Sit-stand desks to reduce sedentary behaviour in 9- to 10-year-olds: the Stand Out in Class pilot cluster RCT

Sedentary behaviour, physical activity and health in children

Childhood is a critical period for the establishment of healthy lifestyle behaviours, including physical activity. Continual advances in modern technology, economic progress and changes to our environments have resulted in reductions in physical activities associated with daily living, and in sedentary behaviour becoming ubiquitous within all settings of daily life. Sedentary behaviour is a behaviour distinct from physical (in)activity and is currently defined as ‘any waking behaviour characterised by an energy expenditure of ≤ 1.5 metabolic equivalents (METs) while in a sitting, reclining or lying posture’. 1 Although reclining and lying postures are included in the definition, most of the time an individual (young people and adults) spends sedentary will be in a sitting position during waking hours. Participation in regular physical activity has numerous short- and longer-term physiological, psychological and social benefits for young people. 2–4 For example, reviews have shown that physical activity can improve blood pressure, weight status and bone mineral density, and lead to improvements in self-esteem and depression, and, in the longer term, can prevent chronic disease. 2,4 It is acknowledged that physical activity is beneficial to health, and sedentary behaviour has been shown to adversely affect health.

Sedentary time is associated with an increased risk of metabolic syndrome,5 cardiovascular disease,6–8 type 2 diabetes mellitus,7,8 all-cause mortality9 and depression10 in adults. Although the evidence for associations between objectively assessed sedentary time and health outcomes in young people is less consistent,11–13 the proxy sedentary behaviours of television viewing and screen time (the most prolific area of sedentary behaviour research) are unfavourably associated with body composition, fitness, self-esteem, cognitive development, pro-social behaviour, academic achievement in children13,14 and cholesterol in adulthood. 15 Sedentary behaviours in children have, furthermore, been shown to coexist with lower levels of physical activity16 and other ‘unhealthy’ behaviours, such as increased consumption of energy-dense foods, lower intakes of fruits and vegetables,17 and inadequate sleep. 18 Furthermore, recent evidence suggests an association between sedentary behaviour and several markers of inflammation and endothelial dysfunction,19 signalling potential mechanistic links with poor cardiovascular health in children. In addition, the emergence of an increased cardiometabolic health risk profile in some population groups is evident during the first decade of life. 20 For example, British South Asian children have demonstrated higher levels of glycated haemoglobin, fasting insulin and triglycerides, and lower high-density lipoprotein cholesterol than white British children, as well as having a higher sum of all skinfolds and fat mass percentage. 21,22 Therefore, these populations may be more vulnerable to the adverse affects of excessive sedentary time. Indeed, evidence of the influence of sedentary behaviour on the health of young people has prompted many countries to establish public health recommendations for sedentary behaviour. The UK, USA, Canada, Australia and the Netherlands, for example, now recommend that young people should reduce sitting time and break up long periods of sitting as frequently as possible. 23–27

Prevalence of sedentary behaviour in children

In the UK, sitting is the most prevalent behaviour exhibited during waking hours in children, accounting for > 65% of their waking time (or 7.5 hours),28 with some children reportedly sitting for > 10 hours per day (> 70% of waking hours). 29 Accelerometer data from the Health Survey for England have shown that young people (aged 5–15 years) spend, on average, 7 hours per day sedentary. 30 International research shows similar prevalence rates, with data from the International Study of Childhood Obesity, Lifestyle and the Environment (ISCOLE)31 showing that children across 12 geographically and culturally diverse countries spend an average of 8.6 hours per day sedentary. 31 Similar proportions of waking hours spent sedentary have also been reported in children and adolescents from Canada and the USA. 32,33

Objective (accelerometry) sedentary behaviour data further suggest that children spend the majority of their school time sedentary. 34,35 For example, in children aged 10–12 years, across five European countries, 65% of the time spent at school was sedentary. 35 More recently, research has turned to inclinometer devices to more accurately measure total sedentary time (or sitting specifically), with data from these devices from British, Australian and Malaysian children (aged 8–12 years) further confirming that the majority of their time at school (70–71%), on weekdays (53–69%) and weekend days (60–73%) is spent sitting. 29,36–38

The rising prevalence of sedentary behaviour (and sitting) is of further public health concern because this behaviour in childhood has been shown to increase across key transitions in children’s lives (i.e. from primary to secondary school),39 and has been shown to track into adolescence40 and adulthood. 15 Given the physiological and psychosocial risks related to sedentary behaviour, and the evidence that sedentary behaviour increases as children get older, there is a need for interventions to reduce sedentary behaviour and increase movement in children.

Interventions to reduce sedentary behaviour in young people

The environments and social norms that children are exposed to have dominant influences on their activity behaviour. Given that children spend half of their waking hours at school, it is plausible that the school environment may be a critical influence on their health behaviour patterns41–43 and be a most appropriate target environment for interventions. A plethora of physical activity interventions aimed at young people have been conducted over the past two decades. 44,45 School-based interventions promoting physical activity have been successfully implemented during physical education classes, break times and before and after school hours, and have revealed positive effects on physical activity. 44 Furthermore, there is now growing evidence supporting the use of physical activity as a teaching tool (e.g. physically active learning) and classroom movement breaks, as a means of facilitating classroom management, student attention and focus on task. 46 However, teachers, education departments and organisations frequently cite a crowded curriculum, alongside other barriers, such as lack of knowledge or confidence, as reasons for not implementing physical activity programmes. Thus, alternative methods that do not add to teachers’ workload and require minimal specialist knowledge are required.

With an increasing interest in sedentary behaviour, a number of systematic reviews and meta-analyses have been published, synthesising the interventions that focus on young people. 47,48 Although most interventions specifically targeting sedentary behaviour have been home or school based, sedentary behaviour has typically been targeted as screen time and via behaviour change strategies within non-school settings (i.e. screen time at home),48 the effects of which have been inconclusive. 47 Most interventions specifically targeting sedentary behaviour have not been based on a behaviour change framework or theory. 48 In a recent review of interventions targeting sedentary behaviour, only 10 out of 21 interventions included studies that were theory based. 48 Theoretical frameworks provide a scaffold for intervention development from being an evidence-based source for understanding the behaviour of interest and possible levers of change,49 allowing a systematic evaluation of the intervention outcomes. Theories and frameworks typically utilised in sedentary behaviour interventions to date, again which have largely targeted screen time, include social cognitive theory, behavioural choice theory, the social ecological model and the chronic care model. 48

Although there is an abundance of behaviour change theories, models and frameworks for researchers to use (indeed 83 were identified in a recent systematic review49), the behaviour change wheel (BCW)50 has increasingly received attention within the sedentary behaviour literature. 51,52 The BCW synthesises 19 pre-existing frameworks of behaviour change into a single interface, incorporating a theory of behaviour, intervention functions and associated policy categories, and can be applied to any behaviour in any setting. 50 As policy can only influence behaviour through interventions, which in turn act through capability, opportunity and motivation, the framework is represented as a wheel with an outer layer (policy categories) influencing the next layer (intervention functions), until behaviour is changed at the very centre of the wheel. 50

The capability, opportunity, motivation – behaviour model (COM-B) (sources of behaviour) hypothesises that for specific behaviours to occur, the individual must have both the physical and psychological capability to perform the given behaviour, along with the social and physical opportunity to perform the behaviour, and be motivated to perform the specific behaviour more so than any other behaviours within that moment in time. Within the context of sedentary behaviour, the only interventions that have consistently demonstrated a reduction in sedentary time in younger populations are those utilising a standing desks design within the classroom (i.e. environmental restructuring),53 thus providing a physical opportunity for children to stand and/or break up their sitting time. As children spend up to 6 hours per day in the school environment and owing to the potential reach of school-based interventions to tackle inequalities (i.e. demographic and social/cultural), changing the traditional classroom environment to an activity-permissive one by reducing sitting in this environment (rather than the traditional focus on leisure time screen use) is a promising area of research. Indeed, environmental restructuring to provide a physical opportunity to stand rather than sit would certainly be essential within the classroom environment, as traditional furniture dictates that children spend most of their class time sitting. However, implementing new practices and/or changing existing practices in organisations, such as schools, require changes in individual behaviour (i.e. pupil) and collective behaviour (i.e. teachers/school staff and pupils), and changing behaviour requires an understanding of the influences on behaviour in the context in which they occur. Our understanding of these factors can be enhanced through the theoretical domains framework,54 which provides a theoretical lens through which to view the cognitive, affective, social and environmental influences on behaviour. 55

Interventions to reduce sitting within the classroom environment

There are now a growing number of environmental interventions that aim to reduce classroom sitting time and increase standing and movement, which have been implemented in schools and evaluated for effectiveness through systematic reviews. 56,57 Feasibility studies, including our own,29,58,59 have demonstrated the effectiveness of incorporating sit–stand desks in primary school classrooms over the short term (< 12 weeks). For example, sit–stand desks have been shown to enable pupils to alternate between sitting and standing without disruption to teaching, learning or behaviour. 56 Furthermore, sit–stand desks in classrooms have been shown to be effective in increasing energy expenditure60,61 and standing and movement62 during the school day. In addition, studies have shown that sit–stand desks in classrooms lead to improvements in children’s posture and musculoskeletal comfort,63,64 levels of academic engagement65 and achievement,64 and improved cognitive function. 66 Sitting time has been shown to be reduced by between 44 and 60 minutes per day and standing time increased by between 18 and 55 minutes per day during classroom time at school, over 4 and 9 weeks’ follow-up. 29,59,67 More recently, the impact of standing desks on sitting time in the classroom has been assessed over 16 weeks’ follow-up, with results suggesting a 13% reduction in sitting and a 31% increase in standing at school, relative to baseline. 68 Clearly, incorporating standing desks in classrooms shows great promise for reducing children’s sitting time. However, systematic reviews have concluded that the majority of studies conducted to date have included relatively small samples, have been short in duration, have not included a randomised controlled design and have not assessed the impact of standing desks on academic performance. 56,57,69 Further exploration in this area of research is thus warranted.

Development of the Stand Out in Class study

The feasibility of incorporating sit–stand desks in the classroom environment over a 9-week period was demonstrated in an earlier intervention study we conducted with Year 5 Bradford primary school children. 29 In this feasibility study, we verified a number of our outcome measures (objectively determined sitting time and physical activity, body composition, blood pressure and teacher-reported pupil behaviour). In a novel approach, we replaced three standard desks (sitting six children) with six sit–stand desks. The teacher rotated the children assigned to the intervention group around the classroom in groups of six, according to the lesson being taught, using naturally occurring breaks between lessons to do so, ensuring that each child was exposed to the sit–stand desks once a day for at least 1 hour. Children in the control group continued with their usual practice, with no environmental changes to their classroom. Reductions in classroom sitting of 52 minutes per day were observed within the intervention group and reductions in total daily sitting of 81 minutes per day on school days after 9 weeks were seen. Teachers reported improvements in behaviour and no perceived negative effects on teaching or learning were observed. As part of this feasibility work, we also compared the changes in classroom sitting observed in our sample with data from a related feasibility study conducted in a primary school in Melbourne, Australia. 29 In the Melbourne study,29 every child in the intervention classroom had a sit–stand desk. Despite differences in desk provision, no significant differences in reductions in sitting time were observed between the two studies. Reductions in classroom sitting of 44 minutes per day and reductions in total daily sitting of 68 minutes per day were observed in the Melbourne intervention class. This early work demonstrates the potential of sit–stand desks in the classroom as a way of reducing sitting in children over the short term, irrespective of the type of sit–stand desk provision.

Following this successful feasibility work, the next logical step required was the development of the Stand Out in Class intervention. With the aim of informing a future definitive trial, the Stand Out in Class pilot study was developed to establish procedures for school and participant recruitment, and the acceptability of the intervention and outcome measures, and attrition rates. This intervention was informed by our feasibility work and public and patient involvement (PPI) with teachers and children through informal interviews and workshops (children only), in which our earlier work was described and their feedback on the intervention and proposed measures was obtained. This present study therefore comprises a pilot evaluation of the implementation of standing desks in the classroom through a cluster randomised controlled trial (RCT), with objective measures of sitting and activity, and a range of health- and education-related outcome measures. Rapid increases in sedentary time have been observed in children aged ≥ 11 years, relative to younger age groups. 70 This study targets Year 5 classrooms, comprising children just below this age (9- to 10-year-olds), with the goal of reducing the typical rise in sedentary time seen during the transition into adolescence,39 given also that sedentary behaviours track from childhood into adolescence and adulthood. 40 Furthermore, evidence suggests that children in Year 5 upwards are active participants in their own learning, making them an optimal target for classroom interventions that may facilitate learning. 71 A cluster design is considered appropriate because the intervention is delivered at the classroom level, rather than at an individual level.

Pilot trial study objectives

1. Establish and refine a recruitment strategy for schools and pupils.

2. Determine attrition in the trial (schools and children).

3. Determine completion rates for outcome measures (and whether or not these are sufficiently high to provide accurate data in a full trial).

4. Assess whether or not there are any differences in trial recruitment, retention and acceptability between ethnic groups.

5. Assess the acceptability of randomisation to schools.

6. Assess the acceptability of measurement instruments to teachers, children and parents, including the activPAL™ (PAL Technologies Ltd, Glasgow, UK) inclinometer, as the tool for the measurement of the primary outcome.

7. Assess the acceptability of the intervention to teachers, children and parents.

8. Monitor any adverse effects, such as musculoskeletal discomfort and/or disruption to the classroom/learning, to inform the design of a full trial and minimise or eliminate any such effects.

9. Assess intervention fidelity.

10. Derive preliminary estimates of the effect of the intervention on children’s total daily sitting time, physical activity, indicators of health (markers of adiposity and blood pressure), cognitive function, and academic performance, engagement and behaviour.

11. Estimate the standard deviation (SD) of the primary outcome to inform a sample size calculation for a full RCT.

12. Determine the availability and completeness of economic data, and conduct a preliminary assessment of potential cost-effectiveness.

Trial feasibility-related outcomes

The primary aim of this pilot study was to establish school and participant recruitment and retention rates, the acceptability of the intervention and proposed outcome measures, intervention and measurement fidelity, and the availability and completeness of economic data for an estimation of potential cost-effectiveness, to inform the development of a definitive trial. Study uptake was monitored by recording the number of schools and pupils approached, and the number agreeing to participate (objective 1). Withdrawal rates of schools and children (objective 2) and completion rates for outcome measures were recorded (objective 3), and these feasibility outcomes were compared between ethnic groups (objective 4).

Process evaluation

A series of interviews and focus groups with teachers, children and parents were conducted following the completion of the baseline measures and randomisation to explore the acceptability of the trial procedures, including randomisation (objective 5), and the acceptability of the measurement instruments (objective 6). The acceptability of the intervention (objective 7) and children’s, teachers’ and parents’ perceptions and experiences of the intervention and outcome measures were determined during the intervention through a further set of interviews (n = 4 with teachers from the intervention schools) and focus groups (n = 4 with children from the intervention schools) (objective 8). Potential differences in the trial and intervention acceptability between ethnic groups were explored as part of the analyses from the focus groups (objective 4). Towards the end of the intervention, four one-to-one interviews were also conducted (one per intervention school) with senior staff (head teachers/deputy head teachers) to further examine the acceptability of the intervention (objective 7).

To assess intervention fidelity, intervention classrooms were observed by a member of the research team for the duration of at least half a school day during the spring and summer terms. Field notes were taken to document the occurrence of any intervention components (i.e. use of prompt cards, engagement with a standing champion; see Table 1) during the observation period. In addition, children’s postures during sit–stand desk use were recorded using a postural analysis recording system based on the portable ergonomic observation63 to assess any potential future risk of musculoskeletal injury (objectives 8 and 9). Full details of the process evaluation methods, analyses and results are described in Chapter 5.

Health- and education-related outcome measures

All health-related outcome measurements were taken twice: at baseline prior to randomisation and approximately 7 months after baseline when pupils were at the end of Year 5 (the sit–stand desks remained in the intervention classes until the end of Year 5, while the follow-up measures were taking place).

Primary outcome for a subsequent definitive trial

The proposed primary outcome for a future definitive trial is change in mean daily sitting time on weekdays (school days). Mean daily sitting time on weekdays was chosen, given that the intervention was school based. Sitting time measured across the whole school day/weekday was proposed, as this measure encompasses school hours and out-of-school hours and factors in any compensatory effects of the intervention, should any beneficial effects of the intervention experienced during school hours be cancelled out by an increase in sitting after school, for example. Table 4 displays the descriptive statistics for all activPAL variables recorded throughout waking hours on weekdays for the control and intervention groups.

A weighted linear regression model was calculated to compare the primary outcome for the subsequent definitive trial (change in average weekday sitting time between baseline and 7 months’ follow-up) between pupils in the control group and those in the intervention group. The model was weighted by the number of participants followed up in each cluster (sum of weight = 110 observations). The model was adjusted for baseline average weekday sitting time for each cluster and for average weekday wear time when awake across the two time points (baseline and 7 months). Owing to the exploratory nature of the trial, the results are presented as weighted mean differences with 95% CIs. As the variables in the regression model reflect cluster means rather than individual observations, analytically weighted least squares was the method of estimation used, in which cluster sizes were the weights.

The model revealed that children in the intervention group spent less time sitting than children in the control group. The mean difference (weighted by school size) in change in sitting time (in minutes) adjusted as described above was –30.6 minutes per day (95% CI –56.42 to –4.83 minutes per day).

The addition of baseline season of activPAL data collection to the weighted linear regression model did not affect the difference in sitting time between groups. When follow-up season was included in the model, the adjusted difference in sitting time between groups was –26.64 minutes per day (95% CI –73.08 to 19.79 minutes per day).

Sensitivity analyses of the proposed primary outcome in a definitive trial

Owing to the exploratory nature of this pilot study, participants were included in the preliminary analyses presented in Primary outcome for a subsequent definitive trial if they wore the activPAL for a minimum of 8 hours on at least 1 weekday. To assess whether or not the number of valid days of activPAL wear had an effect on the estimates (to inform wear time criteria in a definitive trial), the preliminary primary outcome analysis described in Primary outcome for a subsequent definitive trial was rerun to include only those participants with specific days of valid activPAL data. These results are presented in Table 5. Similar differences to those described in Primary outcome for a subsequent definitive trial between groups were observed for participants providing at least 2 and 3 valid days of wear; however, these differences appear to be attenuated when considering only participants with at least 4 valid days of activPAL data.

Secondary outcomes for a subsequent definitive trial

Health markers (adiposity and blood pressure)

Table 11 displays the descriptive statistics for the anthropometric and blood pressure measurements taken from participants at baseline and follow-up. The changes seen in the anthropometric measurements over the follow-up period are reflective of typical growth-related changes in children of this age.

Cognitive function

Cognitive function was assessed using three separate tests: the Stroop test, the Corsi block-tapping test and the RVIP test. The outcomes derived from these measures are summarised in Table 12. Overall improvements in the performance on most test components were observed in both groups over the follow-up period, probably due to a learning effect of these tests.

Musculoskeletal comfort

Table 13 presents results from the child-reported Body Comfort Survey (summarised scales), which shows the proportion of pupils who feel good at their desks. At the 7-month follow-up, there was an increase in the proportion of pupils from both groups who reported that they felt better at their desk.

Classroom disruption and pupil behaviour

Pupil behaviour, conduct in the classroom and interactions with fellow pupils were examined using the teacher-reported Strengths and Difficulties Questionnaire. Descriptive statistics for this measure for the control and intervention groups at baseline and follow-up, along with the changes in ratings, are summarised in Table 14. The lower the score in each subscale, and the lower the total score, the better the behaviour. The intervention group generally had reduced antisocial and hyperactive behaviours and increased self-control compared with the control group at follow-up.

Engagement and disaffection with learning

Participants self-reported their engagement and disaffection with their own learning using the Engagement Versus Disaffection with Learning Questionnaire. Table 15 summarises the scores for each subscale of this measurement tool at baseline and at follow-up, along with the changes in scores calculated over the follow-up period. There were no noticeable between-group differences in the mean change in any subscale score over the trial period.

Academic progress and attainment

An overview of the results for school performance per class is shown in Appendix 2, Table 26. Table 16 shows the combined data from which the comparisons were made. There were no differences between change in expectation level for maths and writing between the control and intervention groups. However, fewer participants in the intervention group (n = 4) than in the control group (n = 16) experienced a decrease in reading expectation.

Data sources

Missing data

Missing data are a concern in cost-effectiveness analysis because costs or health outcomes in individuals with missing data may be systematically different from those with fully observed information. Inappropriate missing data strategies have the potential to bias resource allocation decisions. 124 We followed a recent presentation framework in setting out our missing data strategy below (see Missing data strategy). 125

Methods

Results

Table 17 summarises resource use categorisation and corresponding reference costs, per resource use, collected from PSSRU121 and NHS Reference Costs 2015–16. 122 For survey items for which a recent reference cost had not been calculated, a close comparator was used for costing. This was applicable for only one resource item, where the survey item ‘other counsellor/therapist’ was assumed to be comparable to the cost of a GP counsellor. Estimating the cost of some other resource items required further assumptions, such as resource items requiring home visits, which involved assumption of the amount and cost of travel time. Assumptions, when made, were kept consistent between closely comparable resource items. Full details of the assumptions for each item are presented in Report Supplementary Material 2 alongside their source.

Recent reference costs were readily available for survey items with the highest reported use, such as GP surgery visits. In less frequently utilised services, costs were less readily available in the literature. For this reason, given relatively low reported use, the impact of assumptions to approximate health-care resource costs in categories where these costs were not directly available is expected to be minimal. Inpatient stays were costed as an average of hospital costs per day, rather than by individual Healthcare Resource Group coding for any procedure named in complete cases. This was expected to limit unexplainable variation in imputed hospital costs due to different Healthcare Resource Group costs of conditions treated in each arm by inpatient stay recorded in complete cases.

Costs are presented in 2016 Great British pounds. When cost estimates were gathered from historical sources, they were inflated to 2016 prices using the Hospital and Community Health Service Index reported by the PSSRU. 121 Total resource costs and outcomes in health and education are presented in Table 18.

The number of health-care contacts in complete cases in each trial arm appears to vary. This is largely driven by a small number of high-use patients. In the control arm at follow-up, 11 of 15 instances of ‘psychological care’ are for one pupil who reported weekly counselling appointments. Similarly, in the intervention arm at follow-up, 15 of 17 ‘hospital care’ contacts were for a pupil who received surgery for a burst appendix and therefore required an extended inpatient stay.

In the full base-case cohort, mean costs of hospital care in the intervention arm appear large; however, this was, in part, driven by the previously described surgery for one pupil, costed at £5836.50. Overall, there appears to be little interpretable difference in estimated health-care costs in the prior 3 months between trial arms. The mean cost of the intervention per pupil was comparatively small, and if costed over the same 3-month time horizon, rather than a full year, the mean cost of the intervention during the trial period reduces from £7.58 to £1.90 per pupil.

Education resource use across all categories appears slightly higher in the intervention group than in the control group at follow-up. However, when baseline patterns of resource use are considered, the level of education resource use in the intervention arm appears stable between the two time points, whereas resource use increases in the control arm between summer and winter. Education outcomes collected are, however, difficult to interpret. For example, interpretation of an increase in pupils receiving additional tutoring in the control arm between time points is highly context dependent. This could be due to a change in teaching style within the school, or by revision of expectations by parents. Again, there appears to be little interpretable evidence of divergence in resource use between the intervention and control arms during the trial period that could be attributed to the intervention.

Comparing EQ-5D-Y profiles at follow-up suggests that health outcomes also diverge little between groups. The largest difference was a 6% difference in report of pupils experiencing some pain and discomfort, with a higher number reporting ‘no problems’ in the intervention arm. This corresponds roughly to a difference of five pupils. There were, however, 4% more pupils reporting some anxiety in the intervention arm than in the control arm and a similar 4% increase in reported problems in self-care in the same group.

When assessing EQ-5D-Y profiles between the two time points, a more significant trend emerges of changes in the characteristics of reported health profiles between baseline and follow-up. In both trial arms, the percentage of pupils reporting ‘no difficulties’ in mobility, self-care and pain/discomfort decreases between baseline and follow-up, meaning a higher number of pupils report at least some difficulties in these dimensions. Both trial arms report an increase in mobility problems between baseline and follow-up, a change of 6% in the control arm and 8% in the intervention arm.

The EQ-5D-Y profiles reveal some further divergence between trial arms. Although in the control arm there is an 11% increase in the number of pupils reporting at least some pain, in the intervention arm there is an increase in reported pain of only 1% between time points. In the ‘usual activities’ dimension, there is a 4% increase in reported problems in the intervention group between time points, whereas there is a simultaneous 4% decline in reported problems in the control arm. Reported anxiety simultaneously increases by 3% in the intervention arm, but declines by 1% in the control arm.

The PEDS-QL dimensions follow a similar pattern to EQ-5D-Y outcomes. Health profiles are comparable at follow-up; however, observed differences between groups in health profiles at baseline mean that pupils in the two trial groups have experienced some difference in trends between time points. Both groups report a decline in ‘school function’ between time points, with a 6.98-point decline in the control arm and a 2.08-point decline in the intervention arm. ‘Emotional function’ decreases by 2.82 points in the control arm, but improves by 2.4 points in the intervention arm. There is greater similarity in trends in other dimensions, with both trial arms reporting a decline in physical function between time points (slightly larger in the control group), and small changes in social function showing a slight decrease in the control arm compared with a slight improvement in the intervention arm.

Comparing education outcomes at follow-up, teacher-reported Strengths and Difficulties Questionnaires reveal a greater number of more severe reported difficulties in the intervention arm than in the control arm. There is a 5% difference in reported difficulties, which are distributed among the two highest categorisations of pupil difficulties. When accounting for baseline values, however, an improvement in strengths and difficulties profiles is apparent in both arms, with a much stronger difference observed in the intervention arm. In the intervention group, there is a 7% improvement in the number of pupils categorised within normal ranges by teachers. There is an apparent improvement in reducing reports of both higher- and lower-severity difficulties. In the control arm, there is a 3% improvement in aggregated difficulties profiles. This is due to fewer pupils being classified as ‘high’ difficulty; however, there is a corresponding increase in the number of pupils with difficulties profiles still classified outside a ‘normal’ range. The results of complete-case analysis are presented in scenario analysis (see Report Supplementary Material 2).

Discussion

Aims and objectives

A scoping review was carried out to identify candidate economic models or comprehensive meta-analyses evaluating the effect of childhood sedentary behaviour on a range of long-term health outcomes. Sedentary behaviour can be defined as time spent sitting, lying or reclining accompanied by low levels of energy expenditure (1.0–1.5 METs). 1 Sedentary behaviours exist across various daily domains: in work, leisure and commuting. 33,139,140 Some distinctions between types of sedentary behaviour go further, categorising sedentary behaviours as discretionary (such as watching television or reading) and non-discretionary (such as sitting at school or during a commute). 141

Our primary research question was:

Are there existing economic or epidemiologic models that could be adapted for economic evaluation, which link childhood sedentary behaviour to expected short- and long-term health outcomes?

A secondary aim of our scoping review was to give an oversight of existing research into the link between sedentary behaviour and health outcomes to guide our methods of evaluation and highlight key issues in the field.

Our secondary research question was therefore:

What is known from the existing literature about the causal association between childhood sedentary behaviour and health outcomes?

In consultation with an information strategist, preliminary MEDLINE searches were carried out (see Search strategy). Only English-language publications were searched.

Search strategy

A comparison of initial search strategies is presented online in Report Supplementary Material 2. Search strategy 1 required article titles to contain ‘sedentary’ in the main title, whereas search strategy 2 allowed ‘sedentary lifestyle’ or variants to be contained in the main text of articles. Search strategy 1 identified 78 records, whereas strategy 2 identified 1540 records.

Abstracts from strategy 1 and a sample of 20 abstracts from strategy 2 were examined for relevance. Given the greater sample size of papers judged potentially relevant, search strategy 2 was selected, with the phrase ‘[review OR economic evaluation]’ added to the search terms to refine the search to more closely identify potential modelling studies. This search identified 208 papers, 182 of which were not duplicates.

All 182 abstracts were examined for relevance to the research question. Papers were examined in more detail if they were determined from the abstract to:

• examine associations with a quantified health effect (e.g. BMI, cognitive development, depression)

• consider a relevant population (i.e. aged < 16 years)

• use an objective measure of physical activity and/or sedentary behaviour

• include a study design that could indicate evidence of a causal association

• be a meta-analysis or systematic review, containing evidence regarding more than one health effect, or outcomes relevant for an economic evaluation (e.g. quality of life).

Articles were ranked according to these criteria to prioritise articles for review. There were 12 articles fulfilling four criteria and seven articles fulfilling all five criteria (one was at protocol stage). Results of the scoping review are shown in Report Supplementary Material 2.

Our scoping search revealed studies of varying quality, mostly in high-income countries; however, it also found some evidence gathered in a variety of low- and middle-income settings. The 33 papers examined highlighted some key themes within the field and identified further relevant references. It was apparent that many studies have been undertaken to ascertain population trends and general correlates of sedentary behaviour, as well as testing the effectiveness of interventions aimed to reduce sedentary behaviour. In this field, there was a good range of evidence type, including studies with defined control groups, some with randomised components. Health effects of sedentary interventions were, however, less often studied.

When examining sedentary time, proxies were often used, such as reported television viewing time, rather than objective measurement. The lack of objective measurement and uniform scale, and method of assessment, of sedentary behaviour made comparisons between studies difficult due to levels of heterogeneity in exposure, often hindering the usefulness of reviews or meta-analyses. The type of sedentary behaviour studied is important, with the possibility of health effects from television viewing, for example, to be mediated by unhealthy dietary patterns less common in people who spend more time in other sedentary behaviours (such as reading or studying). 17,142 Comparatively few studies aimed to specifically track sedentary behaviours to short- or long-term health effects in children. In gathering evidence for short-term health effects, comparatively few analyses convincingly account for residual confounding of physical activity levels. Our search highlighted a wider range of evidence for the health effects of sedentary behaviours in adults; however, our assessment of this evidence was limited by our choice of search terms, which explicitly attempted to focus on a paediatric and adolescent population.

Studies that examined health effects of sedentary behaviours in children most often focused on a limited range of outcomes, most commonly around cardiometabolic or adiposity outcomes. Most frequently, short-term outcomes were observed, such as high-density lipoprotein cholesterol or BMI. The six reviews ranked most relevant (i.e. those scoring 5/5) focus primarily on these outcomes; however, they also report other major outcomes. 12,14,142–145 The reviews present a mixed evidence base, with the most relevant reviews suggesting a negative impact of higher sedentary behaviour on paediatric health outcomes, particularly from observational studies not controlling for physical activity levels. The evidence base is, however, inconclusive or shows no health effect of sedentary behaviour in a paediatric population for prospective study designs or when physical activity levels or diet are controlled for. 12,144,145 A full summary of evidence presented in the reviews considered is presented in Report Supplementary Material 2.

Narrative summary of studies considered

Carson et al. ,14 de Rezende et al. 142 and Tremblay et al. 13 focus on non-prospective sources, as well as intervention studies. Perhaps due to the greater number of non-prospective sources considered, the direction of evidence presented suggests an association between lower sedentary time, lower BMI and improved psychosocial outcomes. Tremblay et al. 13 provide a meta-analysis for adiposity outcomes; however, all above papers use a narrative review as their main vehicle of evidence synthesis. No review attempts to control for levels of physical activity, neither do they readily differentiate the conclusions of evidence gathered from objective measures of sedentary behaviour from other sources. Authors cite heterogeneity in exposure and methods of outcome measurement in underlying studies as a limitation to further quantitative synthesis. Nevertheless, Tremblay et al. 13 conclude that the limited RCT evidence examined, ‘coupled with the qualitative syntheses of data from the other study designs, provides consistent evidence of the inverse relationship between sedentary behaviour and health outcomes’.

Biddle et al. ,144 Cliff et al. 12 and van Ekris et al. 145 take a more sceptical view of the evidence available. These reviews focus primarily on prospective studies or those using objective measurement of sedentary behaviours. Cliff et al. 12 provide an estimate of the health impact of sedentary behaviours controlling for moderate to vigorous physical activity levels. Although Carson et al. 14 argue against this approach, due to potential for collinearity in physical activity levels and sedentary behaviour patterns in a regression framework, Cliff et al. 12 nevertheless utilise this approach. As Cliff et al.’s12 focus was on evidence gathered from experimental sources (often based on multicomponent physical activity interventions), Carson et al. ’s14 criticism is less applicable. Carson et al.’s14 criticism is most pertinent for evidence gathered from observational sources, where causality is more difficult to attribute; thus, adjusted regression approaches may eliminate the intervention effect.

Cliff et al. 12 conclude that ‘there is limited available evidence that volume or patterns of sedentary behaviour are associated with health and development in children and young people, particularly from studies with low [risk of bias] that adjust for MVPA’. 12 van Ekris et al. 145 give an evidence synthesis stratified by sedentary behaviour type to help account for heterogeneity in exposure type. This analysis presents a small, non-significant increase in adiposity (BMI) for each additional reported hour of television viewing or computer use. There was no evidence of effect on adiposity in studies using objective measurement of sedentary behaviour. Biddle et al. 144 also conclude that studies using objective accelerometer measurement yield null association between sedentary behaviour (measured by screen time) and adiposity, despite a small dose–response relationship observed from cross-sectional evidence. Biddle et al. 144 conclude that there is no evidence of a causal association between sedentary behaviour and adiposity in youth using Bradford Hill criteria.

Results

The summary of the evidence base of the health effects of sedentary behaviour in children was surprising to us. The evidence base for adverse effects of childhood sedentary behaviour on common health outcomes was expected to be stronger. All authors acknowledge limitations in the evidence base, citing the need for more long-term studies in this area, particularly with robust study designs. Nevertheless, the observed divergence from evidence gathered in adults, for whom there is currently stronger indication of adverse health effects of sedentary behaviours, may have plausible explanation. Some authors suggest that children accumulate their sedentary behaviour in a different way to adults. 146 Altenburg et al. 146 found the children studied to spend ‘most of their sedentary time in bouts of ≥ 5 minutes’ and ‘bouts of ≥ 20 minutes were rare’. Meanwhile, adult studies indicate that prolonged uninterrupted sitting is especially detrimental for cardiometabolic health. 147–149 van Ekris et al. 145 therefore hypothesise ‘that frequent interruptions in children’s sedentary time may prevent them from negative health consequences’. The underlying biology may be the same, but the behaviour was sufficiently different to prevent this being observed.

An alternative explanation may be borne out in the inadequacy of measurement methods to detect sedentary behaviours accurately. Much research uses non-objective measures, such as self- or proxy-reported questionnaires, with serious risk of bias. However, Carson et al. 14 equally note that ‘accelerometers may not be sensitive enough to capture patterns in sedentary time’, and propose future research using inclinometers, ‘which can more accurately capture postures . . . to better understand the health impacts of patterns of sedentary behaviour’. 14,150 The authors therefore believe that the use of accelerometers as the primary instrument of measuring sedentary behaviour objectively limits the potential to find evidence of a health effect. Nevertheless, evidence of the paediatric health effect of sedentary behaviours from inclinometer measures is currently unavailable and therefore cannot be considered in economic model building. Perhaps more notably, evidence of the health effects of sedentary behaviours gathered using any means from screen time studies are likely to be largely incomparable with the in-school evidence generated in this study, if the possible mediating effects of increased snacking while sedentary during screen time is considered a plausible confounding effect. It is not expected that this mediating pathway would be observed to a similar degree within the school environment.

Introduction

This section presents long-term modelling estimating changes in health-related quality of life and health costs arising from changes in physical activity levels observed in the Stand Out in Class trial over a 30-year time horizon.

Methods

Results

Discussion: long-term cost-effectiveness modelling

Process evaluation overview

A series of interviews and focus groups with teachers, children and parents or guardians were conducted following the completion of the baseline measures and randomisation (phase 1), to explore the acceptability of the trial procedures, including randomisation (objective 5) and the acceptability of the measurement instruments (objective 6). Interviews/focus groups with teachers (n = 12 interviews), children (n = 12 focus groups) and parents/guardians (n = 7 interviews/focus groups) were conducted at each of the eight participating schools.

To help refine a recruitment strategy for a future trial, parents or guardians who did not consent their child to participate (identified by teachers who would know which parents had not consented) were asked briefly and informally by researchers visiting the schools at drop-off times or by teachers themselves if they would be willing to share their reasons for not consenting (objective 1). The acceptability of the intervention (objective 7) and children’s, teachers’, and parents and guardians’ perceptions and experiences of the intervention and outcome measures were determined at phase 1 and further explored towards the end of the intervention period (phase 2), through a further set of interviews (n = 4 with teachers from the intervention schools) and focus groups (n = 4 with children from the intervention schools) (objective 8). This included exploring any negative effects, such as discomfort from the monitoring equipment, reasons for non-compliance with the outcome measures or class disruption. Potential differences in the trial and intervention acceptability between ethnic groups were also explored as part of the analyses from the focus groups (objective 4). Towards the end of the intervention period, four interviews were conducted (with senior staff, head teachers/deputy head teachers) at each intervention school to further examine the acceptability of the intervention (objective 7). To assess intervention fidelity, intervention classrooms were observed by a member of the research team on two occasions and children’s posture during sit–stand desk use was recorded to assess any potential future risk of musculoskeletal injury.

Throughout the process evaluation, we used the conceptual framework of Hasson196 to guide the analysis of intervention fidelity and to explore adherence to the intervention (content, coverage, frequency and duration), and potential moderators of adherence to the intervention (including participant responsiveness, strategies used to facilitate implementation, quality of delivery and contextual factors).

Interview and focus group participants: acceptability and fidelity

For the interviews with participating teachers, the study co-ordinator contacted each teacher by e-mail or telephone to invite them to participate. Interviews took place at the school at a time of the teachers’ choosing. For the focus groups with children, teachers were requested by researchers to nominate three boys and three girls within their class who were confident and would want to participate in a focus group. Selected children were asked to take an information sheet and parental consent form home for their parents or guardians to read and to provide written consent for their child to participate in this phase of the research.

For the focus groups with parents and guardians, we aimed to conduct eight focus groups (one for each school) with parents and guardians who had given their consent for their child to participate in the trial. We aimed to have approximately four to six parents or guardians taking part in each focus group. The strategies employed to recruit parents/guardians to focus groups were (1) via a letter sent home from the school to parents and guardians with children who had consented to take part in the trial, detailing an exact time and date of when the focus group was going to take place (all focus groups took place in each of the schools); and (2) schools with a text message system (n = 3) sent out a reminder text on the morning of the focus group. Each of the eight teachers were asked whether or not a translator would be required before the day of the parent and guardian focus group. Only one focus group required a translator. The translator was a member of the Born in Bradford research team who had prior knowledge on the topic guides and the purpose of the focus group. All other focus groups were conducted in English.

Prior to the start of the parent and guardian focus groups, the purpose of the session was described and participants were requested to provide written informed consent. Finally, for the interviews with head teachers and senior members of staff, the study co-ordinator contacted each of the school’s head teachers and senior members of staff by e-mail or telephone to invite them to participate in an interview at the end of the study, to inform the context part of intervention fidelity.

Interview and focus group procedures: acceptability and fidelity

All of the interviews and focus groups, across both phases, used semistructured topic guides (see Report Supplementary Material 3) to ensure consistency. Questions were open ended to enable participants to raise issues important to them. Topic guides for focus groups with children were written in a language suitable for children aged 9–10 years. All interviews and focus groups were audio-recorded digitally.

Informal conversations with non-consenting parents, guardians and children: acceptability

For the informal conversations with non-consenting parents, guardians and children, teachers or researchers spoke to parents and/or children and simply asked ‘what were the reasons for not signing up to be part of the study?’. Researchers and/or school staff recorded the answer given to the question, along with the child’s sex and what relation the parent or guardian was (e.g. mother, father, grandparent, carer). This approach was taken as teachers felt that asking parents and children to a formal focus group or interview to speak about the trial in which they did not want to participate would possibly make them feel uncomfortable and less likely to speak openly.

Classroom observations: assessment of intervention fidelity and musculoskeletal discomfort

As part of the pilot assessment of intervention fidelity, intervention classrooms were observed by a trained researcher for the duration of at least half a school day (3 hours) during the spring (March, April and May) and summer (June, July and August) terms. Therefore, a total of eight observation periods, two per intervention school, took place. During the observation periods, the researcher used an adapted version of the postural observation technique developed by Benden et al. 63 to observe individual children’s postures while working at a height-adjustable desk (either sitting on a stool or standing), during class time. This was to assess potential future risks of musculoskeletal injury (objectives 8 and 9). The observation of individual children lasted for 10 minutes, with the researcher first positioning themselves such that they were able to see the sagittal plane of the individual child. The researcher then started a stopwatch and used the Benden et al. 63 postural observation sheet (see Report Supplementary Material 3) to identify the posture that most closely resembled the position of the child at the start of every minute for 10 minutes. During the 10 minutes, whether the child’s neck was in extension or flexion, or whether or not the child was resting their elbows and/or forearms on the workstation was also recorded.

The sex of each child was also documented by the researcher, along with the time, lesson/subject and month of the year. If a child was absent from their desk at the beginning of a minute during the 10-minute observation, the researcher marked an ‘X’ and treated it as a missing data point for analysis. Similarly, if the observed child moved during a minute of data collection, the researcher noted it in the ‘comments’ section of the data collection sheet.

The fidelity observations occurred at the same time on the same day as the posture observations. While present in the classroom, researchers had informal conversations with children during natural breaks of the day about each of the intervention components. Researchers also observed and tallied the number of boys and girls either sitting or standing while using the sit–stand desks every minute during the posture observations; this measure provided minute-by-minute data of how the sit–stand desks were being used during class time.

Two researchers conducted both posture and group (fidelity) observations. The interobserver agreement, using interval-by-interval agreement was ≥ 85% for each component of the observation tools.

Qualitative data

Audio-recordings were transcribed verbatim with anonymisation of all personal data. Interview data were then analysed using thematic analysis. 197 The process involved the following steps.

Interview and focus group participants

Objective 1: to support the refinement of a recruitment strategy for schools and pupils

Objective 5: assess the acceptability of randomisation to schools

When asking teachers and children about the acceptability of randomisation, both groups expressed that there was a clear understanding of why the randomisation had occurred:

Well yeah because it makes it fair doesn’t it, it keeps everything on a level playing field and you wouldn’t necessarily want to choose your school because you are hand picking, whereas if you randomise it you make it really clear that you have got an equal chance of having desks in and going through doing those, so it just keeps everything fair doesn’t it really.

Teacher, I2, SA

Because then you can look at the schools that have the tables and the schools that didn’t and look at the difference in health.

Child, I3, WB

This was true even with teachers and children from the control schools, who were understandably disappointed not to be receiving the sit–stand desks. However, they still considered their participation in the trial to be positive and clearly understood why it was required:

Well, I completely understand why you need to have a control. You know, we teach the children, that certain investigations need a control, you need something to compare it against . . .

Teacher, C3, SA

Well a bit sad but I felt happy at the same time because at least we’re taking part in something.

Teacher, C4, SA

As for parents and guardians, most thought that it was a fair process:

I think it’s fair, it’s a fair process because it doesn’t . . . it’s a neutral process as well so there’s no bias towards anything and pick and choose, schools that could be biased there so this was like totally random, I think it was fair.

Mother, I2, SA

Objective 6: assess the acceptability of measurement instruments to teachers, children, parents and guardians, including the activPAL inclinometer as the tool for the measurement of the primary outcome

Objective 7: assess the acceptability of the intervention to teachers, children and parents

Randomisation into the trial conditions occurred following baseline data collection (January 2017). The sit–stand desks (Ergotron LearnFits) were installed into the intervention classrooms at the very beginning of March 2017; the delay in desk installation was caused by shipping delays experienced by the desk manufacturer. Before the desks were installed, the researchers met with the teachers to provide them with training on the various intervention components. The teachers were provided with the Stand Out in Class training manual (see Report Supplementary Material 1) and a member of the research team met with each intervention teacher individually for approximately 1 hour, when they explained the various intervention components. During this meeting, the researcher encouraged the teacher to consider how they could rotate children in their class across the week, to ensure equal exposure to the desks. The teachers were also asked to consider how they could implement other intervention components.

Once the sit–stand desks were installed and on the first day of exposure to the desks, the researchers led a children’s workshop within each intervention class (including all children in the classroom), in which the various intervention components were described. This workshop concluded with all children, and their teacher and any teaching assistants, signing the social contract. During this visit, the researcher also discussed with the teacher their thoughts on a rotation plan for exposing children to the sit–stand desks and answered any remaining questions about the intervention.

The first phase of the qualitative work to examine the acceptability of the intervention centred around participants’ initial thoughts and experiences of using the sit–stand desks. This information was gathered from focus groups with the children and parents, and through interviews with the teachers conducted a few weeks after the installation of the sit–stand desks (phase 1). Further insights into all intervention components (the desks, training provision, nudging prompts, the social contract, researcher/practitioner support) were gathered towards the end of the intervention (phase 2) through a second set of interviews (with teachers) and focus groups (with children).

Objective 8: monitor any adverse effects, such as musculoskeletal discomfort and/or disruption to the classroom or learning, to inform the design of a full trial and minimise or eliminate any such effects

Objective 9: assess intervention fidelity over the intervention period

We report intervention fidelity against the framework of Hasson,196 and fidelity (whether or not the intervention was implemented as planned), dose (frequency and duration of the intervention), reach and contextual factors are reported below. Participant responsiveness to the intervention (e.g. acceptability) is discussed in detail above (see Objective 7: assess the acceptability of the intervention to teachers, children and parents).

Objective 1: establish and refine a recruitment strategy for schools and pupils

A total of 24 eligible schools were approached for recruitment into this pilot study and the target number of eight schools consented to take part (recruitment rate = 33%). This recruitment rate is similar to recruitment rates seen in other primary school-based interventions located in this region201 and elsewhere in England. 202 The eight recruited schools were located predominantly in urban areas throughout the Bradford metropolitan district. Across the eight schools, an average of 17.1% of pupils were eligible for free school meals; this figure matches the 17.2% of children across all schools in Bradford eligible for free school meals, suggesting that the recruited schools were largely representative of schools within this area. Similarly, the proportion of children eligible for free school meals from the 12 schools that declined to participate was 17.4%. In England, in 2017 (the time of the intervention), 14.8% of children were eligible for free school meals,113 demonstrating the slightly higher levels of deprivation within this study setting.

The recruited schools tended to have a higher proportion of children whose first language was not English (51.4%) than schools that declined to participate (38.4%), and schools in Bradford overall (42.3%). 113 In England, in 2017, 20.6% of primary school children were registered as having English not as their first language, highlighting a greater ethnic diversity in the study sample and Bradford population than in national-level data. 113 Of interest, the schools opting into the study were more likely to contain a higher proportion of South Asian children, with schools declining to participate being more likely to contain white British children (8 out of the 12 declined schools). This finding highlights that the present study was effective in recruiting a diverse range of schools into the study, in terms of the ethnic distribution of their pupils; however, additional strategies to recruit schools containing a higher proportion of white British children may need to be incorporated into a full trial.

Within the participating schools, 75% (n = 176) of eligible pupils provided parental consent and written assent to participate in the evaluation measures, which exceeded our target minimum sample size of 120 participants. This recruitment rate is higher than that seen in a recent RCT (59%) examining the effectiveness of a healthy lifestyle programme [the West Midlands ActiVe lifestyle and healthy Eating in School (WAVES) children study] conducted in primary schools from the West Midlands,202 and similar to that reported (79%) in a primary school-based sit–stand desk intervention in the USA. 203 Overall, this pilot RCT has demonstrated the feasibility of our recruitment strategy for both schools and children into the Stand Out in Class study.

Objective 2: determine attrition in the trial (schools and children)

All eight participating schools completed the trial, leading to a 100% school retention rate. At 7 months’ follow-up, the overall retention rate of participating children was 97% (96% from the control group and 98% from the intervention group). Fifty per cent of children not returning for the follow-up measures had moved away from the area during the study and, hence, changed schools.

Objective 3: determine completion rates for outcome measures (and whether or not these are sufficiently high to provide accurate data in a full trial)

Completion rates for the outcome measures ranged from 63% to 97%. The highest completion rates were seen for the anthropometric (94%) and questionnaire-based measures (97%), with the completion rates for these measures being comparable to those reported in the Active for Life Year 5 cluster RCT, a school-based intervention targeting physical activity, sedentary behaviour and fruit and vegetable consumption in children. 119 The lowest completion rate (63%) was observed for the activPAL, with a number of children not providing valid data from this device across the two measurement periods. The proportion of children providing valid activPAL data in the present study is higher than that observed previously in a similar group of children29 and identical to that observed in a recent sit–stand desk RCT in Belgian children. 204 These numbers are lower, however, than those observed (> 90% compliance) in other (non-RCT) classroom-based sit–stand desk interventions in which the activPAL was the primary outcome. 68,205

In comparison with the activPAL, rates of compliance with the wear time criteria for the ActiGraph were higher (83%) when the same wear time criteria were applied (≥ 8 hours on at least 1 weekday). In the Active for Life Year 5 study, 60% of participants complied with their ActiGraph wear time criteria (≥ 8 hours of wear on at least 3 days206). 119 Applying the same criteria to the ActiGraph data in the present study would have resulted in 68% of our sample providing valid data at baseline and follow-up, confirming the feasibility of this device. The acceptability of the activPAL as the proposed primary outcome measure for a definitive trial is discussed further in Objective 6: assess the acceptability of measurement instruments to teachers, children, parents and guardians, including the activPAL inclinometer as the tool for the measurement of the primary outcome. This pilot RCT has highlighted the need for further research to examine how wear protocols can be improved for the activPAL to increase compliance. Aside from this measure, however, completion rates for the remaining measures examined herein were sufficiently high to provide accurate data in a full trial.

Objective 4: assess whether or not there are any differences in trial recruitment, retention and acceptability between ethnic groups

There were no observed differences in trial recruitment, retention or compliance rates between South Asian and white British children. Ninety-eight per cent of white British and South Asian children provided parental consent and written assent to participate in the trial evaluation, and retention rates of 98% were observed in both ethnic groups. Sixty-five per cent of white British children and 68% of South Asian children provided valid activPAL data, whereas 87% and 84% of children within these ethnic groups provided valid ActiGraph data, respectively. No themes emerged during the process evaluation to indicate differences in the acceptability of the trial or intervention between different ethnic groups.

Objective 1: establish and refine a recruitment strategy for schools and pupils

Teachers, children and parents all considered the recruitment approach adopted to be appropriate and teachers liked how the study was explained to children by the research team during classroom visits. As highlighted in Trial feasibility-related outcomes (objectives 1–4), Objective 1: establish and refine a recruitment strategy for schools and pupils, 75% of eligible pupils from the participating schools provided parental consent to participate in the trial evaluation. Informal conversations with parents who did not provide informed consent for their child to participate revealed that the most common reason for this was that parents were unaware of the study, through not receiving or not reading the study information sheet sent home with their children. A future trial should explore with schools additional options to inform parents and guardians about the study, such as inclusion of a brief mention of an up and coming study in electronic school newsletters, for example, or via schools’ social media platforms.

Objective 5: assess the acceptability of randomisation to schools

The process of randomisation was regarded as acceptable and fair by teachers, children and parents, and although participants from the control schools expressed disappointment at being randomised into the control arm, participants understood why a control condition was needed. Control arm teachers stated that participating in the study was still a positive experience for their class.

Objective 6: assess the acceptability of measurement instruments to teachers, children, parents and guardians, including the activPAL inclinometer as the tool for the measurement of the primary outcome

The majority of the measurement instruments used within this pilot trial were deemed to be acceptable by teachers, children and parents. Teachers reported that some children experienced irritation on their legs caused by the medical dressing used to attach the activPAL; however, they reported that this occurred in a small minority of children and did not feel that it was a big issue. However, some children also reported that the medical dressing was ‘problematic’ and this was echoed by some parents. Concerns regarding the attachment of the activPALs are reflected in the compliance data reported in Trial feasibility related outcomes (objectives 1–4), Objective 3: determine completion rates for outcome measures (and whether or not those are sufficiently high to provide accurate data in a full trial. Children reported generally preferring the ActiGraph and this was reflected by the higher compliance data seen for this device.

Further research should examine different attachment options for the activPAL in children. In the present study, we adopted a 24-hour wear protocol, with the anticipation that the hypoallergenic Hypafix dressing would stay on the skin for a number of days, and not require children to frequently take the device (and dressing) on and off. This approach has been used successfully in a recent sit–stand desk intervention with 11-year-olds. 68 Other researchers, however, have enclosed the activPAL in a small pocket in an adjustable elasticised belt that is worn at the mid-anterior position of the thigh throughout waking hours only and removed for any water-based activities. 38 This attachment option resulted in high compliance rates (> 90%) in a recent sit–stand desk intervention in 10- to 11-year-olds and has been used successfully in a cross-sectional study with > 200 8- to 11-year-olds. 150,205

Other researchers have recently used the ActiGraph placed on the anterior aspect of the thigh attached using an elasticised belt as the primary outcome measure in recent sit–stand desk interventions in schools. 66,207 When mounted on the thigh, the ActiGraph inclinometer algorithm has been found to be a valid and reliable method of measuring sitting and standing postures. 208,209 The utility of the ActiGraph worn on the thigh and the activPAL placed within an elasticised belt should be explored in a sample of primary school children within the UK, to inform a definitive trial.

Children reported that the RVIP task was difficult and this is reflected by the relatively low levels of accuracy recorded on this test. This test has previously been used in slightly older samples of school children (12- to 13-year-olds),101 and may, therefore, not be appropriate for younger age groups. Some parents reported the health-related resource use questionnaire burdensome to complete and this is reflected in the low completion rate for this measure. Future studies should investigate more appropriate methods of obtaining this information from parents to inform economic evaluations.

Objective 7: assess the acceptability of the intervention to teachers, children, parents and guardians

Initial thoughts about sit–stand desks being installed within classrooms were generally very positive by teachers, children and parents. After a few weeks of the desks being installed, teachers’ views of the intervention remained positive and any initial apprehensions about the desks (including any potential negative impact on handwriting and general behaviour) were not experienced. Towards the end of the intervention, teachers commented on how the desks were now regarded as part of the norm within their classrooms. The overall design and features of the desks, including their wheels, which enabled them to be moved easily, were highlighted as positives by teachers. These comments about the desks fitting in within the classroom and their portability are in agreement with interview data collected from a high school teacher in the USA following installation of six LearnFit desks in their classroom over a 9-week period. 210

Similar to the teachers, children were very positive about the desks throughout the intervention. A number highlighted that their comfort levels when working at the desks improved and some reported feeling healthier by standing up. A number of the children reported that they liked having their own space and they liked having the option to sit or stand when using the desks. These comments about space and having the option to sit or stand mirror those from a sample of 11- to 14-year-olds from a US middle school exposed to six LearnFit desks over 9 weeks. 210 Some children in the present study reported that they felt that the desks improved behaviour within the classroom. This is something that has been reported previously by parents interviewed following a pilot sit–stand desk intervention in a primary school in Texas. 58 In the Texas study, 61% of parents interviewed reported that they felt that the sit–stand desk had a positive impact on their child’s behaviour at school. In the present study, parents were also positive about the intervention, commenting that they liked how the desks promoted movement in class.

Teachers found the training component of the intervention very helpful and found the examples of how they could rotate children around in their class to ensure equal exposure to the desks useful. The project manual provided to teachers after the training, and the use of the nudge cards, were not deemed necessary, however, by the majority of teachers, as they felt confident to deliver the intervention after the training session. Overall, findings from the process evaluation suggest that the Stand Out in Class intervention is acceptable to teachers, children and parents.

Objective 8: monitor any adverse effects, such as musculoskeletal discomfort and/or disruption to the classroom and learning, to inform the design of a full trial and minimise or eliminate any such effects

There were no reports of any adverse effects associated with the intervention in terms of musculoskeletal discomfort reported by children, or disruption to the classroom reported by teachers or children. These findings agree with others who have concluded that sit–stand desks can be introduced into the classroom environment without having a negative impact on student learning, behaviour or musculoskeletal comfort, and without causing classroom disruption. 65,67,205,207,210 Indeed, some evidence suggests that sit–stand desks can have a positive impact on musculoskeletal comfort, with improvements in comfort ratings being observed in children following sit–stand desk use. 63,207

Objective 9: assess intervention fidelity over the intervention period

Limited evidence currently exists on the fidelity of sit–stand desk interventions within the classroom environment. 210 We undertook two classroom observations in each intervention school, one in the spring term and one in the summer term, to examine the fidelity of the Stand Out in Class intervention. It was clear from all observations that all sit–stand desks were being used across all intervention classes. However, the intervention differed slightly across intervention schools as the trial progressed. Two teachers decided to move the provided stools away from the desks to encourage children to stand at the desks, whereas in the remaining intervention schools, the stools were kept with the desks. Throughout the study the intervention teachers also modified how they rotated children around the class to be exposed to the desks. Only one teacher used the per-protocol rotation plan recommended during the training, which involved rotating groups of children at half-daily intervals; two teachers rotated children on a daily basis, so each group of children was exposed to the desks for 1 day per week; and one teacher rotated children on a weekly basis. Following contact with the research team about this rotation plan, this teacher modified it and agreed to rotate the children more frequently. Despite differences in how children were exposed to the desks, it was clear from the classroom observations and qualitative research with teachers and children that all children had access to the sit–stand desks throughout the trial, and all teachers tried to ensure that desk exposure was fair across their class. Although we observed some deviations from the intervention protocol, the observation that teachers started to utilise the desks in their own way suggests that the intervention may have real-world applicability and feasibility.

The addition of more sit–stand desks in classrooms, such as making up 50% of classroom furniture, as suggested elsewhere,210 could be a feasible solution for a future trial. This would probably make it easier for teachers to rotate children around for desk exposure and also, importantly, increase the dose of the intervention. Overall, in the present study, all intervention schools were fully committed to the trial, and participating teachers had the full support of head teachers and senior staff.

Objective 10: derive preliminary estimates of the effect of the intervention on children’s total daily sitting time, physical activity, indicators of health (markers of adiposity and blood pressure), cognitive function, and academic performance, engagement and behaviour

A weighted linear regression model, after adjustment for mean baseline weekday sitting time and mean wear time across the measurement time points, revealed that children in the intervention group spent less time sitting than children in the control group did at follow-up. The mean difference (weighted by school size) in change in sitting time over the intervention period was –30.6 minutes per day (95% CI –56.42 to –4.84 minutes per day) between groups. This is a greater reduction in daily sitting time than that observed in a recent sit–stand desk RCT conducted in primary school children in Belgium, in which, relative to the control group, the intervention group experienced a reduction in daily sitting of –13.5 minutes per day at 8–12 weeks’ follow-up. 204 In this study, however, only three sit–stand desks were placed in the classrooms of the intervention schools, which probably explains the reduced effect of the intervention on total daily sitting time. Based on the current findings, and those of Verloigne et al. ,204 it would be logical to suggest that adding more sit–stand desks to the classroom environment, and thus increasing the exposure and ‘dose’ of the intervention, would probably result in even greater reductions in daily sitting time. If examined over a longer time period, with sufficient power, such a study would fill an important gap in the literature by investigating the impact of this intervention on markers of health in children, as discussed in further detail below.

To date, most sit–stand desk interventions in primary schools have reported within-group differences in sitting time over the intervention period, with reductions in mean weekday sitting times ranging from 12 minutes per day to 80 minutes per day in intervention groups. 29,67,68,205,207 Of the few studies that have drawn comparisons between changes in weekday sitting times between intervention and control participants, changes between groups have ranged from +19 to –66 minutes per day. 68,204,205 Although preliminary, this study adds to the very limited evidence base204 from a cluster RCT on the potential impact of a classroom sit–stand desk intervention on changes in weekday sitting time.

No data currently exist in children to inform the magnitude of a reduction in sitting time needed to bring about changes in health markers. Although such optimum reductions in sedentary time in children need to be established to inform public health messaging, data from adults have demonstrated that reallocating just 30 minutes of sedentary time per day to light movement is associated with a 2–4% improvement in cardiometabolic biomarkers. 114 An earlier meta-analysis of RCTs and non-RCTs, examining sedentary behaviour interventions delivered in the school or home environment, reported an overall decrease in children’s sedentary behaviour of 18 minutes per day. 211 The preliminary findings from this study hold promise, therefore, and support the need for further RCTs examining the impact of sit–stand desks in the classroom environment.

Preliminary findings from this study revealed that reductions in sitting and increases in physical activity occurred in both groups after school, suggesting no evidence of compensatory behaviours occurring within the intervention group outside school hours, as reported elsewhere. 67,68 However, these findings should be treated with caution due to the confounding variable of measurement season (see Strengths and limitations).

There were no observed changes in measures of body composition or blood pressure within this study. However, significant reductions in BMI percentile have been observed in a sample of 7- to 9-year-olds exposed to sit–stand desks over a 2-year period in three US primary schools. 203 In the same study, non-significant reductions in BMI percentile were also observed in children exposed to the sit–stand desks for 1 year. In this US study, all standard (seated) desks were replaced with sit–stand desks, suggesting that the intervention ‘dose’ was greater than that observed in the present study. However, as in the present study, stools were provided with the sit–stand desks and children could choose whether to sit or stand throughout their lessons. Sitting time was not directly measured in this study, therefore it is unclear by how much sitting time was reduced over the 1- and 2-year periods. This evidence, however, suggests that such a treatment effect of this simple intervention (i.e. providing children with more opportunities to stand while learning) may be seen over a longer exposure period, with a greater intervention dose, and this should be examined in a definitive trial.

Improvements in cognitive function were seen in both groups, suggestive of a potential learning effect of the cognitive test battery. To date, findings of the impact of sit–stand desks on cognitive function are inconclusive, with preliminary (non-RCT) evidence suggesting that sit–stand desks have a positive impact on some measures of cognitive function, whereas other evidence suggests no effect. 66,212 No evidence currently exists, however, that suggests that sit–stand desks have a negative impact on cognitive function.

Pupil behaviour conduct in the classroom and interactions with fellow pupils were examined using the teacher-reported Strengths and Difficulties Questionnaire. Preliminary observations from this measure indicated that the intervention group generally had reduced antisocial and hyperactive behaviours and increased self-control than the control group at follow-up. Interview data from teachers from US primary and high schools have highlighted observed improvements in behaviour when children use sit–stand desks,58,210 with teachers reporting that student attention and engagement increased during standing.

In this study, we demonstrated the feasibility of collecting academic progress data for maths, reading and writing from schools. However, as data relating to pupils’ progress across these key subject areas are not a requirement of the national curriculum for schools to collect, the lack of standardisation of this measure across participating schools made the interpretation of these data difficult, as we used routine data collected by each school to avoid placing additional burden on schools. When planning further research in this area, consideration in partnership with head teachers and teachers/assessment co-ordinators via PPI should be given to identify appropriate national curriculum-related/standard assessments routinely used by schools, which will enable direct comparisons between participating schools. In the absence of consensus over such measures, proxies of academic progress, such as attendance and/or in-class behaviour data, which can be measured consistently across schools, should be identified in collaboration with head teachers/teachers. Improvements in these measures would also be beneficial to inform an economic evaluation from an education perspective.

Objective 11: estimate the standard deviation of the primary outcome to inform a sample size calculation for a full randomised controlled trial

In this pilot study, a pooled SD of 95 minutes per day was observed in change in school day (weekday) sitting time, the proposed primary outcome in a definitive trial. Using this value, the sample size for a full trial was calculated to be 1276 participants from 58 clusters in total (638 participants and 29 clusters per arm). The sample size incorporates a 25% inflation to allow for losses to follow-up and missing data, along with the addition of one extra school in each arm to allow for whole-cluster dropout.

Objective 12: determine availability and completeness of economic data and conduct a preliminary assessment of potential cost-effectiveness

This study has demonstrated that it is feasible to conduct an economic evaluation alongside a cluster RCT of a sit–stand desk intervention within the classroom environment. Our preliminary analysis suggested little evidence of an effect in within-trial or extrapolated economic analyses. Based on current evidence using the most plausible scenarios, the intervention is unlikely to be cost-effective over a 30-year time horizon at a threshold of £30,000 per QALY. However, the Stand Out in Class intervention is typical of broader public health interventions, in that its comparatively small cost and QALY gain result in an ICER that is very sensitive to small changes in intervention cost and effectiveness. 213

Comments on trial design and implementation: suggestions for improvements for a definitive trial

Cluster randomisation appears to have been ineffective in balancing ethnic characteristics between trial arms despite stratification of schools on ethnic characteristics with the intention to achieve ethnic balance. Methods to improve ethnic balance and, therefore, improve precision in estimation of any hypothesised variation in treatment effect across ethnic groups should be considered in any future trial. Incorporation of a range of schools with different deprivation profiles would also add to understanding of which groups benefit most from any such intervention and could be used to inform a distributional cost-effectiveness analysis. No attempt was made to control for ethnic imbalance in all analysis of treatment effect, with multiple imputation only rebalancing missing data within known ethnic categories.

The trial treatment ‘dose’ should also be considered in the light of comments regarding low compliance with the trial protocol rotation plan. If possible, more than six sit–stand desks should be incorporated into the classroom environment to ascertain whether or not the observed treatment effect follows a dose–response relationship.

Areas for future work

We did not investigate the sensitivity of our conclusions to variation in the cost of sit–stand desks and whether or not this was viewed as an incremental cost over replacement of existing worn-out school furniture like for like. There is considerable variation in the cost of standing desks between different model designs and uncertainty in how best to incorporate any costs into economic modelling over their expected time horizon. A recent research briefing suggested that the unit price of a classroom standing desk varies from £25 for a basic model to > £600 for a sophisticated model. 214 How accounting costs are considered is likely to have an impact on cost-effectiveness judgements. There is a valid query of the viability of individual schools being able to cover the high upfront cost of a standing desk intervention, without additional cost of financing over several years. The same research briefing indicates an approximate cost of £270,000 to equip a whole school with standing desks costing £300 each, equipping 30 classrooms, each capable of holding 30 students per class. 214

As costing was conducted as a static classroom in this analysis, with no account of periods of non-use, costing assumptions at the school level would require change, given the current structure of UK primary school teaching, with asset usage being somewhat dynamic, unlike, for example, Italy, where teachers rather than children rotate between classrooms. If an intervention was extended to the whole school, incremental cost-effectiveness estimates may require consideration of children having access to standing desks in more than one classroom for lessons in different subjects. This would mean a higher cost per child, calculated as the total cost of desks in all classrooms divided by the expected population of the whole school over the expected lifespan of the desks.

At the increment, as in this study, the cost of setting up and maintaining these desks was not an important consideration; however, on a whole-school scale, consideration of these costs is likely to be relevant, with the benefit of an ‘active classroom’ environment needing to be compared with the opportunity cost of other potential investments forgone because of expenditure.

The main barrier to the current research agenda is an absence of evidence of an independent health effect of sedentary behaviours on generalised health measures, such as the QALY. Current evidence of health effects reported in intermediate health outcomes have inconclusive effect on measures that have meaningful impact on health-related quality of life. It is acknowledged that further research is needed to explore the impact of low-intensity activity on child and adolescent health, with interest in not only the volume of activity but also the distribution of activity throughout the day and school week. 4,23

Within the existing modelling approach, future work to assess a range of plausible values for the decay parameter in health effect would be particularly valuable, given extreme modelled sensitivity to this parameter. The rate of decay in activity levels, or corresponding health effect, is likely to interact with other environmental factors, including the spread of active workstations and other active living interventions across regions and throughout the life course. Models linking non-health outcomes of physical activity changes to desirable general outcomes (such as improved attendance, classroom behaviour, progress/attainment) would similarly be a valuable addition to analysis, in helping understand the importance of the possible non-health benefits of the Stand Out in Class intervention and similar interventions. A lack of available evidence has prevented further examination of outcomes outside health at this time.