sedentary behaviour
Majority of our lives spent in NEAT
-Because NEAT is likely to be the *largest component of activity thermogenesis* - we spend the majority of our lives in this state - it reminds us that* energy expended during activities* of daily living can be extremely important for *maintaining caloric balance*.
objectives
-Define and differentiate sedentary behaviour, physical inactivity and physical activity. -Discuss health implications associated with a sedentary lifestyle -Highlight some of the health benefits of interrupting (breaking up) sedentary time with bouts of standing and light-intensity physical activity, and MVPA
Over the past decade, a growing body of epidemiological evidence indicates that sedentary time is associated with:
-Metabolic syndrome -Cardiovascular disease -Type 2 diabetes -Cancer -All-cause mortality -Depression -Anxiety
NEAT (Non-excercise activity thermogenesis) definition
-NEAT includes the energy expenditure associated with posture allocation (e.g., sitting, standing, and lying), fidgeting, and routine daily movements such as walking and performing household chores -NEAT can be thought of as energy expenditure associated with sedentary behaviour and light activity.
SUMMARIES/ Take away points
-Sedentary behaviour is not the same thing as "physical inactivity" -Sedentary behaviour poses unique health consequences, independent of MVPA (although more research is needed) -Some of the physiological responses induced by sedentary behaviour are unique and are associated with adverse health outcomes
researching is showing that there are connections (adverse) but the strength of the evidence is not yet strong enough. focus on: -depression -cardiovascular disease -anxiety
-Self report methods, etc -evidence basis limited to cross-sectional studies. -large groups of people for short period of times -longitudinal studies, etc.s
lipoprotein lipase (LPL)
-The deleterious effects of sedentary behaviour on metabolic health appear to be at least partially mediated by changes in lipoprotein lipase (LPL) activity. -LPL is an enzyme that facilitates uptake of free fatty acids into skeletal muscle and adipose tissue
3 types of sedentary behaviours
1. Domestic 2. Occupational 3. Transportation
Two differing definitions of *sedentary behaviour* (not in common language)
1. defines sedentary behaviour only by intensity, specifically, "any waking behaviour or activity engendering <=1.5 metabolic equivalents (METs) 2. "any waking behaviour characterized by an energy expenditure of <= 1.5 METs while in a sitting or reclining posture
exercise
A subset of physical activity that is planned, structured, repetitive bodily movement done to improve or maintain one or more components of physical fitness
Physical Inactivity
"inactive" be used to describe those who are performing insufficient amounts of MVPA (i.e., not meeting specified physical activity guidelines -findings from the *sedentary behaviour research* sedentary and inactive are separate concepts
Similar findings have also shown LPL activity to be reduced in response to sedentary behaviour in humans
(1998) examined the effects of 11 days of bed rest among healthy Japanese subjects. Subjects displayed an 18% decrease in LPL activity, accompanied by significant increases in plasma triglycerides and decreases in HDL cholesterol...
Limited evidence indicates that sedentary behaviour may also have deleterious effects on vascular health...
(2007) examined changes in vascular function following 5 days of bed rest in 20 healthy subjects. Peripheral vascular function was reduced by ~20% in the legs and ~30% in the arms following a bed rest protocol Subjects experienced an increase in blood pressure and significant decrease in brachial artery diameter
Sedentary Behaviour and Psychosocial Health (TV Exposure)
In 1971, the average age at which children began to watch TV was 4 years...today it is 5 months! Currently, an estimated 90% of children begin watching TV before age 2, in spite of recommendations to the contrary Exposure to TV before 3 years has been shown to have detrimental effects on attention, language, cognitive development, reading recognition, comprehension, and memory
Low levels of LPL are associated with:
Increased circulating triglyceride levels Decreased HDL cholesterol Increased risk of cardiovascular disease
Differences in METs values between: -sedentary behaviour -Physical Inactivity -Physical Activity
Light (1.5-3.0 METs) Moderate (3.0-6.0 METs) Vigorous (>6 METs
SB and Adverse Heath Outcomes Link
Links between sedentary behaviour and adverse health outcomes were noted as early as the 17th century by Italian physician *Bernadino Ramazzini* Studied needle workers and noted the relationship between occupational-related sedentary behaviour and deteriorating health.
Morris' Transport wokers findings
Men in more sedentary occupations such as bus drivers and civil servants had higher mortality rates from coronary heart disease compared to more active bus conductors and postal workers
Physiological Implications: Recent evidence suggests that sedentary behaviour has a direct influence on
Metabolism Bone mineral content Vascular health
National Institutes of Health-American Association of Retired Persons Diet and Health Study
Prospective cohort of 488,720 men and women aged 50-71 from 1995-1996 High levels of TV and/or video watching were associated with wan increased risk of colon cancer for men and women and endometrial cancer in women Women who spent >7 hours/day sitting had an increased risk of endometrial cancer compared with those who sat <3 hours/day
How active and sedentary are *Canadians*
Results from the 2012 and 2013 surveys indicate that: Canadian adults aged 18 to 79 spent on average a total of 4 hours and 11 minutes per day being physically active. Of the time spent being active, the majority was spent in light activity (3 hours and 46 minutes), and the remaining time in moderate-to-vigorous activity (MVPA) (25 minutes) (Chart 1). Out of those 25 minutes of MVPA, 12 minutes were done in periods of at least 10 minutes (data not shown). On average, adults spent 9 hours and 48 minutes of their waking time being sedentary. Total daily sedentary time was higher in older age groups. Adults aged 18 to 39 were sedentary for 9 hours 36 minutes. Adults aged 40 to 59 were sedentary for 9 hours and 49 minutes. Older adults aged 60 to 79 were sedentary for 10 hours and 8 minutes daily.
Domestic
TV watching and other screen-based sedentary time
Adults
The relationship between sedentary behaviour and psychosocial outcomes has been less studied in adults... A prospective cohort study of Spanish university students found that the odds of having a mental disorder was 31% higher for subjects spending more than 42 hours/week watching TV compared to adults watching less than 10.5 hours/week
LPL activity appears to be reduced in response to both:
acute and chronic sedentary behaviour
Findings: Sedentary time increases risk for chronic disease and mortality independent of physical activity (2012)
compared the effects of 7 h of uninterrupted sitting with sitting interrupted by short 2-min bouts of light intensity walking (~3.2 km/h) every 20 min for 5 h. Breaking up sedentary time led to a 24%-30% reduction in postprandial plasma glucose and a 23% reduction in circulating insulin.
Occupational
desk/computer-based work
Findings: Sedentary time increases risk for chronic disease and mortality independent of physical activity. (2009)
examined 240,819 U.S. adults (aged 50-71) and found that those who reported >7 h/week of MVPA but who also reported >7 h/week of TV watching had a 50% greater risk of death from CVD compared to people who undertook the same amount of MVPA but watched <1 h of TV per week.
Findings: Sedentary time increases risk for chronic disease and mortality independent of physical activity (2008)
examined the effects of breaking up sedentary time on biological markers of metabolic risk and found that more frequent interruptions were beneficially associated with waist circumference, BMI, triglycerides, and 2-h plasma glucose.
Findings: Sedentary time increases risk for chronic disease and mortality independent of physical activity. (2014)
examined the relationship between accelerometer-derived sedentary time and cardiometabolic biomarkers in 4,935 Canadian adults (aged 20-79) and found that both total sedentary time and sedentary bouts lasting >20 minutes were associated with higher insulin and lower diastolic blood pressure, independent of MVPA.
Findings: Sedentary time increases risk for chronic disease and mortality independent of physical activity. (2012)
examined the relationships between sitting time and mortality in 17,000 Canadian adults (aged 18-90) and found that higher volumes of daily sitting time was associated with increased all-cause mortality and cardiovascular disease risk, even after statistically controlling for factors such as age, sex, smoking, alcohol consumption, and leisure-time PA
Transportation
sitting in a car or bus
Health Benefits of Standing vs. Sitting
An emerging (but controversial) body of research also suggests that greater time spent standing is related to improvements in postprandial glucose response and lower risk of cardiovascular disease and all-cause mortality. (2014) study examined associations between daily standing time and mortality in 16,586 Canadian adults aged 18-90 and found that those who reported standing up for most of the day had a 33% lower risk of dying than those who reported standing almost none of the time.
PA
Any bodily movement produced by skeletal muscles that results in energy expenditure
Sedentary behaviour has been linked with metabolic dysfunctioon
Characterized by increased plasma triglyceride levels, decreased levels of high-density lipoprotein (HDL) cholesterol, and decreased insulin sensitivity
20th century advances in SB
Dr. *Jeremy Morris* studied London transport workers and British civil servants (1949 and 1950) and examined the incidence of coronary artery disease in 31,000 middle-aged men according to activity level.
2003 Rat Skeletal muscles and LPL hind limb unloading
Employed hind limb unloading to examine the influence of sedentary behaviour on LPL activity in rats. Intracellular LPL activity in lower limbs skeletal muscle was reduced by more than 25% after just 6 hrs. and continued to decrease in a dose-response fashion with an approximate 75% reduction in LPL activity after 18 hrs. Interestingly, it took just 4 hrs. of light-intensity walking and normal cage activity to return LPL activity in lower limbs to baseline levels...
unclear whether reported changes in vascular function following bed rest are due to sedentary behaviour or to the postural conditions imposed on subjects.
However, given the dramatic changes in vascular function observed by (2007), who did not use a micro-gravity protocol, it appears that sedentary behaviour is likely to have at least some direct influence on vascular health...
