COMPARISON OF ENERGEY EXPENDITURE ESTIMATED BY BI-AXIAL ACCELEROMETRY TO INDIRECT CALORIMETRY

Abstract

The BioTrainer-Pro Professional Exercise Monitor (IM Systems, Baltimore MD) is a bi-axial accelerometer developed through NIH SBIR funding support and capable of storing up to 112 days of data. Only one published scientific study aimed to validate the accelerometer and reported that the BioTrainer (BT) overestimated energy expenditure in the laboratory and underestimated energy expenditure in a field setting (Welk, 2000). PURPOSE The purpose of this study was to evaluate the ability of the BT to accurately estimate energy expenditure (EE) during treadmill exercise compared to criterion EE measures determined from indirect calorimetry. METHODS A total of 10 male and 10 female apparently healthy adults [mean (SE) age; 26.7 (0.5) y] performed 10 minutes of treadmill walking at 53.6, 80.4, and 107.2 m/min and treadmill running at 134.0, 160.8, 187.6, and 214.4 m/min. Accelerometers were placed bilaterally at the waist in the posterior axillary position, one on each side of the body. Simultaneous measurements of accelerometry and indirect calorimetry were continuously recorded during exercise. Data were analyzed with repeated measures Analysis of Variance and pairwise Bonferroni-adjusted estimated marginal means. RESULTS There was no significant difference (P > 0.36) between bilateral mean EE recorded by the BT at any treadmill speed. Below 134.0 m/min, the mean EE recorded by the BT increased significantly (P < 0.001) with subsequent treadmill speeds. However, there was no significant difference (P > 0.18) in mean EE recorded by the BT between speeds at or above 134.0 m/min. Additionally, compared to indirect calorimetry, the BT overestimated EE at all seven treadmill speeds [mean (SE) difference for all speeds; 5.0 (0.6) kcal/min, P < 0.01] with the greatest magnitude of difference at 134.0 m/min (range; 30.9–53.7%). CONCLUSION These data suggest that the BT significantly overestimates EE during treadmill exercise compared to indirect calorimetry and that the BT was not sensitive to changes in running speed above 134.0 m/min.