Wrist accelerometer cut-points for classifying sedentary behavior in children

van Loo, Christiana M.T. and Okely, Anthony D. and Batterham, Marijka J. and Hinkley, Trina and Ekelund, Ulf and Brage, Søren and Reilly, John J. and Trost, Stewart G. and Jones, Rachel A. and Janssen, Xanne and Cliff, Dylan P. (2017) Wrist accelerometer cut-points for classifying sedentary behavior in children. Medicine and Science in Sports and Exercise, 49 (4). pp. 813-822. ISSN 1530-0315 (https://doi.org/10.1249/MSS.0000000000001158)

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Introduction: To examine the validity and accuracy of wrist accelerometers for classifying sedentary behavior (SB) in children. Methods: Fifty-seven children (5-8y and 9-12y) completed a ~170min protocol including 15 semi-structured activities and transitions. Nine ActiGraph (GT3X+) and two GENEActiv wrist cut-points were evaluated. Direct observation was the criterion measure. The accuracy of wrist cut-points was compared to that achieved by the ActiGraph hip cut-point (≤25 counts/15s) and the thigh-mounted activPAL3™. Analyses included equivalence testing, Bland-Altman procedures and area under the receiver operating curve (ROC-AUC). Results: The most accurate ActiGraph wrist cut-points (Kim, vector magnitude: ≤3958 counts/60s and vertical axis: ≤1756 counts/60s) demonstrated good classification accuracy (ROC-AUC = 0.85-0.86) and accurately estimated SB time in 5-8y (equivalence p=0.02; mean bias: 4.1%, limits of agreement [LoA]: -20.1-28.4%) and 9-12y (equivalence p<0.01; - 2.5%, -27.9-22.9%). Mean bias of SB time estimates from Kim were smaller than ActiGraph hip (5-8y: 15.8%, -5.7-37.2%; 9-12y: 17.8%, -3.9-39.5%) and similar to or smaller than activPAL3™ 36 (5-8y: 12.6%, -39.8-14.7%; 9-12y: -1.4%, -13.9-11.0%), although classification accuracy was similar to ActiGraph hip (ROC-AUC = 0.85) but lower than activPAL3™ (ROC-AUC = 0.92-0.97). Mean bias (5-8y: 6.5%, -16.1-29.1%; 9-12y: 10.5%, -13.6-34.6%) for the most accurate GENEActiv wrist cut-point (Schaefer: ≤0.19g) was smaller than ActiGraph hip, and activPAL3™ in 5-8y, but larger than activPAL3™ 40 in 9-12y. However, SB time estimates from Schaefer were not equivalent to direct observation (equivalence p>0.05) and classification accuracy (ROC-AUC = 0.79-0.80) was lower than for ActiGraph hip and activPAL3™. Conclusion: The most accurate SB ActiGraph (Kim) and GENEActiv (Schaefer) wrist cut-points can be applied in children with similar confidence as the ActiGraph hip cut-point (≤25 counts/15s), although activPAL3™ was generally more accurate.