Performance of the Wrist-worn Actigraph GT3X + in Measuring Physical Activity in Older Women

Introduction: Being able to accurately measure physical activity intensity and energy expenditure is crucial to understanding the role physical activity plays in lowering the risk for disease. This thesis aims to examine the performance of the wrist-worn GT3X+ in measuring PAEE and classifying activity intensity in a healthy non-obese population of older women. Methods: Baseline data collected in the Women’s Energy Expenditure in Walking Programs Study (ClinicalTrials.gov identifier: NCT01722136) were used. PAEE was measured concurrently for 2 weeks using the doubly labeled water method in combination with indirect calorimetry, the GT3X+ ActiGraph accelerometer (GT3X+, ActiGraph LLC, Pensacola, FL), and the SenseWear Armband Mini monitor (SWAM, BodyMedia Inc. Pittsburgh, PA, USA). Results: The GT3X+ showed a moderate correlation with the SWAM and DLW and IC in measuring PAEE. When estimating time spent in activity intensity, the GT3X+ underestimated sedentary time and overestimated activity intensity when compared to the SWAM. Furthermore, during the Epoch by Epoch analysis, the GT3X+ misclassified light intensity activity as MVPA 71.96% of the time. Conclusion: The currently available PAEE estimation equations do not allow us to accurately measure PAEE with the wrist-worn GT3X+ in a population of older women. Furthermore, when compared to the SWAM, the cut points available for the GT3X+ tend to overestimate time spent in light intensity activity and MVPA and underestimate sedentary time when worn on the wrist.