Wrist Accelerometer Cut Points for Classifying Sedentary Behavior in Children

Abstract

Introduction: This study aimed to examine the validity and accuracy of wrist accelerometers for classifying sedentary behavior (SB) in children.

Methods: Fifty-seven children (5-8 and 9-12 yr) completed an ~170-min protocol, including 15 semistructured 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 with that achieved by the ActiGraph hip cut point (≤25 counts per 15 s) 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 per 60 s; vertical axis, ≤1756 counts per 60 s) demonstrated good classification accuracy (ROC-AUC = 0.85-0.86) and accurately estimated SB time in 5-8 yr (equivalence P = 0.02; mean bias = 4.1%, limits of agreement = -20.1% to 28.4%) and 9-12 yr (equivalence P < 0.01; -2.5%, -27.9% to 22.9%). The mean bias of SB time estimates from Kim were smaller than ActiGraph hip (5-8 yr: 15.8%, -5.7% to 37.2%; 9-12 yr: 17.8%, -3.9% to 39.5%) and similar to or smaller than activPAL3 (5-8 yr: 12.6%, -39.8% to 14.7%; 9-12 yr: -1.4%, -13.9% to 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 (5-8 yr: 6.5%, -16.1% to 29.1%; 9-12 yr: 10.5%, -13.6% to 34.6%) for the most accurate GENEActiv wrist cut point (Schaefer: ≤0.19 g) was smaller than ActiGraph hip, and activPAL3 in 5-8 yr, but larger than activPAL3 in 9-12 yr. 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 per 15 s), although activPAL3 was generally more accurate.

Figure 1. 95% equivalence test for accelerometry-based estimated time spent in sedentary behaviors in 5-8 year-olds.

Times estimated by wrist-worn ActiGraph and wrist-worn GENEActiv cut-points are equivalent to direct observation if 90% confidence intervals lie entirely within the equivalence region of direct observation.VA: vertical axis; VM: vector magnitude; SVM: gravity-subtracted signal vector magnitude; ROC: developed using receiver operating curve analysis; Regression: developed using regression analysis.

Figure 2. 95% equivalence test for accelerometry-based estimated time spent in sedentary behaviors in 9-12 year-olds.

Times estimated by wrist-worn ActiGraph and wrist-worn GENEActiv cut-points are equivalent to direct observation if 90% confidence intervals lie entirely within the equivalence region of direct observation. VA: vertical axis; VM: vector magnitude; SVM: gravity-subtracted signal vector magnitude; ROC: developed using receiver operating curve analysis; Regression: developed using regression analysis.