A comparative evaluation of three accelerometry-based physical activity monitors

Purpose: Accelerometry-based activity monitors offer promise for the assess ment of free-living physical activity. They provide an objective record of frequency, intensity, and duration of physical activity with minimal burden on participants. The purpose of this study was to evaluate the absolute an d relative validity of three contemporary activity monitors (Computer Scien ce and Applications, Inc. [CSA], Tritrac, and Biotrainer) under both labora tory and field conditions. Methods: Fifty-two participants completed two 30 -min choreographed routines designed to simulate a variety of lifestyle phy sical activities. Three different treadmill paces were completed in both ro utines to evaluate reliability and validity under laboratory conditions. Si x different lifestyle activities were also examined to evaluate the validit y of the monitors under field conditions. During each routine, the activity levels of participants were monitored with the three activity monitors as well as by indirect calorimetry systems. Results: The correlations between the monitors and measured (V)over dotO(2) were higher for treadmill activit y (mean r = 0.86) compared with lifestyle activity (mean r = 0.55). Correla tions among the different monitors were high for both treadmill (r = 0.86) and lifestyle activities (r = 0.70), suggesting that the monitors provide s imilar information under both conditions. Under laboratory conditions, the CSA yielded accurate predictions of energy expenditure (EE), whereas the Tr itrac and Biotrainer tended to overestimate the EE (101-136% of measured va lue). The Tritrac, however, was found to have less error in individual esti mates of EE. Under field conditions, all of the monitors underestimated EE (range: 42-67% of measured value). Conclusion: The observed differences amo ng the monitors were attributed primarily to differences in the accuracy of the calibration equations rather than to the monitors themselves. Further research is needed to better understand how to use these devices for field- based assessments of physical activity.