The present study investigated the effect of a school-based pilot intervention to reduce sedentary time on objectively measured sedentary time, LPA and MVPA. Mean values showed that sedentary time was very high in Belgian school children as they spent more than 60% of their waking time in a sedentary way at the pre-test. At the post-test, this was more than 65%. This confirms that sedentary time is an important target behaviour in health promoting programmes and further efforts are needed to decrease the high amount of sedentary time in children.
Statistical analyses indicated several significant time effects for all outcomes, although the effect sizes were small. In general, there was an increase in sedentary time and decreases in LPA and MVPA for all children. This may best be explained by a seasonal trend and related temperatures, as the pre-test was conducted in September and October and the post-test mostly in December and January. Earlier research in the same age group has demonstrated that temperature is positively related to children’s PA level
] and that the amount of rainfall is negatively associated with PA
] and positively with sedentary time
]. Based on official national weather online services (
), the mean temperature was 16.5° during pre-test weeks and 5.6° during post-test weeks. Moreover, the mean amount of rainfall was 83.1 mm during pre-test weeks and 119.3 mm during post-test weeks. Thus, weather variations between pre- and post-test could have caused the significant time effects on sedentary time, LPA and MVPA, suggesting further research might take the weather influences into account.
Further, no intervention effects were found on the total sedentary time per day, on a weekday, on a weekend day, during school hours, after school hours and on the average length of the sedentary bouts. These results could be attributed to the rather short intervention period. Beside the fact that this was a pilot-test of the intervention, the reason to choose a short intervention period and a rather limited intervention was to make the intervention more feasible to perform, as the actual implementers of the intervention were the teachers, not the researchers, to increase sustainability. In many intervention studies, teachers are asked to implement the intervention in addition to the school curriculum and intervention programmes should therefore be attainable to conduct
]. Also Wahi et al.
] suggested that interventions to reduce sedentary time should be feasibly implemented in fewer sessions over a short period of time. However, a recent meta-analysis
] demonstrated that interventions to reduce sedentary time with an intervention period of less than 4 months yielded small treatment effects. The researchers also stated that sedentary behaviours could have a strong habitual component and are therefore difficult to change, especially in a short intervention period. In sum, the optimal solution is probably to find a compromise between sufficient exposure and practicability for the teachers.
Another possible explanation for the disappointing results is the use of accelerometers to examine the intervention effects in this study. Objective measures provide a good estimate of children’s actual sitting time and are nowadays recommended to measure sedentary time
]. However, because accelerometers do not distinguish between sitting and standing, it is difficult to capture activity breaks. We made the assumption that a shorter length of sedentary bout could reflect more activity breaks (if total sedentary time and the number of bouts are taken into account), but this is a rather arbitrary definition. All this suggests that inclinometers could be a better instrument to disclose intervention effects, and in particular to capture activity breaks.
Finally, the ENERGY-project including the UP4FUN intervention was grounded in a social ecological perspective, highlighting the importance of both individual and environmental factors
]. The focus in this intervention was specifically on parents, but other influencing environmental factors might be taken into account as well when developing an intervention programme to induce an effect on children’s behaviour, particularly since we already stated that sedentary behaviour is a behaviour difficult to change. For example, it could be that involving the community and introducing changes in the physical environment of the school might increase the chance on intervention effectiveness.
It was further hypothesized that children could have replaced sedentary time by LPA, as light physical activities were proposed as an alternative for sedentary activities in the intervention. No significant effect was found, which could be expected as there was no effect on sedentary time as well. We also measured changes in MVPA to examine the possibility that children would have replaced a part of their sedentary time by more intensive activities. A few small statistically significant interaction effects were found, although it was in the advantage of the children in the control schools, who had an increase or a smaller decrease in MVPA in comparison to children of the intervention schools. These results indicate that an intervention specifically aiming at reducing sedentary time, might not have a positive impact on MVPA, confirming that sedentary time and MVPA are two independent behaviours. If researchers want to promote MVPA as well, a multi-component intervention may be needed to reach this goal.
The current study also compared the children in the intervention group who spent less time sedentary at the post-test with the children who spent equally or more time sedentary at the post-test. Overall, not many significant results were found, which means that for most outcomes no specific subgroups could be revealed. Results only showed that children who lived with both parents were less likely to reduce their sedentary time after the intervention than children who did not live with both parents. This is quite surprising as recent research in the same age group found that not living with married/cohabitating parents was associated with an increase in total screen-time over a time period of one year
]. A possible explanation could be that although children lived with both parents, only one of the parents participated actively in the intervention, e.g. reading newsletters, going to the Family Fun Event. It is therefore of importance that both parents are engaged in the intervention. In addition, it was found that children having one or more siblings were less likely to reduce their sedentary time on a weekend day at the post-test than children having no siblings. It could be that children have difficulties in reducing their sedentary time at home, when their siblings are not motivated to reduce their sedentary time as well. This emphasizes the importance of support and modeling of the whole family
]. Further, since girls and the oldest age group were less likely to increase their LPA level at school at the post-test than boys and younger children, teachers implementing the intervention might pay more attention to these subgroups at school. However, it must be kept in mind that these analyses were conducted in a rather small group with an unequal distribution between groups and the results should therefore be cautiously interpreted.
Study limitations included the convenience sample, the use of different accelerometer models and the relatively large drop-out of children due to the lack of valid accelerometer data. Important strengths were the randomized controlled trial with the pre-test post-test design including an intervention and control condition and the involvement of parents.