Several studies with objectively measured sedentary data have shown that the number of hours of sedentary time is related to metabolic risk factors (13, 14, 21).
Patterns of sedentary behaviour will be assessed by power law analyses of the lengths of sedentary bouts fitted from raw sedentary data.
17 While it is not ideal to include standing as a measure of ST, it is often necessitated by the unavailability of sitting-specific data, and standing is routinely included in objectively measured sedentary data as accelerometers are unable to differentiate between time spent sitting or standing.
Although OPAL participants spent on average 11 h per day sedentary, our data showed no associations for sedentary time.
The physical activity and sedentary behavior data were collected four times per year, thereby providing an estimate of true activity levels independent of the effects of seasonality.
The study forms the NZ arm of the international IPEN-Adolescents collaboration, whereby adolescents' physical activity and sedentary behavior data are collected using a common methodology across multiple countries.
This study will contribute to national and international scientific knowledge by forming the NZ arm of the international IPEN-adolescents collaboration, whereby adolescents' physical activity and sedentary behaviour data are collected using a common methodology across multiple countries (Australia, Belgium, Brazil, China, Denmark, Malaysia, New Zealand, Portugal and the USA).
The Gruve device is a waist worn accelerometer which monitors sedentary time and data are downloaded easily to the interactive Gruve website.
In future work we will determine the criterion validity of the SIT-Q by comparing estimates of sedentary behavior against data collected using the activPAL® inclinometer (PAL Technologies, Glasgow, Scotland).
The strengths of this study include the large UK-wide and representative sample, the use of accelerometers to provide objective measures of PA and sedentary time, and the data processing undertaken to exclude any data that might be unreliable.
In addition, a re-analysis of the data modeling sedentary time as the mediator and waist circumference as the outcome showed that, although significant, sedentary time attenuated the effect of birth weight on waist circumference by only 2% (compared with 32% when waist circumference was the mediator; data not shown), which supported the use of waist circumference as a mediator in our analyses.
