Effects of body mass index on the accuracy of an electronic pedometer

Electronic pedometers are accurate for assessing steps taken while walking in normal weight adults but the accuracy of these devices has not been tested in overweight and obese men and women. The primary purpose of this study was to assess the accuracy of an electronic pedometer for measuring steps taken at various walking speeds in groups of adults with variations in body mass index (BMI). The secondary purpose was to determine if the manufacturer recommended position is the best placement position for overweight and obese adults. Participants were categorized into one of three BMI categories identified by the World Health Organization: normal (N = 25; < 25 kg x m(-2)), overweight (N = 24; 25 - 29.9 kg x m(-2)), or obese (N = 17; greater than or equal to 30 kg x m(-2)). Participants walked on a treadmill for 3 min at 54, 67, 80, 94, and 107m x min(-1) for a total of 15 min. During the treadmill walking, three electronic pedometers tallied steps taken. The pedometers were placed at the waist level, one on the anterior mid-line of the thigh (front; manufacturer recommended placement), one on the mid-axillary line (side), and one on the posterior mid-line of the thigh (back). Concurrently, a researcher counted steps using a hand-tally counter. Category of BMI did not affect the accuracy of the pedometer at any walking speed (54m x min(-1), p = 0.991; 67m x min(-1), P=0.556; 80m x min(-1), P=0.591; 94m x min(-1), p = 0.426; 107m x min(-1), p = 0.869). At 54m x min(-1), the front, side, and back pedometers significantly underestimated hand-tally counted steps by 20% (p < 0.001), 33% (p < 0.001), and 26% (p < 0.001), respectively. At 67m x min(-1) the front, side, and back pedometers significantly underestimated hand-tally counted steps by 7% (p = 0.027),13% (p < 0.001), 11% (p = 0.002), respectively. The steps recorded by the electronic pedometers placed at the front, side and back of the waist were not significantly different than steps counted by the hand-tally counter at speeds of 80m x min(-1) and higher for all subjects combined. An electronic pedometer accurately quantified steps walked at speeds of 80m x min(-1) or faster in persons with a normal BMI and those classified as overweight or obese. The placement of the pedometer on the front, side or back of the waistband did not affect accuracy of the pedometer for counting steps.