Reliability of the Actigraph GT3X+ Accelerometer in Adults under Free-Living Conditions

• Published in: PloS one Vol. 10; no. 8; p. e0134606
• Main Authors: Aadland, Eivind, Ylvisåker, Einar
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 14.08.2015; Public Library of Science (PLoS)
• Subjects: Accelerometers; Accelerometry - instrumentation; Accumulation; Actigraphy - instrumentation; Activities of daily living; Adult; Adults; Body mass; Body mass index; Body size; Computer science; Data reduction; Exercise; Female; Hip; Humans; Laboratories; Living conditions; Male; Motor Activity - physiology; Physical activity; Regression analysis; Regression models; Reliability analysis; Reliability aspects; Reproducibility of Results; Sedentary Lifestyle; Sports medicine; Statistical methods; Studies; Teacher education; Validity; Young Adult; United States > US; Norway
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0134606

Reliability of the Actigraph GT3X+ accelerometer has not been determined under normal wear time criteria in a large sample of subjects and accelerometer units. The aim of this study was to assess contralateral hip difference and inter-instrument reliability of the Actigraph GT3X+ monitor in adults under long-term free-living conditions. Eighty-seven adult subjects (28 men; mean (standard deviation) age 31.3 (12.2) years; body mass index 23.7 (3.1) kg/m2) concurrently wore two GT3X+ accelerometers (174 units in total) attached to contralateral hips for 21 days. Reliability was assessed using Bland-Altman plots, mixed model regression analyses and absolute measures of agreement for different lengths of data accumulation (single-day-, 7-day- and 21-day periods). There were no significant differences between contralateral hips (effect size ≤0.042; p ≥.213). Inter-instrument reliability increased with increased length of data-accumulation. For a 7-day measurement period (n = 232 weeks), limits of agreement were ±68 cpm (vertical axis) and ±81.3 cpm (vector magnitude) for overall physical activity (PA) level, ±51 min for sedentary time, ±18.2 min for light PA, ±6.3 min for moderate PA, ±3.5 min for vigorous PA, and ±6.7 min for moderate-to-vigorous PA. The Actigraph GT3X+ accelerometer is a reliable tool for measuring PA in adults under free-living conditions using normal data-reduction criteria. Contralateral hip differences are very small. We suggest accelerometers be attached to the right hip and data to be accumulated over several days of measurement.