Test–Retest Reliability and Minimum Detectable Change Using the K4b²: Oxygen Consumption, Gait Efficiency, and Heart Rate for Healthy Adults During Submaximal Walking

Abstract

Purpose: Oxygen consumption (VO₂; mLO₂/kg/min), gait efficiency (GE; mlO₂/kg/m) and heart rate (HR; beats per minute) are measures of physiological gait performance. However, the collection device, procedures for data normalization, and biological factors can affect measurement variability. The purpose of this study was to determine the test–retest reliability and minimum detectable change (MDC) for VO₂, GE, and HR with the K4b² at submaximal walking speeds in healthy young adults. A second purpose was to determine if net measures improved reproducibility. Method: Twenty-two participants completed 2 identical treadmill tests on separate days at submaximal walking speeds from 0.71 m/s to 1.65 m/s. Results: Intraclass correlation coefficient (ICC) values for gross VO₂, gross GE, and HR were greater than .85 for all walking speeds. Associated MDC values were approximately 7% to 10% for gross VO₂ and GE, and approximately 9% to 12% for HR. ICC values for resting VO₂ were lower, with MDC values approaching 25%. Subtracting out resting values to derive net VO₂ and GE values produced ICC values below .76 for the 2 slowest speeds but ICC values greater than .83 for the faster speeds. MDC values for net VO₂ and GE were up to 20% for the slowest speeds. Conclusions: The results demonstrate metabolic cost can be assessed reliably using the K4b² during submaximal walking and that gross measures are more reliable than net measures. Furthermore, changes at self-selected speeds exceeding 1.0 mLO₂/kg/min in gross VO₂ and 0.01 mLO₂/kg/m in gross GE can be considered a true change in walking performance.

Keywords:

• exercise test
• gait
• reproducibility of results

Acknowledgments

The view(s) expressed herein are those of the author(s) and do not reflect the official policy or position of Brooke Army Medical Center, the U.S. Army Medical Department, the U.S. Army Office of the Surgeon General, the Department of the Army, Department of Defense, the U.S. government, or the National Institutes of Health.

  The participants were enrolled in studies approved by the institutional review board at Brooke Army Medical Center in Ft. Sam Houston, TX (C.2008.174).

  Support for this project was provided by the Military Amputee Research Program through grant awards to the authors (BJD, JMW) and by Clinical and Translational Science Award No. KL2TR000057 from the National Center for Advancing Translational Sciences (BD).

  We, the authors, affirm that we have no financial affiliation (including research funding) or involvement with any commercial organization that has a direct financial interest in any matter included in this manuscript.