Validity and Reliability of an Activity Monitor with the Capability of Providing Geographic Location Using GPS

Purpose To establish the validity and reliability of the GPAC for measuring physical activity and geographic location.

Methods 20 subjects wore both the GRAC and an Actigraph while walking on a treadmill at 3,4, or 5 mph in a randomized order. In addition 24 subjects were asked to wear the GPAC and to record times, places, and activities Typical locations visited were their homes, a classroom building, the outdoor running track, the Mall, a restaurant, etc. Activities included were walking, jogging, driving (car and/or bicycle).

Results The Actigraph had significantly higher activity counts at all speeds than the GPAC (p < 0.001) but there was a significant correlation between the Actigraph and GPAC activity counts (r = 0.976, p < 0.001) Estimates of intrasession reliability for the GPAC ranged from 0.95 to 0MB across the three speeds. Of 120 different way-points visited by the subjects subsequent analysis of the latitude/longitude file enabled the naïve investigator to correctly track 109 of them (91%).

Conclusion The GPAC is a reliable valid tool for measuring physical activity with simultaneous measurement of geographic location.