title: Actigraph GT3X: validation and determination of physical activity intensity cut points.
abstract: The aims of this study were: to compare energy expenditure (EE) estimated from the existing GT3X accelerometer equations and EE measured with indirect calorimetry; to define new equations for EE estimation with the GT3X in youth, adults and older people; and to define GT3X vector magnitude (VM) cut points allowing to classify PA intensity in the aforementioned age-groups. The study comprised 31 youth, 31 adults and 35 older people. Participants wore the GT3X (setup: 1-s epoch) over their right hip during 6 conditions of 10-min duration each: resting, treadmill walking/running at 3, 5, 7, and 9 km · h⁻¹, and repeated sit-stands (30 times · min⁻¹). The GT3X proved to be a good tool to predict EE in youth and adults (able to discriminate between the aforementioned conditions), but not in the elderly. We defined the following equations: for all age-groups combined, EE (METs)=2.7406+0.00056 · VM activity counts (counts · min⁻¹)-0.008542 · age (years)-0.01380 ·  body mass (kg); for youth, METs=1.546618+0.000658 · VM activity counts (counts · min⁻¹); for adults, METs=2.8323+0.00054 · VM activity counts (counts · min⁻¹)-0.059123 · body mass (kg)+1.4410 · gender (women=1, men=2); and for the elderly, METs=2.5878+0.00047 · VM activity counts (counts · min⁻¹)-0.6453 · gender (women=1, men=2). Activity counts derived from the VM yielded a more accurate EE estimation than those derived from the Y-axis. The GT3X represents a step forward in triaxial technology estimating EE. However, age-specific equations must be used to ensure the correct use of this device.
authors.affiliation: Faculty of Health Science, Department of Biomedical Sciences, University of León, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Santos-Lozano
authors.forename: F
authors.initials: F
authors.lastname: Santín-Medeiros
authors.forename: G
authors.initials: G
authors.lastname: Cardon
authors.forename: G
authors.initials: G
authors.lastname: Torres-Luque
authors.forename: R
authors.initials: R
authors.lastname: Bailón
authors.forename: C
authors.initials: C
authors.lastname: Bergmeir
authors.forename: J R
authors.initials: JR
authors.lastname: Ruiz
authors.forename: A
authors.initials: A
authors.lastname: Lucia
authors.forename: N
authors.initials: N
authors.lastname: Garatachea
mesh_terms: D061725:Accelerometry / Q000295:instrumentation / Q000379:methods; D056044:Actigraphy / Q000295:instrumentation / Q000379:methods*; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002153:Calorimetry, Indirect / Q000379:methods; D002648:Child; D004734:Energy Metabolism / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology; D012420:Running / Q000502:physiology*; D016138:Walking / Q000502:physiology*