Accuracy of the Omron HJ-720ITC in Free-Living Individuals

The primary purpose of this investigation was to examine the accuracy of the Omron HJ- 720ITC piezo-electric pedometer in a free-living environment over a 24-hr period across 3 different BMI categories. A secondary purpose was to compare the accuracy the Omron HJ- 720ITC to that of a spring-levered pedometer (Yamax SW-200). 62 adult volunteers were placed in 3 BMI categories: Normal weight (N=19), Overweight (N=23), or Obese (N=23). Subjects wore five devices over a 24-hr period except when bathing or sleeping. The criterion pedometer (StepWatch-3) was worn on the lateral side of the right ankle. The Omron HJ-720ITC was worn in the mid-line of the right thigh, in the right pants pocket and on a lanyard around the neck. A comparison pedometer (Yamax SW-200) was worn on the belt, in mid-line of the left thigh. The Omron HJ-720ITC significantly underestimated steps taken per day in all three BMI categories compared to the criterion measure (P < 0.001). The pocket position demonstrated mean percent errors in normal, overweight and obese BMI categories of -31.7%, -29.8%, and -35.1% respectively, and was the most accurate in obese individuals. However, in normal and overweight individuals, the Omron in each position was less accurate than the Yamax pedometer. (MPE = -19% and -21%). The Omron HJ-720ITC pedometer is a valid instrument for step counting during continuous walking bouts. However, the Omron significantly underestimates the number of steps taken in free-living individuals. A 4-second step filter that determines walking pattern may contribute to an underestimation of steps accumulated through light, intermittent activity.