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Test-retest reliability and minimum detectable change using the K4b2: oxygen consumption, gait efficiency, and heart
Benjamin J Darter1, Kelly M Rodriguez, Jason M Wilken
1Department of Physical Therapy, Virginia Commonwealth University, 1200 East Broad Street, P. O. Box 980224, Richmond, VA 23298, USA. bjdarter@vcu.edu
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.
