Precision and accuracy of an ankle-worn accelerometer-based pedometer in step counting and energy expenditure
Introduction
Obesity is epidemic in the United States and Europe and is emerging as a major health concern in low- and middle-income countries (World Health Organization, 1997). Statutory bodies and expert committees have repeatedly emphasized the importance of increasing physical activity because of the broad-ranging health benefits of exercise, even in the absence of weight loss (US Department of Health and Human Services CfDCaP, National Center for Chronic Disease Prevention and Health Promotion, 1996). How best to successfully promote physical activity, however, remains elusive (US Department of Health and Human Services CfDCaP, National Center for Chronic Disease Prevention and Health Promotion, 1996). One approach has been through using step-counting devices or pedometers. Pedometers, which are readily available and generally inexpensive, can either be used as a means of monitoring physical activity or for exercise treatment (“10,000 steps per day program”) (Tudor-Locke et al., 2002, Speck and Looney, 2001). Data suggest, however, (Melanson et al., 2004) that such devices are frequently inaccurate independent of user error. This is important because if pedometers prove to be inaccurate, we should be cautious regarding their use in detecting and treating inactivity.
In this paper, we investigate the precision and accuracy of an ankle-worn dual-axis accelerometer (Stepwatch) and investigate its potential application as a predictor of energy expenditure. Our primary hypothesis was that the Stepwatch pedometer is an accurate and precise measure of walking steps in lean and obese individuals. Our secondary hypothesis was that walking energy expenditure can be accurately modeled using the Stepwatch pedometer.
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Subjects
Twenty healthy adults of varying age (21–51 years), weight (56–120 kg), and body mass index (BMI) (19–43 kg/m2) were studied. Ten subjects (5 male and 5 female) were lean (BMI < 25 kg/m2) and 10 subjects (5 male and 5 female) were obese (BMI > 30 kg/m2).
Methods
Prior to the study, subjects provided informed verbal consent which was documented and all procedures were demonstrated and tested with the subject. The study was approved by the Mayo Clinic Institutional Review Board.
On the day of the study,
Results
All subjects completed all components of the study. The mean age, weight, and BMI (mean ± SD) for the lean group was 30 ± 13 years, 69 ± 11 kg, and 22 ± 2.0 kg/m2 and for the obese group (mean ± SD) 32 ± 7 years, 96 ± 12 kg, and 34 ± 4.0 kg/m2, respectively.
To address our primary hypothesis we compared the precision and accuracy of the pedometers against the gold standard of manual counting. First, there was almost perfect agreement between the two Stepwatches worn by each subject. The average,
Discussion
As obesity and inactivity are epidemic in many develop countries, we are challenged to develop accurate tools for evaluating and intervening in inactivity. Specifically, we evaluated an ankle-worn accelerometer-based step counter (the Stepwatch). We addressed two hypotheses, namely, that the Stepwatch is an accurate and precise measure of walking steps in lean and obese individuals. Our second hypothesis was that walking energy expenditure could be accurately modeled using the Stepwatch. Data
Acknowledgments
All authors declare no financial interest in any of the companies that manufacturer or distribute pedometers. The research was funded entirely by NIH DK56650, DK 63226, and DK66270.
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