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PLoS One





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Background: Public health research on sedentary behavior (SB) in youth has heavily relied on accelerometers. However, ithas been limited by the lack of consensus on the most accurate accelerometer cut-points as well as by unknown effectscaused by accelerometer position (wrist vs. hip) and output (single axis vs. multiple axes). The present study systematicallyevaluates classification accuracy of different Actigraph cut-points for classifying SB using hip and wrist-worn monitors andestablishes new cut-points to enable use of the 3-dimensional vector magnitude data (for both hip and wrist placement).
Methods: A total of 125 children ages 7–13 yrs performed 12 randomly selected activities (from a set of 24 differentactivities) for 5 min each while wearing tri-axial Actigraph accelerometers on both the hip and wrist. The accelerometer datawere categorized as either sedentary or non-sedentary minutes using six previously studied cut-points: 100counts-per-minute (CPM), 200CPM, 300CPM, 500CPM, 800CPM and 1100CPM. Classification accuracy was evaluated with Cohen’s Kappa(k) and new cut-points were identified from Receiver Operating Characteristic (ROC).
Results: Of the six cut-points, the 100CPM value yielded the highest classification accuracy (k = 0.81) for hip placement. Forwrist placement, all of the cut-points produced low classification accuracy (ranges of k from 0.44 to 0.67). Optimal sedentarycut-points derived from ROC were 554.3CPM (ROC-AUC of 0.99) for vector magnitude for hip, 1756CPM (ROC-AUC of 0.94)for vertical axis for wrist, and 3958.3CPM (ROC-AUC of 0.93) for vector magnitude for wrist placement.
Conclusions: The 100CPM was supported for use with vertical axis for hip placement, but not for wrist placement. The ROC-derived cut-points can be used to classify youth SB with the wrist and with vector magnitude data.


© 2014 Kim et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and source are credited.