Purpose: The objective of this study is 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 and thirty-one youth between the ages of 10–17 yr and BMI from 15 to 44 kg·m−2 were outfitted with hip-worn ActiGraph GT1M (Pensacola, FL), Actical (MiniMiter/Respironics, Bend, OR), and RT3 (StayHealthy, Monrovia, CA) accelerometers and spent approximately 24 h 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 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 underpredicted 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 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 with both criterion measurement and each other, which poses a potential difficulty for interstudy (e.g., different accelerometers) and intrastudy (e.g., BMI and adiposity) comparisons.
1Division of Gastroenterology, Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN; 2Vanderbilt Institute for Energy and Environment, Climate Change Research Network, Vanderbilt University, Nashville, TN; 3Division of Gastroenterology, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN; 4Department of Biostatistics, Vanderbilt University Medical Center, Nashville, TN; and 5National Institute of Diabetes and Digestive and Kidney Disease/Diabetes, Endocrinology, and Obesity Branch, National Institutes of Health, Bethesda, MD
Address for correspondence: Maciej S. Buchowski, Ph.D., Division of Gastroenterology, Hepatology and Nutrition, Department of Medicine, Vanderbilt University Medical Center, 1161 21st Avenue South, MedicalCenter North, Room A4103, Nashville, TN 37232-2260; E-mail: email@example.com.
Submitted for publication March 2012.
Accepted for publication June 2012.
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