Comparison of two Actigraph models for assessing free-living physical activity in Indian adolescents

This aim of this study was to compare the new Actigraph ( GT1M) with the widely used Model 7164. Seven days of free-living physical activity were measured simultaneously using both the Model 7164 and GT1M in 30 Indian adolescents ( mean age 15.8 years, s 0.6). The GT1M was on average 9% lower per epoch than model 7164, thus a correction factor of 0.91 is suggested for comparison between the two monitors. The differences between monitors increased in magnitude with intensity of activity ( P<0.001) but remained randomly distributed ( r= 0.01, P= 0.96). No significant difference was observed between monitors for time spent in moderate ( P = 0.31) and vigorous ( P= 0.34) physical activity when using the same epoch length. The Model 7164 classified less time as sedentary ( P<0.001) and more time as light- intensity activity ( P<0.001) than the GT1M. In conclusion, data from the GT1M can be compared with historical data using average counts per minute with a correction factor, and the two models might be comparable for assessing time spent in moderate to vigorous physical activity in children when using the same epoch length.