The purpose of the present study was to derive linear and non-linear regression equations that estimate energy expenditure (EE) from triaxial accelerometer counts that can be used to quantitate activity in young children. We are unaware of any data regarding the validity of triaxial accelerometry for assessment of physical activity intensity in this age group. EE for 27 girls and boys (6.0 +/- 0.3 years) was assessed for nine activities (lying down, watching a video while sitting and standing, line drawing for coloring-in, playing blocks, walking, stair climbing, ball toss, and running) using indirect calorimetry and was then estimated using a triaxial accelerometer (ActivTracer, GMS). Significant correlations were observed between synthetic (synthesized tri-axes as the vector), vertical, and horizontal accelerometer counts and EE for all activities (0.878 to 0.932 for EE). However, linear and non-linear regression equations underestimated EE by >30% for stair climbing (up and down) and performing a ball toss. Therefore, linear and non-linear regression equations were calculated for all activities except these two activities, and then evaluated for all activities. Linear and non-linear regression equations using combined vertical and horizontal acceleration counts, synthetic counts, and horizontal counts demonstrated a better relationship between accelerometer counts and EE than did regression equations using vertical acceleration counts. Adjustment of the predicted value by the regression equations using the vertical/horizontal counts ratio improved the overestimation of EE for performing a ball toss. The results suggest that triaxial accelerometry is a good tool for assessing daily EE in young children.
