The Effect of Body Mass Index on Pedometer Accuracy in a Free-Living Environment

The purpose of this dissertation was to determine if the New Lifestyles NL-2000 (NL) and the Digi-Walker SW-200 (DW), waist-mounted devices, yield similar daily step counts as compared to the StepWatch 3 (SW), an ankle-mounted device, worn by adults and children in the free-living environment.

For the first study, fifty-six adults (32.7 + 14.5 y) wore the devices for seven consecutive days. There were 20 normal weight, 18 overweight, and 18 obese participants. The NL and DW undercounted (pedometer error) similarly in the normal weight and overweight groups (-15.4% to -18.2%, respectively). However, the DW undercounted more than the NL in the obese group (-32.8% vs -23.9%, respectively). Stepwise regression revealed that both the NL and DW had more error (undercounted more) as a greater percentage steps were accumulated while walking slowly. The DW also had more error with greater BMI. Use of the DW in an obese population will result in twice the error as compared to a normal weight population and thus the DW should not be used to determine relationships between walking volume and adiposity

For the second study, 74 children (13 ± 1.1 y) wore the same devices during one weekday. There were 33 normal weight, 21 overweight, and 20 obese participants. The error was determined for the NL and DW, and the values were similar in the normal weight and overweight groups (-10.8% to -15.4%, respectively). The DW undercounted more than the NL in the obese group (-27.3% vs -8.4%, respectively). The NL was very consistent regardless of BMI category, recording 89.1% (-10.8% error), 89.1% (-10.9% error), and 91.6% (-8.4% error) for the normal weight, overweight, and obese participants, respectively. Stepwise regression revealed that the DW undercounted more in participants with a high weight. Using the DW in obese children of this age group will result in significantly more undercounting when compared to normal weight children. The DW should not be used to determine relationships between walking volume and adiposity in this population. The NL undercounted by ~10%, regardless of BMI category.