Validity of hip-mounted uniaxial accelerometry with heart-rate monitoring vs. triaxial accelerometry in the assessment of free-living energy expenditure in young children: the IDEFICS Validation Study.

One of the aims of Identification and Prevention of Dietary- and Lifestyle-Induced Health Effects in Children and Infants (IDEFICS) validation study is to validate field measures of physical activity (PA) and Energy expenditure (EE) in young children. This study compared the validity of uni-axial accelerometry with heart-rate (HR) monitoring vs. tri-axial accelerometry against doubly labeled water (DLW) criterion method for assessment of free-living EE in young children. 49 European children (25 female, 24 male) aged 4-10 years (mean age 7 +/- 2 years) were assessed by uni-axial ActiTrainer with HR, uni-axial 3DNX and tri-axial 3DNX accelerometry. Total energy expenditure (TEE) was estimated using DLW over a 1 week period. The longitudinal axis of both devices and tri-axial 3DNX counts per minute (CPM) were significantly (P<0.05) associated with physical activity level (PAL) (r = 0.51 ActiTrainer, r = 0.49 uni-axial-3DNX and r = 0.42 tri-axial summation operator3DNX). 86% of the variance in TEE could be predicted by a model combining body mass (Partial r(2) = 71%; P<0.05), CPM-ActiTrainer (Partial r(2) = 11%; P<0.05) and difference between HR at moderate and sedentary activities (ModHR - SedHR; Partial r(2) = 4%; P<0.05) The standard error (S.E) of TEE estimate for ActiTrainer and 3DNX models ranged from 0.44-0.74 MJ/d or approximately 7-11% of the average TEE. The S.E of activity-induced energy expenditure (AEE) model estimates ranged from 0.38-0.57 MJ/d or 24-26% of the average AEE. It is concluded that the comparative validity of hip-mounted uni-axial and tri-axial accelerometers for assessing PA and EE is similar.