Introduction: The primary purpose of this study was to examine the accuracy of the Omron HJ-720ITC piezoelectric pedometer in a free-living environment during a 24-h period. A secondary purpose was to compare the accuracy the Omron to that of a spring-levered pedometer.
Methods: A total of 62 adult volunteers were classified according to body mass index (BMI) category: normal weight (n = 19), overweight (n = 23), and obese (n = 20). Subjects wore five devices during a 24-h period except when bathing or sleeping. The criterion pedometer (StepWatch-3) was worn on the lateral side of the right ankle. Omron HJ-720ITC pedometers were worn in three locations: (a) on the belt, (b) in the pants pocket, and (c) on a lanyard around the neck. A comparison pedometer (Yamax SW-200) was worn on the belt.
Results: The Omron HJ-720ITC underestimated the steps per day in all three BMI categories compared with the criterion measure (P < 0.05). The Omron was most accurate in the pocket location, recording 68%, 70%, and 65% of steps in the normal, overweight, and obese BMI categories, respectively. In the obese group, the Omron was more accurate than the Yamax pedometer, but in the normal and overweight groups, it was less accurate than the Yamax.
Conclusions: Results from our study show that the Omron significantly underestimates steps per day under free-living conditions. This is due, in part, to the presence of a 4-s step filter that contributes to an underestimation of steps accumulated during intermittent activities. In the pocket, the Omron accuracy was similar for lean, overweight, and obese individuals. In contrast, the accuracy of the Yamax pedometer declined with increasing BMI categories.