Background: Responding to the growing interest in the environmental influences on physical activity, and the concerns about the limitations of self-report data, this study evaluates Global Positioning System (GPS) units for measuring outdoor physical activity.
Methods: Four GPS models were selected to test their accuracy related to adherence to an actual route walked, variations based on position of unit on user's body, and variations against a known geodetic point. A qualitative assessment was performed using the following criteria: a) battery life, b) memory capacity, c) initial satellite signal acquisition time, d) ease of data transfer to other programs, e) wearability, f) ease of operation, g) suitability for specific study populations, and h) price.
Results and conclusions: The Garmin Forerunner provided the most accurate data for data points collected along a known route. Comparisons based on different body placement of units showed some variations. GlobalSat reported battery life of 24 hours, compared with 9-15 hours for the other units. The static test using ANOVA showed that the Garmin Foretrex's data points compared with a geodetic point was significantly more accurate than the other 3 models. GPS units appear promising as a tool to capture objective data on outdoor physical activities.