Age-Group Comparability of Raw Accelerometer Output from Wrist- and Hip-Worn Monitors

Purpose: The study aims were to compare raw tri-axial accelerometer output from ActiGraph GT3X + (AG) and GENEActiv (GA) placed on the hip and the wrist and to develop regression equations for estimating energy expenditure.

Methods: Thirty children (7-11 yr.) and 30 adults (18-65 yr.) completed eight activities (ranging from lying to running) whilst wearing one AG and one GA on the hip and the wrist. Oxygen consumption (VO2) was measured with indirect calorimetry. Analysis involved the use of ANOVA to examine the effect of activity, brand and placement on the acceleration values, ICC to evaluate the agreement between the two brands and placements and linear regression to establish intensity thresholds.

Results: A significant difference in acceleration values between the hip and the wrist placement was found (p < 0.001). The output from the wrist placement was in general higher compared to the hip. There was no main effect of monitor brand in adults (p < 0.12) and children (p < 0.73) and the ICC showed a strong agreement (0.96-0.99). However, a three-way interaction and systematic error between the brands was found in children. Acceleration from both brands and placements showed a strong correlation with VO2. The intensity classification accuracy of the developed thresholds for both brands and placements were in general higher for adults compared to children and were greater for sedentary/light (93-97%), and vigorous activities (68-92%), than moderate activities (33-59%).

Conclusions: Accelerometer output from AG and GA appears comparable when attached to the same body location in adults, whereas non-consistent differences are apparent between the two brands and placements in children, hence limiting the comparability between brands in this age group.