Portable global positioning units to complement accelerometry-based physical activity monitors.
ABSTRACT This study examines the usefulness of complementing accelerometry-based physical activity measurement with spatial data from portable global positioning system (GPS) units to determine where physical activity occurs.
First, using the geographic distribution of data points and Bland-Altman plots, we examined GPS units' validity and interunit reliability by measuring the distance to a geodetic point. We also assessed interunit reliability by comparing GPS data collected in three built environment contexts. Second, we conducted a pilot study in which 35 participants wore GPS units and accelerometers in free-living conditions for 3 d. Moderate and vigorous physical activity (MVPA) bouts were matched to GPS data. We classified each bout as occurring inside or outside the participant's home neighborhood. Using unpaired t-tests and Fisher's exact tests, we compared neighborhood attributes for participants having the majority of MVPA bouts within their home neighborhood, relative to those with most bouts away from their home neighborhood.
Average distance from each unit to the geodetic point was 3.02 m (SD 2.51). Average bias among units using Bland-Altman plots was 0.90 m, ranging from -0.22 to 1.86 m, within the limits of agreement. For interunit reliability in the built environment contexts, the mean distance difference among units ranged between 10.7 m (SD 11.9) and 20.1 m (SD 21.8). For the pilot study involving participants, GPS data were available for 59.3% of all bouts (67% of MVPA time), of which 46% were in the participants' neighborhood. Participants obtaining most of their MVPA in their neighborhoods tend to live in areas with higher population density, housing unit density, street connectivity, and more public parks.
Data recorded by portable GPS units is sufficiently precise to track participants' movements. Successful matching of activity monitor and locational data suggests GPS is a promising tool for complementing accelerometry-based physical activity measures. Our pilot analysis shows evidence that the relationship between environment and activity can be clarified by examining where physical activity occurs.
SourceAvailable from: Jens Troelsen
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ABSTRACT: Previous behavioural research involving walking has mainly focused on the personal and social factors that can affect physical activity. More recently, studies have been increasing which argue that the built environment has also strong impacts on personal physical activity level, although there is a poor understanding between urban form and physical activity association in children. Nowadays children enjoy less freedom in the urban setting than previously, and it is becoming clear that less independence and mobility constrain children's development. A decline of children's physical activity level is also apparent, which parallels the increase of overweight / obesity and sedentary activities. Thus, there is an urgent need to understand better children's movement patterns as users of the built environment. In these studies, traditional methodologies (e.g. observation, self-reported, questionnaire and so on) are difficult to use in accurately investigating children's outdoor movement. However state-of-art portable Global Positioning System (GPS) technology has made studies of children's outdoor movement possible. In our study, nearly 160 children from 2 local primary schools in the British town of Cheshunt, Hertfordshire have been monitored over a period of four days from September 2005 to June 2006 by fitting children with portable GPS Units and energy monitors. In this paper, 3D geovisualisation is shown to be a very effective tool to display the local travel that children make on foot, the places children go to, and the places where children are most physically active. Children's daily movement pathways are then characterized using a variety of measures, such as gender, age, energy expense, land use location, turning angles, travelling speed and so on. The results shown in this paper indicate how children interact differently with their local environment when they are with adults and or other children and compare these to activity when they play alone. In this way, the level of energy expended under different circumstances can be visualised.