Comparison of GT3X Accelerometer and YAMAX Pedometer Steps/Day in a Free-Living Sample of Overweight and Obese Adults

Background: The purpose of this study was to compare steps/day detected by the YAMAX SW-200 pedometer versus the Actigraph GT3X accelerometer in free-living adults. Methods: Daily YAMAX and GT3X steps were collected from a sample of 23 overweight and obese participants (78% female; age = 52.6 +/- 8.4 yr.; BMI = 31.0 +/- 3.7 m.kg(-2)). Because a pedometer is more likely to be used in a community-based intervention program, it was used as the standard for comparison. Percent difference (PD) and absolute percent difference (APD) were calculated to examine between-instrument agreement. In addition, days were categorized based on PD: a) under-counting (> -10 PD), b) acceptable counting (-10 to 10 PD), and 9) over-counting (> 10 PD). Results: The YAMAX and GT3X detected 8,025 +/- 3,967 and 7131 +/- 3066 steps/day, respectively, and the outputs were highly correlated (r = .87). Average PD was -3.1% +/- 30.7% and average APD was 23.9% +/- 19.4%. Relative to the YAMAX, 53% of the days detected by the GT3X were classified as under-counting, 25% acceptable counting, and 23% over-counting. Conclusion: Although the output of these 2 instruments is highly correlated, caution is advised when directly comparing or using their output interchangeably.