. There are many hypotheses as to what causes these changes, but no consensus has been reached. One hypothesis currently explored in Denmark is that teenagers are more active if they live in an attractive neighborhood with abundant possibilities for them to be physically active, as well as good possibilities to cycle to school. However, relatively little is known about the factors that affect the movement pattern of teenagers. Furthermore, many previous studies in this field have used subjective or self reported measures for PA and/or environment which makes interpreting the validity of the results more difficult. In past few years the first studies have been conducted using accelerometers and GPS, resulting in objective measures for both PA and location. However, most of these studies can be characterizes as pilot studies as they have been cross-sectional and had a relatively small number of participants.

Objectives The overall objective of our project was to conduct an intervention study with a relatively large number of participants, using objective measurements by means of accelerometers and GPS, in order to be able to describe the relation between after school PA and environmental factors for 11-15 year olds. The intervention involved regeneration of a low income neighborhood through building renovation, renewal of green spaces, redesign of streets, and community involvement programs. The specific objective for this paper was the development of suitable methods for compilation and analysis of accelerometer, GPS and GIS data collected for many participants prospectively.

Methods Almost 450 teenagers enrolled at three public schools in Copenhagen, the capital of Denmark, wore an accelerometer (ActiGraph GT3X) and a GPS (Qstarz BT-Q1000X) for 7 days (5 school days, 2 weekend days) to determine their level of activity and movement patterns. Their GPS position was recorded every 15 seconds and their activity level was registered every 2 seconds. The schools were located in relatively poor multi-ethnic neighborhoods and the majority of our respondents had a non- Danish cultural background. Participants also completed surveys assessing their PA behavior and opinions about their neighborhood. All GPS and accelerometer data were compiled and joined using a beta version of PALMS (Physical Activity Location Measurement System), developed by the Center for Wireless & Population Health Systems at the University of California, San Diego. PALMS is web-based system that supports data collection and analysis for exposure biology studies from multiple participants within studies. The outputs PALMS produces basically consist of GPS points linked with PA data for those points. These data point can then be classified in trips, activity bouts and activity levels. All PALMS outputs were imported into ArcGIS, which enabled inclusion of environmental data, and ArcGIS served as platform for further analysis.

Results Our results show that it is feasible to compile and analyze large data sets of combined GPS and accelerometer data using PALMS and ArcGIS. The results reveal the numerous possibilities and great potential of combining large data sets of GPS, accelerometer and GIS data. Our study will be able to monitor changes in temporal and spatial activity patterns over time. From the baseline data we will be able to establish how much time is spent in PA within and outside of the children’s neighborhoods, specific locations that support more intense PA, and environmental and demographic correlates of active commuting to school.

Conclusions The Physical Activity Location Measurement System (PALMS) holds great promise for aiding future studies using accelerometers and GPS. This is the first prospective study of PA temporal and spatial patterns measured by GPS and accelerometer in low income children. The baseline measures from this study already provide interesting comparison of neighborhood effects in a low income ethnically diverse population of adolescents at risk for reductions in PA.

Support This study was supported by the The TrygFonden Centre for Applied Research in Health Promotion and Disease Prevention (www.forebyggelsescenter.dk/?ver=uk).