Changing children’s lifestyle habits from sedentary to physically active may be an important step to prevent, reverse and/or manage obesity. The increased use of technology has caused children to sit for long periods of time. This is of great concern as sitting may have detrimental health effects into adulthood independent of lack of physical activity. This thesis represents a series of studies designed to better understand sedentary behaviour in children. Firstly, it was important to establish the validity of a monitor that differentiated sitting from standing in children in both laboratory and school settings. In this thesis, the ActivPAL monitor was used which had not been validated in children previously. Secondly, a pilot observational study was conducted in a primary school to identify the period where children were most sedentary. Thirdly, it was important to determine the most appropriate and feasible strategies by interviewing teachers and principals, before intervening in a classroom environment. Fourthly, a “dynamic classroom” which encouraged less sitting, and more standing and movement in children was implemented in one primary school.

In Study 1 (Chapter 2), the validity of the ActivPAL monitor in measuring sedentary behaviour of primary school children in a laboratory setting was objectively examined against video observation and other known motion sensors. A strong correlation (r ≥ 0.99) was found between the video recordings and the ActivPAL data in time spent sitting/lying, standing, stepping, and sit to stand and stand-to-sit transitions, and step counts in slow and normal walking but not in fast walking and running.

In Study 2 (Chapter 3), the validity of the ActivPAL monitor in assessing free-living sitting/lying, standing, and stepping time, and transition and step counts in children was examined at school compared to direct observation. There was a strong correlation (r = 0.77-0.99) between the video and the ActivPAL in measuring sitting/lying, standing and stepping time, and step counts in both classtime and unstructured play. In counting classtime and playtime stand-to-sit transitions, correlation (r = 0.53-0.61) was moderate. The results of Studies 1 and 2 showed that the ActivPAL monitor was overall a valid device in measuring sedentary behaviour in children in both laboratory and primary school settings.

In Study 3 (Chapter 4), the time children spent sitting, standing and stepping, in a typical school day, was quantified by the ActivPAL monitor. Children spent 56% sitting, 25% standing, and 18% stepping during a school day, however, 49% of sitting occurred in classroom. These findings suggested that an intervention to reduce sitting time in the classroom was needed.

In Study 4 (Chapter 5), the most appropriate and feasible strategies to reduce children’s sitting time in the classroom were identified by interviewing primary school teachers and principals. It was found that height-adjustable standing desks/workstations and Swiss balls could be incorporated in the classroom.

The effectiveness of a “dynamic classroom” environment in reducing children’s sitting and increasing standing was tested in Study 5 (Chapter 6). Traditional desks and chairs from a classroom were completely removed and height-adjustable standing workstations, Swiss balls, bean-bags, and benches were incorporated in the classroom over two school terms (22 weeks). Children’s sitting and standing were objectively measured using the ActivPAL monitor at three time points (baseline, week 5, and week 9). Pain, inattention and hyperactivity were also assessed at baseline, midline, and the final time point. At week 22, an interview with the intervention class teacher and a focus group with children were conducted. During school, there was a large increase in standing (intervention: 2.06 (0.44), mean (SD); control: 1.60 (0.69) h/day) which persisted across the full day (3.71 (0.92); 2.77 (0.76) h/day). Children and school staff were supportive of the “dynamic classroom” intervention as it offered increased space, social interactions, happier children, and better, quicker and easier supervision. The “dynamic classroom” seemed to increase concentration specifically in children with Attention Deficit Hyperactivity Disorder (ADHD). Height adjustable standing workstations were successfully integrated into the classroom environment to increase standing and decrease sedentary time in children.

In conclusion, the school environment, where children spend most of their time, may be an effective setting to reduce sitting time in children. It seemed that incorporating height-adjustable standing workstations in the classroom to be a feasible and inexpensive strategy to encourage children to stand more and sit less. Future studies should investigate the impact of the “dynamic classroom” intervention on a larger sample for a longer period.