Effect of BMI on Prediction of Accelerometry-Based Energy Expenditure in Youth

Purpose To determine the effect of body mass index (BMI) on level of agreement between six previously established prediction equations for three commonly used accelerometers to predict summary measures of energy expenditure (EE) in youth.

Methods One hundred thirty-one youth between the ages of 10-17 years and BMI from 15 to 44 kg/m² were outfitted with hip-worn ActiGraph GT1M, Actical, and RT3 accelerometers and spent approximately 24 hours in a whole-room indirect calorimeter while performing structured and self-selected activities. Five commonly used regression and one propriety equations for each device were used to predict the minute-to-minute EE (normalized to metabolic equivalents, METs), daily physical activity level (PAL), and time spent in sedentary, light, moderate, and vigorous physical activity intensity categories. The calculated values were compared with criterion measurements obtained from the room calorimeter.

Results All predictive equations, except RT3, significantly over- or under-predicted daily PAL (p < 0.001), with large discrepancies observed in the estimate of sedentary and light activity. Discrepancies between actual and estimated PAL ranged from 0.05 to 0.68. In addition, BMI represented a modifier for two ActiGraph predictive equations (AG1 and AG2), affecting the accuracy of physical activity-related EE (PAEE) predictions.

Conclusion ActiGraph (AG3) and the RT3 closely predicted overall PAL (within 4.2 and 6.8%, respectively) as a group. When adjusting for age, sex, and ethnicity, Actical (AC1 and AC2) and ActiGraph (AG3) were not influenced by BMI. However, a gap between some hip-worn accelerometer predictive and regression equations was demonstrated compared to both criterion measurement and each other, which poses a potential difficulty for inter-study (e.g. different accelerometers) and intra-study (e.g., BMI, adiposity) comparisons.

Link to Abstract: http://journals.lww.com/acsm-msse/Abstract/2012/12000/Effect_of_BMI_on_Prediction_of_Accelerometry_Based.22.aspx