Estimating Energy Expenditure With the RT3 Triaxial Accelerometer

Abstract

The RT3 is a relatively new triaxial accelerometer that has replaced the TriTrac. The aim of this study was to validate the RT3 against doubly labeled water (DLW) in a free-living, mixed weight sample of adults. Total energy expenditure (TEE) was measured over a 15-day period using DLW. Activity-related energy expenditure (AEE) was estimated by subtracting resting energy expenditure and thermic effect of feeding from TEE. The RT3 triaxial accelerometer was worn over 14 consecutive days. TEE and AEE were estimated using the RT3 proprietary equation. Thirty-six adults ages 18–56 years (56% women) with an average weight of 75.9 kg (SD = 14.8) completed all measurements. Compared to DLW, the RT3 underestimated TEE by 539 kJ (4%) and AEE by 485 kJ (15%) on average. The RT3 provided a relatively accurate assessment of free-living activity-related energy expenditure at the group level and generally underestimated total and activity-related energy expenditure compared to DLW.

Key words:

• physical activity
• activity counts
• motion sensor
• body composition

Additional information

Notes on contributors

Ralph Maddison

This was an investigator-initiated study conducted in collaboration with the Harvard School of Public Health and funded as a subcomponent of a National Institutes of Health research grant. Authors Maddison and Lawes were supported by National Heart Foundation of New Zealand Research Fellowships. The authors have no professional relationships with companies or manufacturers, and the results of the present study do not constitute the authors' endorsement of the product. We wish to thank IsoTrace NZ Ltd. for their technical assistance with the doubly labeled water measurements, Joshua Salomon at Harvard University for contributing to the study design and methodology, and all the participants who took part in this study. Please address all correspondence concerning this article to Ralph Maddison, Clinical Trials Research Unit, University of Auckland, Private Bag 92019, Auckland, New Zealand.