Gt3x monitor

Participants’ height was measured barefoot to the nearest 0.1 cm using a portable stadiometer (Seca Stadiometre, Seca Ltd., Birmingham, UK), and weight was measured barefoot with light clothing to the nearest 0.1 kg on electronic scales (Seca Digital Scales, Seca Ltd.). From measured stature and body mass, a BMI z-score was calculated relative to the UK 1990 BMI population reference data.³⁹ (link) Thereafter, all participants wore 1 ActiGraph GT3X+ monitor on their nondominant wrist for 7 days. Verbal confirmation of each participant's nondominant wrist was noted, and device placement was demonstrated. All participants were fitted with their device before leaving the testing session. Before testing, each accelerometer was synchronized with Greenwich Mean Time and initialized to capture data at 80 Hz. Each accelerometer was programmed to commence data collection at 06:00 on the day after participants received the devices. The low-frequency extension was not enabled. Participants were instructed to wear the device at all times (i.e., 24 h/day) for 7 days, except during any water-based activities such as swimming or bathing. Because poor compliance and subsequent selection bias and misclassification is often cited as a limitation of hip-worn accelerometer studies,³⁶ (link) we used the 24-h wear time protocol to encourage compliance.

Accelerometry data were collected on all children and parents at baseline and 36 months using the ActiGraph GT3X + monitor. Participants were instructed to wear the monitor on the right hip for seven complete days, including during sleeping and water activity (e.g., bathing, swimming, showering). Wear-time criteria were developed by NIH’s Childhood Obesity Prevention and Treatment Research Consortium and were 4 days (3 weekdays and 1 weekend day) of at least 6 h of activity 05:00–23:59. Before physical activity variables (including wear time and valid wear days) were derived, a previously validated algorithm was applied to remove nonwear time based on specific patterns of consecutive zero counts (Choi et al., 2011 (link), Choi et al., 2012 (link)). The cut-points that categorized child movement into minutes of SRT and MVPA were based on previously validated algorithms for preschoolers (Butte et al., 2014 (link)). Percentage MVPA or SRT were computed by dividing mean daily minutes of MVPA or SRT by the total mean daily wear time.

We used an ActiGraph GT3X monitor (ActiGraph, Pensacola, FL, USA) to assess the PA. The GT3X is a small and light monitor device that provides activity counts as the outcome measure of PA. Larger counts stand for the higher level of activity. This is a reliable and valid instrument based on previous data from healthy populations.²³ (link) The accelerometer monitor was placed on the right hip using an elastic belt for 1 week.²⁴ (link) Caregivers and teachers were asked to record the times that children woke up, wore the ActiGraph on/off and went to bed on a 7-day time sheet. The accelerometery data collected from waking hours were employed to analysis using the ActiLife™ software (ActiGraph). Based on previous studies, the accelerometers were programmed to collect data in 1 min intervals and the output was expressed based on vector magnitude (VM) score as counts per minute (cpm) or overall PA.²⁵ Other variables were provided by dividing the overall PA into 2 categories based on day-time, in-school (08:00–14:00) and after-school (16:00 to bedtime), seeking to examine time–activity patterns. To control for school's finish time, a 2 h gap between 14:00 and 16:00 was considered.