Accelerometer Data Processing and Energy Expenditure Estimation in Preschoolers

Purpose To assess the capacity of different acceleration metrics from wrist accelerations to estimate total and activity energy expenditure (TEE, AEE) using doubly labelled water (DLW) in preschool children. Methods Thirty-nine preschoolers (5.5±0.1 years) were included. TEE was measured using DLW during 14 days and AEE was then calculated using a predicted basal metabolic rate. Participants wore a wGT3X-BT accelerometer on their non-dominant wrist for ≥5 days. We derived the following metrics from raw accelerations: raw ActiGraph activity counts using the normal filter (NFCounts) and the low-frequency extension (LFECounts); and alternate summary metrics such as the Euclidian norm minus 1 g (ENMO), Euclidian norm of the high-pass filtered accelerations (HFEN), the band-pass filtered accelerations (BFEN), the HFEN plus Euclidean norm of low-pass filtered accelerations minus 1 g (HFEN+) and the mean amplitude deviation (MAD). Results Alternate summary metrics explained a larger proportion of the variance in TEE and AEE than ActiGraph's activity counts (counts: 7-8 and 25% of TEE and AEE; alternate summary metrics: 13-16% and 35-39% of TEE and AEE). Adjustments for body weight and height resulted in an explanation of 51% of AEE by ENMO. All of the metrics adjusted for fat mass (FM) and fat-free mass (FFM) explained up to 84% and 67% of TEE and AEE, respectively. Conclusions ENMO and the other alternate summary metrics explained more of the variance in TEE and AEE than the ActiGraph's activity counts in five-year-old children, suggesting further exploration of these variables in studies on physical activity and energy expenditure in preschoolers. Our results need confirmation in other populations with wider age groups and varying body compositions. Corresponding author: Jairo Hidalgo Migueles, Carretera de Alfacar, S/N. 18071 Granada. (+34) 958 24 43 53. jairohm@ugr.es This study was conducted under the umbrella of the MINISTOP project (Principal investigator ML). The MINISTOP study was funded by the Swedish Research Council (project no. 2012–2883), the Swedish Research Council for Health, Working Life and Welfare (2012-0906), Bo and Vera Axson Johnsons Foundation and Karolinska Institutet (all ML). JHM was supported by a Grant from the Spanish Ministry of Education, Culture and Sport (FPU15/02645); CDN by the Henning and Johan Throne-Holst Foundation; PH by a grant from the Strategic Research Area Health Care Science, Karolinska Institutet/Umeå University; CC-S by the Spanish Ministry of Economy and Competitiveness (BES-2014-068829). Francisco B. Ortega by the Spanish Ministry of Science and Innovation (RYC-2011-09011). Additional funding was obtained from the University of Granada, Plan Propio de Investigación 2016, Excellence actions: Units of Excellence; Unit of Excellence on Exercise and Health (UCEES). This is part of a PhD Thesis conducted in the Biomedicine Doctoral Studies at the University of Granada, Spain. Conflict of interest: The results of the present study do not constitute endorsement by ACSM. We declare that the results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. Accepted for Publication: 28 September 2018 © 2018 American College of Sports Medicine

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