Martin Luther King Jr. DayOur office will be closed Monday, January 17th in observance of Martin Luther King Jr. Day. We will reopen at regular business hours on Tuesday, January 18th.
ActiGraph GT3X+ cut-points for identifying sedentary behaviour in older adults in free-living environments
- Published on Aug. 8, 2013
Objectives To determine the ActiGraph GT3X+ cut-points with the highest accuracy for estimating time spent in sedentary behaviour in older adults in free-living environments. ActivPAL3™ was used as the reference standard.
Design Cross-sectional study.
Methods 37 participants (13 males and 24 females, 73.5±7.3 years old) wore an ActiGraph GT3X+ and an ActivPAL3™ for 7 consecutive days. For ActivPAL3™, variables were created based on posture. For ActiGraph GT3X+, sedentary behaviour was defined as (1) vector magnitude and (2) vertical axis counts for 1-s, 15-s and 1-min epochs, with cut-points for 1-s epochs of <1 to <10counts, for 15-s epochs of <1 to <100counts and for 1-min epochs of <1 to <400counts. For each of the ActiGraph GT3X+ cut-points, area under the receiver operating characteristic curve (area under the curve), sensitivity, specificity, and percentage correctly classified were calculated. Bias and 95% limits of agreement were calculated using the Bland-Altman method.
Results The highest areas under the curve were obtained for the vector magnitude cut-points: <1count/s, <70counts/15-s, and <200counts/min; and for the vertical axis cut-points: <1count/s, <10counts/15-s and <25counts/min. Mean biases ranged from -4.29 to 124.28min/day. The 95% limits of agreement for these cut-points were ±2h suggesting great inter-individual variation.
Conclusions The results suggest that cut-points are dependent on unit of analyses (i.e. epoch length and axes); cut-points for a given epoch length and axis cannot simply be extrapolated to other epoch lengths. Limitations regarding inter-individual variability and misclassification of standing activity as sitting/lying must be considered.