Effects of Body Mass Index and Step Rate on Pedometer Error in a Free-Living Environment


Medicine & Science in Sports & Exercise:
doi: 10.1249/MSS.0b013e3181e9b133
Applied Sciences

Pedometers could provide great insights into walking habits if they are found to be accurate for people of all weight categories.

Purpose: The purposes of this study were to determine whether the New Lifestyles NL-2000 (NL) and the Digi-Walker SW-200 (DW) yield similar daily step counts as compared with the StepWatch 3 (SW) in a free-living environment and to determine whether pedometer error is influenced by body mass index (BMI) and speed of walking. The SW served as the criterion because of its accuracy across a range of speeds and BMI categories. Slow walking was defined as ≤80 steps per minute.

Methods: Fifty-six adults (mean ± SD: age = 32.7 ± 14.5 yr) wore the devices for 7 d. There were 20 normal weight, 18 overweight, and 18 obese participants. A two-way repeated-measures ANOVA was performed to determine whether BMI and device were related to number of steps counted per day. Stepwise linear regressions were performed to determine what variables contributed to NL and DW error.

Results: Both the NL and the DW recorded fewer steps than the SW (P < 0.001). In the normal weight and overweight groups, error was similar for the DW and NL. In the obese group, the DW underestimated steps more than the NL (P < 0.01). DW error was positively related to BMI and percentage of slow steps, whereas NL error was linearly related to percentage of slow steps. A surprising finding was that many healthy, community-dwelling adults accumulated a large percentage of steps through slow walking.

Conclusions: The NL is more accurate than the DW for obese individuals, and neither pedometer is accurate for people who walk slowly. Researchers and practitioners must weigh the strengths and limitations of step counters before making an informed decision about which device to use.

Author Information

Center for Physical Activity and Health, University of Tennessee, Knoxville, TN

Address for correspondence: Brian M. Tyo, Department of Exercise, Sport, and Leisure Studies, University of Tennessee, Knoxville, TN 37996; E-mail: btyo@utk.edu.

Submitted for publication January 2010.

Accepted for publication May 2010.

©2011The American College of Sports Medicine