Sitting or sedentary behavior is associated with several adverse health outcomes such as overweight and obesity, diabetes type 2,... independent of physical activity levels. This evidence is clear in adults, however also in adolescents the health effects can become apparent (e.g. development of overweight, reduced fitness,...). Therefore it is important to develop interventions aiming to reduce sedentary behavior in adolescents. Adolescents are sedentary for more than 60% of the day, of wich a large part is spent at school as during school hours pupils usually have to sit at their desk. Therefore secondary schools serve as an ideal setting to target sitting behavior. Structural environmental changes (in the classroom), e.g. introducing standing desks, can be used as a possible strategy.

It is important to objectively evaluate the effect of the intervention on sedentary behavior. Next to evaluating the effect on behavior, studies also recommend to evaluate the effect on cognitive performance, as this is the particular interest of schools and their staff.

The primary aim of this project is therefore to investigate the effect of implementing standing desks on adolescents' cognitive function, more specifically on memory, reasoning, verbal ability and concentration. In addition, the investigators will evaluate the effect of implementing standing desks on adolescents' sitting and standing time, measured by Axivity accelerometers in the entire sample. Finally, the investigators will also collect information about sleeping behavior to investigate the association with cognitive performance. This will be tested via a controlled trial with a pre- and post-test design including an intervention and control group. Based on previous research studies, the hypothesis is that adolescents from the intervention group will improve their cognitive function and standing time and reduce their sitting time, whereas no changes are expected to be found for adolescents from the control group. Finally, it is expected that a more healthy sleeping behavior is associated with better cognitive performance.

Introduction:

Sedentary behavior is defined as "any waking behavior characterized by an energy expenditure ≤1.5 metabolic equivalents (METs), while in a sitting, reclining or lying posture". Among adults, evidence suggests that prolonged time spent in sedentary behavior is positively associated with type 2 diabetes, cardiovascular diseases, metabolic syndrome and all-cause mortality. Although this association is less consistent among children and adolescents, several studies and reviews have found adverse associations between sedentary time and health outcomes in children and adolescents too. Additionally, a review of reviews has found evidence for an association between screen-time behaviors (i.e. specific sedentary behaviors) and obesity and moderate evidence for an association between screen-time behaviors and blood pressure, total cholesterol, self-esteem, social behavior problems, physical fitness and academic achievement, and these associations are largely independent from moderate- to vigorous physical activity. Moreover, since sedentary time in early life tracks into adulthood where it can have potential health implications, strategies are needed to reduce sedentary time in children and adolescents. Children and adolescents spend more than 60% of the day (waking hours) sedentary. In addition, more than 65% of the time at school is spent in sedentary activities. Therefore, the classroom can be considered an important setting for implementing specific strategies to reduce sedentary time in this target group.

A potential environmental strategy to reduce sedentary time during school hours is replacing traditional desks and chairs with standing desks. Although there is currently no general consensus on the health benefits of implementing standing desks into the classroom, this strategy might have a beneficial impact on children's energy expenditure. For sedentary time, standing time and step counts, results are currently mixed. More research is needed to make strong conclusions, as previous studies often had a low quality design. Furthermore, it is also advocated to focus on secondary schoolchildren, as the majority of studies have been conducted in primary schools and the level of sedentary behavior is high in secondary schools.

However, qualitative data from teachers in secondary schools from a study conducted previously by our research group (see references) indicated that not all teachers are convinced of the added value of implementing standing desks in secondary schools. The major worry is that standing up during lessons might impact pupils' academic performance. As this is a genuine concern, robust evidence that standing desks have positive effects on pupils' cognitive and academic performance is needed to support the introduction of standing desks in schools. It has indeed been advocated to capture such outcomes in further research, as this information is of primary importance for schools. A potential mechanism could be that standing is associated with increased energy expenditure, resulting in an effect on cognitive performance. Currently, two very small studies provide support at the proof of concept level and pilot data that standing desks might impact cognitive function positively among children or adolescents. A pilot study that explored neurocognitive benefits of standing desks in 14-year-olds across secondary schools found that the use of standing desks was associated with significant improvements in executive function and working memory capabilities over a period of about six months. The authors advocated that more research is needed, as the study was conducted in one school with no comparison group and a relatively small study sample (n = 27). Another pilot study investigated the effect of implementing standing desks for 11 weeks into a primary school classroom, and found that the intervention group significantly improved on the Digit Task Span test compared to the control group. No differences were found for the Eriksen flanker task, suggesting that standing desks are more likely to affect the short-term working memory than the inhibitory control. However no firm conclusion can be drawn from this study because its sample size was too small (n = 38) and the intervention period too short. More research is needed to provide a definitive answer.

Finally, in our previous study, only three standing desks per class were installed. The reason to choose three desks was that schools often report the high costs of standing desks as a barrier to implement them. This implied that practicable solutions need to be provided (such as installing a limited amount of desks per class) to broadly promote and disseminate the use of standing desks in schools. In addition, the financial restrictions within the project did not allow the researchers to install a large amount per class. However, this caused that pupils only stood up for 50 minutes per week on average. In the pilot study of Wick et al. who investigated the effect on cognitive function, it was recommended that using the desks for at least 1 hour per school day would be advisable to improve cognitive function. Thus, it will be important for the evaluation to install a sufficient amount of standing desks in every classroom to ensure that adolescents can stand up long enough. In the methodology of this proposal, this will be further specified.

Purpose of the study:

The primary aim of this project is to investigate the effect of implementing standing desks on adolescents' cognitive function, more specifically on memory, reasoning, verbal ability and concentration. In addition, the effect of implementing standing desks on adolescents' sitting and standing time wil be evaluated. Finally, the relationship between sleeping behavior (duration and quality) and cognitive performance will also be investigated. This will be tested via a controlled trial with a pre- and post-test design including an intervention and a control group. Providing evidence on the effect on cognitive functioning of standing desks is the first step, as it could further influence academic performances. As there is currently only preliminary evidence from studies with a small study sample and no control group, this study will definitely be of added value to the research field. In addition, if there would be strong evidence for beneficial effects, this would be a key rationale to introduce standing desks into schools and decisive factor to persuade all teachers (including the more conservative ones) to use standing desks in the classroom.

Study design:

As indicated above, the effect will be tested via a controlled trial including an intervention (3 secondary schools) and control condition (3 secondary schools). A convenience sample for the intervention group and for the control group will be selected in Flanders. The principals will be sent a recruitment letter and afterwards contacted by phone. A priori power analysis, based on a moderate effect size for cognitive function, suggests a total sample size of 90 participants (G*power 3.1.9.2; α = 0.05, 1-β = 0.80). Taking into account a response rate of 80%, the investigators will recruit about 120 adolescents (60 intervention, 60 control) to ensure that 90 participants will complete the measurements. The principals will be asked to select one class per school, with at least 20 pupils per class. In addition, it will be required that the adolescents spend a large amount of time in the same classroom (preferably at least 1/3 of lesson hours, which equals 11 lesson hours per week in the same classroom) in order to be sufficiently exposed to the desks. The investigators will inform the pupils in the classes about our study and provide an information letter for their parents. It will be specified that the standing desks will be delivered to all adolescents from a class (similar as to other health interventions that are delivered by the teacher to the entire class), but that the adolescents are free to participate in the pre- and post-test measurement. All pupils (and their parents) that agree to participate in the measurements, will first participate in the pre-test measurement (February/March 2019). Primary study outcomes will be adolescents' memory, reasoning, verbal ability and concentration (using the Cambridge Brain Science tasks). Major secondary study outcomes will be adolescents' sitting and standing time (measured by the Axivity accelerometer worn during 5 school days) on the one hand and sleep quality (using a questionnaire) and sleep duration (using Fitbits) on the other hand. Afterwards, the standing desks will be implemented for four to five months in the intervention schools (starting immediately after the pre-test). At the end of the school year (June 2019), the post-test will be conducted.*

*Due to the COVID-19 pandemic, the study was interrupted in March (after completion of the pre-test). Therefore, a new pre-test was conducted (in a new sample) in September/October 2020, which was followed by the exposure to the standing desks for approximately 4 or 5 weeks. In November/December 2020 the post-test was conducted.

Implementation of the standing desks:

To ensure that adolescents will spend sufficient time at the standing desks, 1/3 to half of the classroom will be provided with standing desks. The school will be asked to actually replace some traditional desks with these standing desks, instead of just adding standing desks to the classroom set-up to ensure as much as possible that the desks are being continuously used throughout the intervention period. Prior to installing the standing desks in the classrooms, a training session will be delivered to the teachers about the importance of using standing desks in terms of health promotion and how the teachers can motivate the pupils to use standing desks, and how the standing desks need to be safely and appropriately used. In addition, a rotation system will be suggested in which adolescents rotate every lesson hour, based on the findings and suggestions from our previous study. Further, a poster with a motivational quote will be provided to hang on the wall to remind and motivate pupils and teachers to use the desks. Finally, every month a researcher will go to the intervention class to evaluate if the standing desks are frequently used and if there are any difficulties and to encourage everyone to keep using the desks (also by providing a new poster every time). These strategies will be important, as it was found in our previous standing desk study that the use of standing desks decreased over time, probably because introducing standing desks can have a novelty effect.

Statistical analyses:

To evaluate the effect of the standing desks, Repeated Measures MANOVA will be executed with time as a within-subjects factor (pre- versus post-test) and condition as a between-subjects factor (intervention vs. control group), using MLwiN 2.31 (Centre for Multilevel Modelling, University of Bristol, UK) to take clustering of adolescents in schools into account.

Inclusion Criteria:

• A 7th or 8th Grade class
• General secondary education
• Spending at least 11 lessons hours per week in one classroom

Exclusion Criteria:

• Technical or vocational secondary education

All IPD that underlie results in a publication.

Will be published together with publication of the article(s).

Dependent on journal: Probably depositing into data repositories or by publishing the data and files as supplementary information in the journal.