GMS 15 yr

Background and participants
In many parts of the world policy and research interventions to modify sedentary behavior of children and adolescents are now being developed. However, the evidence to inform these interventions is limited. This data was collected to assess levels of sedentary behavior and physical activity in 14-16y old adolescents. Participants were part of the Gateshead Millennium Study cohort. Physical activity and sedentary behaviour measures were collected when participants were 14y to 16y old (September 2014 to September 2015). Data in the file has been anonymized. The study was approved by the Newcastle University Faculty of Medical Sciences Ethics Committee.

Measurements
Sedentary behavior and physical activity were measured using an ActiGraph GT1M accelerometer (ActiGraph Corporation; Pensacola USA). Participants were asked to wear the accelerometer on the right hip during waking hours for 7 days. Participants recorded the times when the monitor was put on in the morning, taken off at night and any additional periods the monitor had to be removed (e.g. for a bath). Non-wear time/sleep data were removed manually based on the wear time diaries and visual inspection by a trained researcher before data analyses. Data were collected in 15-second epochs and included in the analyses if participants had at least three days with 6 hours per day of accelerometry data. Epochs were defined as sedentary when recorded counts were ≤25 counts/15 seconds, light physical activity >25 counts/15 seconds – 800 counts/15 seconds, moderate physical activity >800 counts/15 seconds – 2050 counts per 15 seconds and vigorous physical activity >2050 counts/15 seconds.

Outcomes
A custom Microsoft Excel macro was used to calculate time per day spent in each of the physical activity intensities and the percentage of time per day. To assess sedentary fragmentation the average duration of a break and total number of breaks/hour were calculated. A break was defined as any period of time ≥1 min of consecutive counts >25 counts/15 seconds (this would equate to for example 1 minute of slow walking). In addition, fragmentation of sedentary behavior was also assessed by calculating the number of sedentary bouts per hour of sedentary time and the number of sedentary bouts lasting 1-4 min, 5-9 min, 10-14 min, 15-29 min and ≥30 min. Last, the duration of bouts making up for 50% of total sedentary time was calculated.

Dataset
The dataset is in an excel format and contains secondary data. Each row is an individual participant. Descriptions of the variables and coding can be found in the readme file and in the excel file on the Variable explanation sheet.