The Accuracy of the Placement of Wearable Monitors to Classify Sedentary and Stationary Time Under Free-Living Conditions

in Journal for the Measurement of Physical Behaviour
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Background: Published accelerometer cut-points have limited accuracy in measuring sedentary (SED) and stationary time (STA) despite hip or wrist placement. Few studies have evaluated established cut-points to measure SED and STA in free-living settings. Methods: This study evaluated published uniaxial and triaxial cut-points of accelerometers and identified optimal cut-points to measure SED and STA. Twenty participants, ages 18–65, wore three ActiGraph GT3X+ (one on each wrist and the waist) and two GENEActiv accelerometers (one on each wrist) for one weekday and one weekend day during simultaneous direct observation of movement. ActiGraph uniaxial cut-points (50, 100, 150, and 500 counts per minute [cpm]) and GENEActiv vector magnitude cut-points (VMCP; 217 and 386 cpm) were compared against the criterion measure of direct observation. As compared to the criterion, accuracy was determined with mean percent error, Bland-Altman plots, kappa coefficient, sensitivity, and specificity. Receiver operating characteristic curves identified cut-points with greatest discrimination to detect SED and STA. Results: For the GENEActiv, the 217 VMCP was most accurate for measuring SED and STA regardless of which arm wore the monitor. The ActiGraph was most accurate worn on the right hip using 100 and 150 uniaxial cpm to measure STA and 50 cpm to measure SED. Optimal ActiGraph VMCP cut-points to classify SED and STA were ActiGraph 2,000 cpm (left-wrist) and 63 cpm (right hip), respectively. Conclusion: Accuracy of ActiGraph uniaxial cut-points and GENEActiv VMCP is limited in assessing SED in free-living settings. Newer cut-points may increase the accuracy of measuring SED and STA from monitors in free-living settings.

Flórez-Pregonero is with the Departamento de Formación, Pontificia Universidad Javeriana, Bogota, Colombia. Buman and Ainsworth are with the College of Health Solutions, Arizona State University, Phoenix, AZ.

Ainsworth (Barbara.ainsworth@asu.edu) is corresponding author.

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