Comparison of two physical activity monitors during a 1-mile walking field test

This study assessed the relationship of two different accelerometer devices to oxygen consumption (VO₂) during the performance of the Rockport Fitness Walking Test under field conditions. Forty-three healthy subjects (28 female, 15 male) aged 40-59 years (mean = 52 ± 7.7 years) participated in the study. Energy expenditure was measured simultaneously using the Caltrac and BioTrainer accelerometers and VO₂ measured with the AeroSport KB-1 system. Pearson r correlations were calculated to determine the relationships between the measures. Accuracy of the accelerometers to VO₂ was determined using one-way repeated measures ANOVA, Bland-Altman plots and the SEE. Significant correlations (p < 0.004) were found between the energy expenditure measures obtained by 1) VO₂ and the Caltrac (r = 0.67), 2) VO₂ and the BioTrainer (r = 0.43) and 3) Caltrac and BioTrainer accelerometers (r = 0.70). However, both accelerometers overestimated caloric expenditure by about 50% with a large SEE noted; 14.0 Kcals and 16.9 Kcals for the Caltrac and BioTrainer accelerometers respectively. Though our results show fair to moderate correlations (r = 0.43 - 0.67) between the accelerometers and VO₂ during level walking under field conditions, the accuracy of the accelerometers in predicting energy expenditure was poor. Accelerometers may prove to be an inexpensive and reliable means of tracking client progress, however until better activity specific regression equations are established, practitioners must be aware that accelerometers may not be accurate in estimating energy expenditure.