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Sedentary behaviour among Scottish youth: prevalence and determinants

Acknowledgement

Thanks are expressed to Len Almond and Nick Cavill for their input to the early conceptualisation of issues, and to Jacqui Cole and Chloe Grimmett for assistance in Year 1.

Summary

1. There is a great deal of concern about young people’s overweight and obesity. Sedentary lifestyles are thought to be particularly important in weight gain yet it is common in the popular media and academic literature to simplify matters by stating that electronic media, such as the television and computer games, are primarily the cause of a ‘couch kids’ culture.
2. Project STIL (‘Sedentary Teenagers and Inactive Lifestyles’) at Loughborough University is research focusing on a wide range of sedentary and physically active behaviours. Project STIL (Scotland) investigated a Scottish sample with the dual purpose of a) obtaining estimates for the prevalence of sedentary behaviour in Scottish youth, and b) investigating factors associated with sedentary behaviour.
3. The principal data collection instrument was a self-report diary of “free-time” behaviours that school students completed outside of school hours (3 weekdays and 1 weekend day). The diary asked the participants to write down what they were doing at 15-minute time intervals. In addition, they recorded where they were. Demographic variables were also assessed.
4. Assessment took place in 27 schools from 14 local education authorities. Data were collected in two phases: October-November 2002 and February-May 2003 with school Years S2-S4 (ages 13-15 yrs). The final sample comprised 396 boys and 620 girls (total n=1016).
5. Boys averaged just over 2hrs TV viewing per day during the week and 3hr and 15mins at weekends; boys in Year S4 watched less TV than those in Years S3 and S2. Girls averaged just under 2hrs of TV viewing per day during the week and 2hr and 39mins at weekends; girls in Year S2 watched more TV than those in Years S3 and S4.
6. Other prominent sedentary behaviours included motorised travel, computer use, homework, and ‘hanging out’ with friends.
7. Boys were markedly more active than girls in sports and exercise
8. Results were minimally affected by ethnicity and socio-economic status.
9. Relationships between TV viewing and physically active behaviours were very small.
10. After school, there was a slight shift in likelihood of behaviour from motorised to active travel compared to before school, suggesting that active travel is possible for some children who use motorised means of travel to school.
11. The greatest likelihood of playing sport and exercise during the school week was in the early evening, whereas the likelihood of watching TV peaked later, suggesting some temporal displacement between the two behaviours.
12. There was never a time during the week when sports and exercise were more likely than TV viewing, but sports and exercise were more likely during periods of the weekend day for boys.
13. TV viewing was no greater for those with TV sets in their bedroom than those without, although for those with TVs in their bedroom, there was a 26% chance of watching TV, when in the bedroom, for girls and 35% for boys during the week, and at weekends 40% for boys and 29% for girls.
14. Physical activity was an inverse predictor of a cluster of sedentary behaviours, and the prediction was enhanced by accounting for the time young people spent outside. Interventions should focus on increasing opportunities for time outside of the house, requiring a mix of initiatives, ranging from structured activities, such as some sports, to environmental modifications based on attractiveness, accessibility, and safety.
15. While high and low TV viewing groups do differ in the amount of sports and exercise and time outside, the effect sizes are small-to-moderate.
16. When considering high and low sedentary groups, the amount of sports and exercise and time outside show much greater differences, all revealing large effect sizes. This confirms our view that while TV viewing is a prevalent sedentary behaviour, it is a not a good marker of total sedentary behaviour. Interventions might be better targeted at a profile of several sedentary behaviours rather than TV alone, as well as time spent outside.
17. Using cluster analysis, diverse groupings across sedentary and active behaviours were found for both boys and girls. This suggests that no one sedentary behaviour is likely to be an effective intervention target for the majority of adolescents. In addition, the clusters confirmed that TV viewing is not necessarily in opposition to sports and exercise.

Introduction

A great deal of media coverage has been devoted to the issue of physical inactivity in children and young people. Do they watch too much TV and sit for too long at the computer? Does this mean that they do inadequate amounts of physical activity? These are key questions we do not have definite answers to. This project was established to investigate the amount and types of sedentary behaviour in Scottish adolescents and what factors are related to sedentary behaviour.

Concurrent with this project, we collected data for the UK, through Project STIL (‘Sedentary Teenagers and Inactive Lifestyles’) but sampling estimates meant that only 4 schools in Scotland were assessed. There was a need, therefore, for a larger, more representative, Scottish sample for reliable estimates for the prevalence of sedentary behaviour. Additional funding was therefore offered in 2002 by the young People’s Programme at NHS Health Scotland¹ to increase the size of the Scottish sample to make it more representative.

Project STIL (Scotland) addressed two fundamental questions concerning sedentary behaviour outside school time in adolescent boys and girls in Scotland:

2. Measurement of sedentary behaviour in youth

2.1 Method

The principal data collection instrument was a self-report diary of “free-time” behaviours that school students completed outside of school hours. Because we were primarily interested in behaviours where young people had some element of choice, behaviours in school were not assessed. The diary was based on principles of Ecological Momentary Assessment (EMA) and was divided into two parts. The first involved questions about child-level variables (9 items; “About You”), family-level variables (11 items; “About your Family”), and environmental-level variables (15 items; “About your Home”) that have been hypothesized to correlate with sedentary behaviour and physical activity. The second part was for recording the behaviours and locations that young people engage in each day in their free time. Reliable estimates of behaviour have been found (Marshall, Biddle, Murdey, Gorely, & Cameron, 2003) .

Participants were asked to complete the diary for four days (three weekdays and one weekend day). At 15-minute intervals, participants self-reported (free-response) their main behaviour in response to a single item: “What are you doing now?”. At each interval, participants also responded to the closed-response items “Where are you?” (LOCATION) by selecting one location from a list of 12, and “Who’s with you?”. This last question will not be analysed and reported here due to limitations of space. An example diary page can be seen in Appendix 1.

Data collection days were randomly assigned by weekday and weekend day. For each weekday, 44 time-samples were obtained (one every 15 minutes from 07.00h to 08.45h and from 15.00h to 23.45h). For the weekend day, 68 time-samples were obtained (one every 15 minutes from 07.00h to 23.45h). To control for different levels in school-based physical activity affecting out-of-school behaviour, two items assessed participation in physical education (“Did you take part in a PE lesson today?”) and engagement in moderate-to-vigorous physical activity (“At school today, did you run round or breathe hard enough to make you sweat?”). At the end of each diary day, participants also responded to an additional 10 closed-response items that solicited information about snacking behaviour during the day and events that may have affected diary entries (e.g., weather, injury/illness, etc.).

The behaviours were first coded into 23 mutually exclusive categories. To estimate the time spent in each behaviour category, at each location, and in each social context, the interval-level data were aggregated for each individual (separately by weekday and weekend day) by multiplying the daily frequency of the event by 15 (1 interval = 15 minutes). The weekday data were then aggregated further to produce a mean, in minutes per day (min.day ^-1), across weekdays. The outcome variables for all analyses are min.day ^-1 engaged in 23 categories of behaviour in 12 locations (see Table 2.1).

Sampling took place across 14 local education authorities (LEAs), randomly drawn from the total of 32: Aberdeenshire, Dumfries and Galloway, Dundee, East Ayrshire, South Ayrshire, Edinburgh, Falkirk, Fife, Glasgow, Highland, North Lanarkshire, South Lanarkshire, Perth and Kinross, and Renfrewshire. Schools were then randomly selected from each LEA to be approached to take part in the study. Ratios of secondary to independent schools were maintained in the selection process. From www.schoolsnet.com a list of schools in each of the selected LEAs was printed before random numbers were generated and the corresponding schools selected. If a selected school had less than 300 pupils, the school was discarded for reasons of representativeness, and another randomly selected.

Schools identified were contacted by letter and invited to participate. The aims and expectations of the study were outlined and schools that agreed to take part were sent a pack including three sets of 30 diaries (approximately 75 for distribution and the rest as spares in case of loss, damage etc) and an evaluation form. Useable data were returned by 27 schools.

In Phase 1 (October-November 2002), one class from each of the Year Groups S2 (mean age=13.24 years), S3 (mean age=14.24y), and S4 (mean age=15.18y) was chosen at random by a co-ordinator at the school and each student within the chosen class was given a diary to complete in their free-time. Schools were offered the incentive of £1 for the return of each completed diary. In order to assess, and control for, possible seasonal variations in behaviour a second phase of testing was carried out six months after Phase 1 in February-May 2003. Each school that returned Phase 1 data was asked to select a second set of Year S2, S3, and S4 classes and repeat the study. It was stressed that Phase 2 classes should not include any student who had previously returned data in Phase 1. Mean ages at Phase 2 were S2=13.62 years, S3=14.55y, and S4=15.55y.

Table 2.1 Behaviours and locations assessed using EMA diaries

Of the 1056 participants who returned diaries, 60% were girls. Assuming there is an equal proportion of girls and boys in the school population, our sample reflects a gender bias beyond that expected by chance (Chi-square (X 2) = 38.64, df = 1, p < .01). Of the returned diaries, girls were also more likely to provide complete data (χ 2 (4, N = 1056) = 40.66, p = .0001). Forty participants (4%) returned diaries with completed demographic data but no diary data (i.e., partial responders) and were therefore excluded from further analyses. Partial responders were more likely to be male (χ 2 (1, N = 1056) = 22.14, p = .0001), slightly younger than full responders (13.7 vs. 14.1 y; t (1059) = -2.58, p = .01), and live in a less affluent area ( p = .001), but they did not differ by ethnicity ( p = 0.68) nor whether they found the diary harder to understand ( p = 0.57), compared to full responders. See Table 2.2 for summary data on participants.

Table 2.2 Demographic characteristics of the final sample

3. What is the prevalence of sedentary behaviour in Scottish youth?

Results for this report will address the prevalence of key sedentary behaviours and physically active pursuits, as well as descriptive summary data on these behaviours. To keep the volume of data manageable, variables were conceptualised as follows:

3.1 TV/Video viewing

Results in Table 3.1 show that half (48%) of boys watched up to 2 hours of TV per weekday with only a small minority (8%) exceeding 4 hour.day ^-1. Two hours or less is considered acceptable by the American Academy of Paediatrics (1986). Overall, boys averaged 2 hours and 7 minutes of TV viewing per weekday. Trends showed boys in Year S4 to be less likely to watch more than 2 hour.day ^-1 during the week (39%) than those in Years S3 (58.5%) and S2 (49%). Mean scores reflected this trend: Year S2=130 min.day ^-1; S3=135 min.day ^-1; S4=109 min.day ^-1.

Results in Table 3.3 show that 59% of girls watched up to 2 hours of TV per weekday with only a small minority (4%) exceeding 4 hour.day ^-1. Overall, girls averaged 1 hour and 49 minutes of TV viewing per weekday – 18 min s less than boys. Girls in Year S4 were less likely to watch more than 2 hour.day ^-1 during the week (28%) than those in Years S3 (41.5%) and S2 (45%). Mean scores reflected this with a decline in TV viewing from Year S2 (116 min.day ^-1) to S3 (109 min.day ^-1) and to S4 (98 min.day ^-1).

Prevalence estimates increased at weekends (Table 3.4) with 30% watching 2 hours or less per day and a quarter (24%) exceeding 4 hours. Average daily weekend viewing time was 2 hours and 39 minutes – 36 mins. less than boys. Trends showed girls in Year S4 to be less likely to watch more than 4 hour.day ^-1 during the weekend (17%) than those in Years S3 (29%) and S2 (26%). Mean scores reflected this with fewer minutes of TV viewing at weekends for those girls in S4 (131 min.day ^-1) compared with their younger counterparts (S2=170 min.day ^-1; S3=171 min.day ^-1).

For TV viewing data, we conclude that:

3.2 Other prevalent sedentary behaviours

TV viewing is the most prevalent leisure-time sedentary behaviour for young people. However, there are many other opportunities to be sedentary, including the use of new technologies. During the week, boys averaged 31 min.day ^-1 playing computer games (60 minutes at weekends) and a further 11.5 min.day ^-1 using the computer for other purposes. This contrasted with girls who averaged 3 minutes (7 at weekends) and 13 minutes respectively. However, many boys (43%) reported no computer game playing on weekdays and less than a quarter (20%) reported playing more than one hour per day. Boys showed minimal age trends. Other computer use was quite low with 71% of boys and 67% of girls reporting no use at all during the week. It should be noted, however, that this does not include computer-based homework.

Girls reported spending an average of 32 min.day ^-1 in motorised transport during the week, and 51 min.day ^-1 at weekends. Boys reported similar use during the week (28 min.day ^-1) but less at weekends (36 min.day ^-1) compared to girls. Only 25.5% of boys and 17% of girls spent no time in motorised transport during the week, whereas more than one-third of boys (39%) and girls (35%) spent between 30 and 60 minutes daily, with some boys (12%) and girls (15%) spending more than 1 hour in motorised transport.

Homework was also a prevalent sedentary behaviour, with boys averaging 29 min.day ^-1 during the week, and girls 39 min.day ^-1. At weekends, this gender difference was maintained with boys taking 14 and girls 26 min.day ^-1.

From the data on other prevalent sedentary behaviours, we conclude that:

• boys are significantly more attracted to playing computer games than girls, although a large minority of boys play no computer games during the week
• computer use, excluding use of computers in homework, is quite low
• use of motorised transport is quite high.

3.3 Physically active pursuits

During the week, boys (44 min.day ^-1) were markedly more active than girls (21.5 min.day ^-1) in sports and exercise, although these figures excluded school physical education. However, 38% of boys and 55% of girls reported no sports and exercise at all during the week, figures rising to 48% and 72% at weekends, respectively. The least active in sports and exercise were Year S3 girls, averaging only 17.5 min.day ^-1 during the week and 30 min.day ^-1 at weekends. No sport and exercise was reported by 57% of girls in Year S3 during the week and by 79% of girls in S4 at weekends.

Time in active transport, such as walking to school, averaged 26 min.day ^-1 during the week for boys and 30 min.day ^-1 for girls. These dropped to 14.5 and 19 min.day ^-1 respectively at weekends. Nearly one-quarter of boys (22%) took no active transport during the week, but this was much less in girls (13%).

For sports and exercise and active transport during the week in combination, boys averaged 70 min.day ^-1 of physical activity, meeting the national recommendation of one hour per day of moderate intensity physical activity on most days of the week (Biddle, Sallis, & Cavill, 1998). Girls averaged 51.5 min.day ^-1 in these two activities, with Year S3 being the least active with 46 min.day ^-1. Many boys, however, did meet the recommended 60-minute target. This was achieved by 48% during the week and 50% at weekends. But only 31% of girls achieved 60 minutes during the week and only 26% on the weekend.

From the data on physically active behaviours, we conclude that:

• boys are significantly more active than girls, confirming prior research
• there is still a sizeable minority of boys, and a majority of girls, choosing no sports and exercise
• active transport data give some signs for optimism, but coupled with the data on motorised transport, there is room for a shift to more active forms of transport
• average physical activity levels of boys, but not girls, appear to meet national recommendations.

3.4 Analyses by ethnicity

White-European ethnicity comprised 98% of the sample. Other ethnic groups are shown in Table 2.2. Conclusions concerning ethnic differences in sedentary and physically active behaviours are therefore not possible due to small sample sizes. However, the small group of young people of Asian ethnicity, in comparison to those reporting themselves to be White-European, showed, for weekday data, higher rates of TV viewing and use of active transport, but markedly less involvement in sports and exercise (4 min.day ^-1 vs. 30 ³).

³ Cohen’s d effect size = 0.89, described as ‘large’

3.5 Analyses by socio-economic status

Using deprivation categories based on participant’s postcodes, and created from the Medical Research Council’s data base⁴, we found no significant relationship between deprivation category score (1=more affluent; 7=more deprived) and the behaviours of TV viewing, active transport, or sports and exercise, for either boys or girls.

In addition, two groups were created (scores 1-3 = ‘affluent group’; 5-7 = ‘deprived group’; those with a mid-range score of 4 were excluded) to test for differences across behaviours. For males, there were no differences in TV viewing, playing computer games, active transport, or sports and exercise. However, those in the more affluent group reported greater time spent on the computer than those in the more deprived group ( p=.009). For girls, there were no differences between groups in TV viewing, playing computer games, time spent on the computer, active transport, or sports and exercise. Overall, socio-economic status was largely unrelated to the key behaviours in this sample.

We conclude that:

• ethnicity and socio-economic status have little or no effect on our data, although given the distribution of the sample by ethnicity, this finding needs to be treated with some caution.

⁴www.msoc-mrc.gla.ac.uk/Publications/pub/Carstairs_MAIN.html

5. References

American Academy of Pediatrics. (1986). Television and the family. Elk Grove Village III: American Academy of Pediatrics.

Biddle, S. J. H., Sallis, J. F., & Cavill, N. (Eds.). (1998). Young and active? Young people and health-enhancing physical activity: Evidence and implications. London: Health Education Authority.

Marshall, S. J., Biddle, S. J. H., Gorely, T., Cameron, N., & Murdey, I. (2004). Relationships between media use, body fatness and physical activity in children and youth: A meta-analysis. International Journal of Obesity, 28, 1238-1246.

Marshall, S. J., Biddle, S. J. H., Murdey, I., Gorely, T., & Cameron, N. (2003). But what are you doing now? Ecological momentary assessment of sedentary behavior among youth [abstract]. Medicine and Science in Sports and Exercise, 35(5, Suppl.), S180.