2) Seddentary Behaviour

What is sedentary behaviour

Any waking behaviour involving very low energy expenditure (1-1.5 METs) that occurs while sitting or reclining

What are the 2 defining characteristics of sedentary behaviour

• very low energy expenditure: 1-1.5 METs

• Occurs while sitting or reclining during waking hours

Is sedentary behaviour the same as physical inactivity

NO

• Sedentary behaviour = low-energy behaviours while sitting/reclining

• Physical inactivity = not doing enough moderate/vigorous activity

What are the main recommendations for sedentary behaviour

• Limit the amount of time being sedentary

• Replace sedentary time with more PA

What is the key principle for reducing sedentary behaviour

• Don’t just focus on adding exercise

• Reduce sitting/sedentary time and replace it with movement

How does reducing sitting time affect life expectancy

Reducing sitting time to < 3 hours/day is associated with living approximately 2 years longer

How does reducing television viewing affect life expectancy?

Reducing television viewing to <2 hours/day is associated with living approximately 1.38 years longer (Katzmarzyk et al., 2012).

How does sitting time relate to heart disease risk?

For all-cause mortality, sitting for up to 8 hours/day was associated with approximately a 1% increase in heart-disease risk per additional hour of sitting.

Why should television viewing be considered separately from total sedentary time?

TV viewing can cluster with other unhealthy behaviours, such as poor diet, which may contribute to negative health outcomes.

What health-related outcomes can be negatively associated with sedentary behaviour

Reductions in:

• health-related quality of life

• cognitive function

• PA levels

• physical functioning

Increased risk/association with:

• dementia

• depression

• function and disability

What sedentary behaviours are commonly examined in relation to health?

• Total sedentary behaviour (SB)

• television viewing

What can reducing or breaking up sedentary behaviour improve

• Body composition

• Cardiometabolic risk

• Cognitive function, particularly in relation to computer/internet use

Why might breaking up sedentary behaviour be beneficial

Interrupting prolonged sitting with movement may reduce some of the negative physiological effects associated with extended sedentary periods

What is a systematic review

A study that systematically compiles existing research using defined criteria/parameters to determine whether a variable is associated with an outcome

What is a meta-analysis

A statistical method used within systematic reviews to combine results from multiple studies and estimate an overall effect

What was the relationship between sitting time and heart disease/diabetes risk?

People who spent more time sitting each day had:

• 29% increased risk of developing heart disease

• 13% increased risk of developing diabetes

The increased risk remained after accounting for PA

• 11% increased risk of diabetes

• 14% increased risk of heart disease

The relationship between sedentary behaviour and disease risk cannot be explained entirely by physical activity levels.

What is a hazard ratio (HR)

A measure comparing the probability/rate of an outcome occurring between 2 groups, such as high vs low sedentary behaviour groups

What does HR = 1 mean

No difference in risk/rate between the groups

What does HR > 1 mean

The outcome is more likely/higher in the exposed group

What does HR < 1 mean

The outcome is less likely/lower in the exposed group

What is an “active couch potato”

Someone who meets PA recommendations or exercises regularly but still spends large amounts of time sedentary

Does PA completely eliminate the risks of sedentary behaviour

NO

• PA can negate some, but not all, of the risk associated with sedentary behaviour

Who experiences stronger effects from sedentary behaviour

People who are less physically active

How does physical inactivity affect all-cause mortality risk compared with high PA

• Physically inactive: 46% higher risk of all-cause mortality

• Highly physically active: 16% higher risk

What does the “active couch potato” concept suggest about PA

Being PA does not completely compensate for prolonged sedentary behaviour

Do highly sedentary people need more physical activity to achieve the same mortality risk as less sedentary people?

Yes. Highly sedentary people need more physical activity to achieve the same level of absolute mortality risk as people who are less sedentary.

What physiological problems can result from prolonged sedentary behaviour?

Sedentary behaviour affects cardiovascular, metabolic, and fitness outcomes.

Effect	Meaning
Impaired vascular function	Reduced functioning of blood vessels
↑ Blood pressure	Greater cardiovascular strain
Impaired insulin sensitivity	Reduced ability to respond effectively to insulin
Weight gain	Increased body weight/body fat
↑ Blood lipids	Less favourable blood-fat profile
↓ Cardiorespiratory fitness	Reduced ability to use oxygen during activity

What is a sedentary bout

A period of uninterrupted sedentary behaviour

What is a sedentary break

A non-sedentary period occurring between 2 periods of sedentary behaviour

Why might we want to break up sedentary behaviour

To reduce prolonged periods of sitting and potentially reduce some negative health effects

What is an example of breaking up sedentary behaviour

Standing up and moving around periodically during extended sitting.

How does breaking up sedentary behaviour relate to the "active couch potato" concept?

• Someone may go to the gym but remain sedentary for most of the day.

• Breaking up sitting throughout the day may therefore be important in addition to planned exercise

Is there strong evidence for the health effects of sedentary bouts/breaks?

Insufficient evidence

• conclusions about the effects of specific bouts/breaks should be interpreted cautiously.

What is the median total sitting time across studies?

8.1 hours/day.

How much sedentary time do children aged 2–6 years spend sitting?

4.4 hours/day.

How much sedentary time do adolescents aged 12–18 years spend sitting?

9.3 hours/day.

What is the sedentary behaviour guideline for recreational screen time in children and youth?

<2 hours/day of recreational screen time.

What is the average screen time reported in the notes?

2.9 hours/day, with a range of 1.6–5.6 hours/day.

How much time do children spend in sedentary pursuits after school?

Approximately 41–51% of children spend most of their after-school time in sedentary pursuits.

How much time do adolescents spend in sedentary pursuits after school?

Approximately 57% spend most of their after-school time in sedentary pursuits.

How does objectively measured sitting compare with self-reported sitting in adults?

More sitting is observed through objective measurement than is reported through self-report, suggesting that people may underestimate their sedentary time

What is a correlate

A factor associated with a particular behaviour

Does a correlate necessarily cause a behaviour?

NO

• Correlation/association does not necessarily mean causation.

Give an example of a correlate of sedentary behaviour.

AGE

• as people get older, they tend to become more sedentary

Why is it important to distinguish correlates from causes?

An association between two factors does not prove that one causes the other

What objective measures can be used to measure sedentary behaviour?

• Accelerometer — e.g., ActiGraph

• Posture monitor — e.g., activPAL

• Wearable technology — e.g., Fitbit

• Pedometers

Why are posture monitors particularly useful for sedentary behaviour?

They can provide information about body position/posture, helping distinguish sitting/reclining from other types of movement.

What subjective/self-report methods can measure sedentary behaviour?

• Questionnaires

• Interviews

• Time-use diaries

• Proxy reporting

What is an example of proxy reporting for sedentary behaviour?

A parent reporting a child’s TV viewing time

What are major problems with self-reported sedentary behaviour?

• Recall bias

• Reporting bias

• People may underestimate sedentary time

• People may over-report PA

What are the main advantages of objective measures of sedentary behaviour?

• More direct/objective

• Less dependent on memory

• Can capture patterns of movement/sitting

• Useful for identifying sedentary bouts and breaks

What are disadvantages of objective measures

• Can be expensive

• May be burdensome to wear

• May require technical expertise/data processing

• Different devuces may measure behaviour differently

What are the advantages of self-report measures

• Cheap

• Easy to administer

• Practical for large populations

• Can capture contextual information that devices may miss

What are the disadvantages of self-report measures?

• Recall bias

• Reporting/social-desirability bias

• Can misestimate sedentary time

• People may underestimate sitting and over-report activity