Dietary assessment and physical activity measurements toolkit

Sedentary behaviours


Sedentary behaviours may be defined as engagement in pursuits that require expending low amounts of energy i.e. >0.9 (sleeping) but <2.0 (sitting) Metabolic Equivalents (METS). It is a complex area and has been over simplified in the past (Biddle, 2007); it is not merely the absence of moderate or moderate-to-vigorous physical activity (Spanier et al, 2006; Healy et al, 2008a).  Importantly, sedentary behaviours can readily coexist with physical activity.  There is a frequent assumption in both academic circles and the media that young people are less active than in previous generations, but there is little behavioural or physiological data to support this, although a steep decline in physically active transport to school is apparent (Biddle et al, 2004).  Indeed it appears that in the last 50 years the absolute volume of sedentary behaviours undertaken by youth may have remained largely unchanged; the types of activity have changed as TV and small screen use has replaced comic books and music (Biddle, et al, 2004; Marshall et al, 2006).  There is increasing interest in sedentary behaviours as an independent health risk factor. It is also apparent that sedentary behaviours may have different correlates to physical activity and that these differ between boys and girls (Leatherdale et al, 2008). The measurement of sedentary behaviour is not a well developed field and many misconceptions exist, e.g. that television viewing is a measure of overall sedentary behaviour in youth.  In addition to the promotion of physical activity, reductions in sedenatary behaviour are rapidly becoming a public health focus.

Television viewing
There is evidence of positive, although weak, associations between children’s television viewing time and body mass index or percent body fat but few studies have examined whether these associations are independent of physical activity levels (Salmon et al, 2008). In a comprehensive review of health-enhancing physical activity in children and adolescents it was noted that most children and adolescents do not exceed recommended daily hours of TV viewing and that physical activity is unrelated to TV viewing (Biddle et al, 2004).  It appears that TV viewing accounts for less than 50% of time spent in sedentary pursuits (Gorley et al, 2007; Gorely et al 2007b).  There is virtually no evidence for the displacement hypothesis i.e. TV and other sedentary pursuits will displace more active pursuits (Sallis et al, 2000; Marshall et al, 2004; Marshall et al, 2006).  It appears that boys watch more television (or are higher users of computers) than girls (Marhsall et al, 2006). 

For adults, it may be that TV viewing is a better marker of sedentary behaviour in women than men (Sugiyama, 2008a). 

Measurement of Sedentary Behaviours
Typically, physical activity is assessed and individuals are classified according to their ‘score’ as being active or not; inactive is said to be sedentary.

There are 4 categories of sedentary behaviours, which ideally, should all be measured; the first two are the most dominant:
1. Technological (screen time)- TV, computer use (leisure), small screen use
2. Socialising – chat, phone, texts
3. Motorised transport
4. Homework (for children) or reading

Ideally, when measuring sedentary behaviour the aim is to capture accurately:

  • What was done
  • Who with - friends, family, self (social context)
  • Where - indoor, outdoor (physical environmental context)
  • The frequency of sedentary behaviours
  • The duration of sedentary behaviours

Self-report, observation, parental report and real time data capture are the main measurement tools used to assess sedentary behaviours.  Self-report can be either by questionnaire or diary.  Accelerometers which show total inactivity or the absence of physical activity do not provide the context of the behaviour.  

The structure of the questionnaire is important and recalls of activity must be broken down and time bound.  Some well known tools in the area are listed:

  • Self-Assessed Physical Activity Checklist (SAPAC) - this tool has been psychometrically tested and uses a long list of prompts (Brown et al, 2004);
  • Previous Day Physical Activity Recall (PDPAR) - designed to assess physical activity and sedentary behaviours (Pate et al, 1997; Pate et al 1999);
  • Multimedia Activity Recall for Children and Adolescents (MARCA) - a computerised 24-hour activity recall linked to a compendium of energy expenditure (Ridley et al, 2002);
  • Adolescent Sedentary Activity Questionnaire (ASAQ) - includes five categories: small screen recreation, education, travel, cultural activities and social activities (Hardy et al, 2007);

A systematic review of questionnaires which included a television assessment component has been published (Bryant et al, 2006).

Ecological Momentary Assessment (EMA) is an assessment strategy that can simultaneously capture behaviour and the factors that influence it; the method is also known as experience sampling or ambulatory diary assessment (Dunton et al, 2005). Individuals report their current activity, location, and social surroundings at any particular moment.  The method has been used in a small number of studies only, in both adults and adolescents.  In the UK, 923 adolescent girls kept pen and paper diaries of free time i.e. outside of school for three weekdays and one weekend day (Gorely et al, 2007; Gorely et al 2007b). A US study in adolescents captured this information by a Personal Device Assistant (PDA) (Dunton et al, 2005).   In the EMA diaries individuals recorded WHAT they were doing in 15 minute intervals-NOT what they had been doing in the past 15 minutes as in a typical activity diary or log. Location and details of other people present were also recorded.
 
The EMA diary method produces rich complex data, time points are aggregated and then reduced to daily summaries and typically reduced further to provide a summary of weekday and weekend behaviour. In children there is a reasonable argument for measuring time out of school, the rationale being that options to decrease sedentary behaviour in school are limited and it was what children CHOOSE to do which is important and provides a platform to intervene.  In younger children a proxy report may be used but this is problematic for parents to do as they are not there all the time. Observational methods are intrusive and may cause reactivity, but technological advances may make this method more feasible. 

Measurement of TV viewing
A systematic review of the measurement of TV viewing in children and adolescents urged researchers to consider the level of precision that is required as well as feasibility issues (Bryant et al, 2006). 

  • The ‘Robinson school based intervention self-report instrument’ (Robinson et al, 1995) had the highest reliability (r=0.94), however the test, re-test was done on the same day (Bryant et al, 2006).
  • The ‘Direct estimate of hours per week of TV’ developed by Anderson et al (1985) had the highest validation (r=0.6), and this was undertaken by comparison with a 10-day viewing diary not a criterion method of direct observation. 

Often TV viewing was assessed as a component of other questionnaires measuring either physical activity or sedentary behaviours.  The authors concluded that few of these assessment tools have supportive psychometric evidence for validity or reliability (Bryant et al, 2006). Of the ones that do, none assessed validity with a criterion measure. 

  • The measure which demonstrated the greatest reliability (r=0.98) was the PDPAR (Weston et al, 1997), again reliability was tested on the same day.  This tool also had the best validity compared to pedometer counts (r=0.88).
  • The ‘New Moves obesity prevention physical education program’ tool (Neumark-Sztainer et al, 2003) which was re-administered a month apart also had good reliability (r=0.8).

Single item tools within a survey to measure TV watching lack content validity and are subject to measurement error relating to memory and social desirability bias; estimates will be crude (Bryant et al, 2006).

Activity or viewing diaries allow more detailed information about the TV programmes to be collected and are not subject to error associated with memory.  However diaries are intrusive and may cause reactivity. 

Direct observation either by video or by researcher are considered a gold standard method for measuring TV exposure but is burdensome for researchers and is likely to affect behaviour.

Advances in accelerometry and high frequency movement sampling will contribute to the measurement of sedentary behaviour as motorised transport, for example, can be distinguished.  However there is an urgent need for the development of observational tools which are low burden for the individual and researcher. 
  
Sedentary behaviours and health risk
The Australian Diabetes, Obesity and Lifestyle Study (AusDiab) has shown that independent of time spent in moderate to vigorous intensity activity, there were significant associations of sedentary time, light intensity time and mean activity intensity with waist circumference and clustered metabolic risk (Healy et al, 2008b).  An Australian survey of over 2000 adults showed that those who spent more time in sedentary behaviours but were sufficiently physically active had a similar risk of being overweight or obese as those who were insufficiently active but spent less time in sedentary behaviour (Sugiyama et al, 2008b).  This suggests that reducing leisure time sedentary behaviours may be as important as increasing leisure time physical activity in obesity prevention. 

Observational studies of the relationship between TV viewing and health outcomes have been systematically reviewed (Williams et al, 2008).  In adults, greater amounts of TV viewing appear to be associated with overweight but the relationship with other health outcomes is not consistent (Williams et al, 2008). 

A meta-analysis of studies in children and adolescents investigated the relationships between media use, body fatness and physical activity.  A statistically significant relationship was found between TV viewing and body fatness but the magnitude was such that the clinical significance of was irrelevant (Marshall et al, 2004). In an adult prospective population cohort study in the UK, sedentary time was measured by individually calibrated heart rate monitoring.  Body mass index, fat mass and waist circumference were associated with sedentary behaviour but sedentary time was not predictive of future obesity (Ekelund et al, 2008). 

The association of TV viewing time with other sedentary behaviours has been examined in a large sample of Australian adults (Sugiyama, 2008a).  After adjustment for body mass index and socio-demographic variables, women’s TV viewing time was associated with time in other sedentary behaviours and negatively with leisure time physical activity; these associations were not present in men (Sugiyama, 2008a).

The dose response associations of television viewing have been examined in Australian adults who met the public health guideline for physical activity and a positive association with a number of metabolic risk variables was apparent; the associations were stronger in women (Healy, 2008a).

The term ‘inactivity physiology’ has been coined to describe the effect of inactivity on muscular ability (Hamilton et al, 2007).  The potential role of low energy expenditure and sitting in obesity, metabolic syndrome, Type 2 diabetes and cardiovascular disease has been reviewed (Hamilton et al, 2007).  In society today, prolonged sitting time is commonplace for many people who spend their working days largely sitting, and for old people in nursing homes or at home.  The benefits in terms of metabolic risk in breaking up sedentary time have been shown (Healy et al, 2008c).

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