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Too Much Sitting: The Population Health Science
of Sedentary Behavior
Neville Owen
1,2
, Genevie` ve N. Healy
1,2
, Charles E. Matthews
3
, and David W. Dunstan
2
1
The University of Queensland, School of Population Health, Cancer Prevention Research Centre, Brisbane,
Australia;
2
Baker IDI Heart and Diabetes Institute, Melbourne, Australia; and
3
Nutritional Epidemiology Branch,
Division of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville, MD
OWEN, N., G.N. HEALY, C.E. MATTHEWS, and D.W. DUNSTAN. Too much sitting: the population health science of
sedentary behavior. Exerc. Sport Sci. Rev., Vol. 38, No. 3, pp. 105Y113, 2010. Even when adults meet physical activity guidelines,
sitting for prolonged periods can compromise metabolic health. Television (TV) time and objective measurement studies show deleterious
associations, and breaking up sedentary time is beneficial. Sitting time, TV time, and time sitting in automobiles increase premature
mortality risk. Further evidence from prospective studies, intervention trials, and population-based behavioral studies is required.
Key Words: environmental and social change, TV time, breaks in sedentary time, accelerometer measurement, blood glucose,
triglycerides, metabolic health
Editor’s Note: This Perspectives for Progress article is
based on the corresponding author’s President’s Lecture from the
American College of Sports Medicine’s 56th Annual Meeting held
in May 2009.
INTRODUCTION
The physical, economic, and social environments in which
modern humans sit or move within the contexts of their
daily lives have been changing rapidly, and particularly so
since the middle of the last century. These changes Vin
transportation, communications, workplace, and domestic
entertainment technologies Vhave been associated with
significantly reduced demands for physical activity. However,
these reductions in the environmental demands for being
physically active are associated with another class of health-
related behaviors.
Sedentary behaviors (typically in the contexts of television
(TV) viewing, computer and game console use, workplace
sitting, and time spent in automobiles) have emerged as a
new focus for research on physical activity and health
(18,27,31Y33). Put simply, the perspective that we propose is
that too much sitting is distinct from too little exercise. Research
findings on sedentary behavior and health have proliferated
in the 10 yr after publication of our first Exercise and Sport
Sciences Reviews article on this topic (32). As we will dem-
onstrate, initial findings on the metabolic correlates of pro-
longed TV viewing time have since been confirmed by recent
objective measurement studies, which also show that breaking
up sedentary time can be beneficial. Furthermore, we describe
recent studies from Canada, Australia, and the United States,
which show prospective relationships of sedentary behaviors
with premature mortality. Importantly, adults can meet public
health guidelines on physical activity, but if they sit for pro-
longed periods, their metabolic health is compromised. This is
a new and challenging area for exercise science, behavioral
science, and population health research. However, many sci-
entific questions remain to be answered before it can be con-
cluded with a high degree of certainty that these adverse health
consequences are uniquely caused by too much sitting,orifwhat
has been observed so far can be accounted for by too little light,
moderate, and/or vigorous activity.
The updated recommendation for adults on Physical Activity
and Public Health from the American College of Sports Medi-
cine and the American Heart Association (ACSM/AHA)
clearly states that ‘‘the recommended amount of aerobic
activity (whether of moderate or vigorous intensity) is in
addition to routine activities of daily living, which are of light
intensity, such as self-care, casual walking, or grocery shopping,
or less than 10 min of duration such as walking to the parking
105
PERSPECTIVES FOR PROGRESS
Address for correspondence: Neville Owen, Ph.D., The University of Queensland,
Cancer Prevention Research Centre, School of Population Health, Level 3, Public
Health Bldg., Herston Rd., Herston QLD 4006, Australia
(E-mail: n.owen@sph.uq.edu.au).
Accepted for publication: March 23, 2010.
Associate Editor: Priscilla M. Clarkson, Ph.D., FACSM
0091-6331/3803/105Y113
Exercise and Sport Sciences Reviews
Copyright *2010 by the American College of Sports Medicine
Copyright @ 2010 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
lot or taking out the trash’’ ((20), p. 1426). Logically, doing
such daily activities differently could involve reductions in
sitting time, but sitting per se is not addressed specifically in the
recommendations. In this context, the key question to be asked
about the strength of the evidence on sedentary behavior and
health that we present in this article is: Would one expect to
see a statement on reducing sitting time included in future
physical activity recommendations?
Sedentary Behavior
Sedentary behaviors (from the Latin sedere, ‘‘to sit’’) in-
clude sitting during commuting, in the workplace, the
domestic environment, and during leisure time. Sedentary
behaviors such as TV viewing, computer use, or sitting in
an automobile typically are in the energy expenditure range
of 1.0Y1.5 METs (multiples of the basal metabolic rate) (1).
Thus, sedentary behaviors are those that involve sitting and
low levels of energy expenditure. In contrast, moderate- to
vigorous-intensity physical activities such as bicycling, swim-
ming, walking, or running may be done in a variety of body
positions, but require an energy expenditure of 3Y8 METs (1).
In this perspective, light-intensity activity behaviors are
those done while standing that require an expenditure of no
more than 2.9 METs.
Addressing research on the health consequences of seden-
tary behavior requires some initial clarification of terminol-
ogy. We refer to sedentary behaviors (different activities for
different purposes in different contexts; see previous descrip-
tion). We also refer to sitting time, a generic descriptor cov-
ering what these sedentary behaviors primarily involve. As
we demonstrate later, adults spend most of their waking
hours either sitting or in light-intensity activity (predominantly
standing with some gentle ambulation).
Time in sedentary behaviors is significant, if only because
it displaces time spent in higher-intensity physical activity V
contributing to a reduction in overall physical activity en-
ergy expenditure. For example, displacement of 2 hId
j1
of
light-intensity activity (2.5 METs) by sedentary behaviors
(1.5 METs) would be predicted to reduce physical activ-
ity energy expenditure by about 2 MET-hId
j1
or approxi-
mately the level of expenditure associated with walking for
30 minId
j1
(0.5 h * 3.5 METs = 1.75 MET-h).
Research on physical activity and health has concentrated
largely on quantifying the amount of time spent in activities
involving levels of energy expenditure of 3 METs or more,
characterizing those with no participation at this level as
‘‘sedentary’’ (33). However, this definition neglects the sub-
stantial contribution that light-intensity activities make to
overall daily energy expenditure (8) and also the potential
health benefits of participating in these light-intensity activ-
ities, rather than sitting. Furthermore, although individuals
can be both sedentary and physically inactive, there is also the
potential for high sedentary time and physical activity to
coexist (the Active Couch Potato phenomenon, which we will
explain later). An example would be an office worker who
jogs or bikes to and from work, but who then sits all day at a
desk and spends several hours watching TV in the evening.
Common behaviors in which humans now spend so much
time VTV viewing, computer use and electronic games,
sitting in automobiles Vinvolve prolonged periods of low-
level metabolic energy expenditure. It is our contention that
sedentary behavior is not simply the absence of moderate- to
vigorous-intensity physical activities, but rather, is a unique
set of behaviors with unique environmental determinants and
a range of potentially unique health consequences (43). Our
population health research perspective is on the distinct role
of sedentary behavior, as it may influence obesity and other
metabolic precursors of major chronic diseases (type 2 dia-
betes, cardiovascular disease, and breast and colon cancers).
Sedentary Behavior and Health: A Unique
Underlying Biology?
Physiologically, distinct effects are observed between pro-
longed sedentary time and too little physical activity (17).
There are broad consistencies between the patterns of find-
ings from epidemiological studies on the cardiometabolic
correlates of prolonged sitting that we will describe, and re-
cent evidence on biological mechanisms (‘‘inactivity phys-
iology’’) identified in animal models. It seems likely that there
is a unique physiology of sedentary time, within which bio-
logical processes that are distinct from traditionally under-
stood exercise physiology are operating. The groundbreaking
work of Hamilton and colleagues (3,16) provides a compel-
ling body of evidence that the chronic unbroken periods of
muscular unloading associated with prolonged sedentary time
may have deleterious biological consequences. Physiologi-
cally, it has been suggested that the loss of local contractile
stimulation induced through sitting leads to both the sup-
pression of skeletal muscle lipoprotein lipase (LPL) activity
(which is necessary for triglyceride uptake and high-density
lipoprotein (HDL) cholesterol production) and reduced glu-
cose uptake (3,16). A detailed account of findings and
implications from the studies of Hamilton et al. (17,18) has
been provided in recent reviews.
Findings by Hamilton et al. (17,18) suggest that standing,
which involves isometric contraction of the antigravity
(postural) muscles and only low levels of energy expenditure,
elicits electromyographic and skeletal muscle LPL changes.
However, in the past, this form of standing would be con-
strued as a ‘‘sedentary behavior’’ because of the limited
amount of bodily movement and energy expenditure entailed.
This highlights the need for an evolution of the definitions
used for sedentary behavior research. Within this perspective,
standing would not be a sedentary activity, and our approach
(subject to revision as further findings accumulate) is to
equate ‘‘sedentary’’ with ‘‘sitting.’’
THE METABOLIC HEALTH CONSEQUENCES OF TOO
MUCH SITTING
TV Viewing Time: The AusDiab Studies
The Australian Diabetes, Obesity and Lifestyle Study
(AusDiab) was conducted initially in 1999/2000 on a com-
mon leisure time sedentary behavior VTV viewing time
(TV time) Vwith biomarkers of cardiometabolic risk. AusDiab
recruited a large population-based sample of some 11,000
adults from all Australian states and the Northern Territory.
Some of our first AusDiab findings were that among adults
without known diabetes, self-reported TV time was positively
106 Exercise and Sport Sciences Reviews www.acsm-essr.org
Copyright @ 2010 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
associated with undiagnosed abnormal glucose metabolism
(12) and the metabolic syndrome (11). The strongest re-
lationships were observed in the highest TV time category
(4 hId
j1
or more). When TV time was considered as a con-
tinuous measure (10), a detrimental dose-response association
was observed in women between TV time and 2-h plasma
glucose and fasting insulin. Importantly, all of these asso-
ciations persisted after adjustment for sustained moderate-
to vigorous-intensity leisure time physical activity and waist
circumference. Some of these cross-sectional relationships have
been replicated recently in prospective analyses: increases in
TV viewing during 5 yr predicted significant adverse changes
in waist circumference for men and women and in diastolic
blood pressure and a clustered cardiometabolic risk score for
women. These associations were independent of baseline TV
time, baseline physical activity and physical activity change,
and other potential confounders (48).
Being Sedentary and Meeting Physical Activity
Guidelines: The Active Couch Potato
We further examined relationships of TV time with con-
tinuous metabolic risk in men and women who reported at
least 150 minIwk
j1
of moderate- to vigorous-intensity phys-
ical activity Vthe generally accepted public health guide-
lines for health-enhancing physical activity (20). Among
these healthy physically active adults, significant detrimental
dose-response associations of TV time were observed with
waist circumference, systolic blood pressure, and 2-h plasma
glucose in both men and women, as well as fasting plasma
glucose, triglycerides, and HDL cholesterol in women only
(23). This observation Vthe Active Couch Potato phenom-
enon Vis important. The particular metabolic consequences
of time spent watching TV are adverse, even among those
considered to be sufficiently physically active to reduce their
chronic disease risk. This finding reinforces the potential
importance of the deleterious health consequences of pro-
longed sitting time, which may be independent of the pro-
tective effect of regular moderate-intensity physical activity.
TV Viewing Time: Associations With Biomarkers
for Men and for Women
One of the striking findings in the AusDiab TV time
studies was that the associations with cardiometabolic bio-
markers were stronger for women than for men (10Y12,23).
We subsequently examined the associations of both TV time
and self-reported overall sitting time with these biomarkers in
the 2004/2005 AusDiab sample (42). The TV time relation-
ships for women were replicated, but for self-reported overall
sitting time (which is inclusive of the TV time component),
the associations were similar for men and women. So, the
question remains as to whether there is a particular relation-
ship of TV time with metabolic health for women. There are
some testable hypotheses that can be put forward in this
context: Are there dietary or TV timeYrelated snacking dif-
ferences between men and women? Are women (who have
a lower average skeletal muscle mass and a higher average
fat mass than men) metabolically more susceptible to the
adverse influences of prolonged sitting after a typically large
evening meal?
Although some of our most striking initial findings on the
adverse health consequences of sedentary behavior have been
for TV time, there should be caution in treating this common
leisure time sedentary behavior as a marker for overall sed-
entary time. We have modest evidence (39) that for women,
TV time is positively correlated with other leisure time sed-
entary behaviors and with being less likely to meet physical
activity and health guidelines. However, these findings need
to be replicated in other populations and with other measures.
Furthermore, TV viewing is associated with other health-
related behaviors (51), and those in the highest TV time
categories are more likely to eat in front of the TV set (26).
It is thus plausible that TV time will influence energy bal-
ance in two main ways. Most people sit to watch TV, and it
has a lower energy cost than the alternative activities that
it replaces. In addition, high levels of TV time are likely
to increase energy intake because of prompts from frequent
commercials about food and beverages, and unlike for many
other activities, the hands are free to eat during TV time (51).
It is thus a reasonable hypothesis that this latter factor
may partially explain why higher levels of TV time are asso-
ciated with higher waist circumferences and with adverse
blood glucose and lipid profiles.
We must emphasize that TV time is one of a number of
sedentary behaviors that characterize how adults go about
their daily lives, and there is potential measurement error
associated with using the self-report measures that are com-
mon to most TV time studies. However, based on our recent
systematic review (6), we have some confidence that the
TV time measures that we have used are reasonably reliable
and valid.
OBJECTIVE ASSESSMENT OF SEDENTARY TIME:
NEW FINDINGS
Advances in the Objective Measurement of
Sedentary Behavior
These Australian studies previously summarized have all
relied on self-reported TV time or overall sitting time. How-
ever, advances in measurement technology now provide sig-
nificantly enhanced scientific traction, which is helping to
deal with the methodological limitation of measurement
error related to the use of self-report items. Before summariz-
ing findings from our objective measurement studies with
AusDiab study participants, it is helpful to consider the new
perspectives that emerge when accelerometer data on seden-
tary time and physical activity are examined. Accelerometers
(as distinct from pedometers that count and display the
number of steps taken) are small electronic devices worn on
the hip that provide an objective record of the volume,
intensity, and frequency of activity between and within days,
which may be downloaded to computer databases and used
to derive scientifically meaningful activity variables. Accel-
erometers have been used as part of the National Health and
Nutrition Examination Survey (NHANES), gathering data
from large population-based samples of adult residents of
the United States. Findings reported to date suggest that
compared with what has been assumed to be the case from
self-report surveys, levels of participation in moderate- to
Volume 38 cNumber 3 cJuly 2010 Science of Sedentary Behavior 107
Copyright @ 2010 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
vigorous-intensity physical activities are extremely low (44),
and that some 60% or more of these adults’ waking hours are
spent sedentary (29).
Sedentary Behavior During Adults’ Waking Hours
To illustrate the overall patterns of activity in adults’ daily
lives, Figure 1 shows a cluster heat map (50). This is a graphic
representation from Genevieve Healy, showing accelerome-
ter data for one individual during 1 wk, in the manner origi-
nally presented by Foulis et al. (15). The values taken by the
accelerometer counts within each minute are represented
as colors in the two-dimensional map. The dark blue shading
shows accelerometer counts that are less than the currently
used, but still debated, cutoff of 100 counts per min for sed-
entary time, and which are taken to be indicative predom-
inantly of sitting (a caveat, however, is that some of the
minutes shown as sedentary will include standing quite still).
The pale blue through yellow colorings indicate light-intensity
to moderate-intensity physical activities. The yellow through
red colorings indicate moderate- to vigorous-intensity phys-
ical activity. From an energy expenditure perspective, the
dark blue translates to very low levels of energy expenditure,
with the red reflecting high energy expenditure levels. What
is striking in Figure 1 is the extent to which this person
spends his or her time either in light-intensity activities (pale
blue to white) and being sedentary (dark blue). Although we
would not contend that this is a totally precise and unam-
biguous representation of sitting time and light-, moderate-,
and vigorous-intensity activities, it nevertheless is an infor-
mative perspective.
Figure 1 illustrates one of our key messages about the role of
sedentary time in the physical activity and health equation:
it is possible to achieve a level of activity consistent with the
public health guidelines for health-related physical activity
(30 min of moderate-intensity physical activity on most days
of the week) but to spend most of waking hours involved
in sedentary behaviors. In this case, we see that the accumu-
lated moderate- to vigorous-intensity physical activity time is
31 min; however, this person spends 71% of his or her waking
hours in sedentary time. Thus, it is possible for individuals
to be physically active, yet highly sedentary Vthe Active
Couch Potato phenomenon identified in the AusDiab TV
time studies (24).
The main scientific caveat for this perspective is that
these data show ‘‘activity,’’ which we infer is reflective of
‘‘behavior.’’ However, there are scientific devils in the details
of these objective movement data. Debate remains about
what are the most appropriate activity count cut points to
identify sedentary and light-intensity activity time; also, dif-
ferent cut points may be appropriate for adults of different
ages, race/ethnicity, and adiposity status.
Objectively Assessed Sedentary Time: Key Studies
As well as demonstrating remarkably low levels of physical
activity and high levels of sedentary time within contem-
porary human environments (29,44), objective measures also
have demonstrated the adverse impact of prolonged sedentary
time on cardiometabolic biomarkers of risk. At least three
studies in Europe and Australia have examined the associa-
tions of objectively measured sedentary time with continuous
cardiometabolic biomarkers: the ProActive trial conducted
in the United Kingdom (UK), the European RISC study, and
the AusDiab study (2,13,14,23,25). For those in the UK
ProActive trial (258 participants aged 30Y50 yr with a family
history of type 2 diabetes), sedentary time was detrimentally
associated with insulin in the cross-sectional analysis (14) but
was of borderline statistical significance (P= 0.07) in the 1-yr
prospective analysis (13). Detrimental cross-sectional associ-
ations of sedentary time with insulin also were observed in
participants of the European RISC study (801 healthy par-
ticipants aged 30Y60 yr), although the associations were
attenuated after adjustment for total activity (2). In the
AusDiab accelerometer study sample (169 participants aged
30Y87 yr, general population), we observed detrimental as-
sociations of sedentary time with waist circumference, trigly-
ceride levels, and 2-h plasma glucose (22,24). It is important
to point out that the participants in all of these studies were
primarily white adults of European descent (2,13,14,22,24).
A key next step for this research is to examine whether
the associations are consistent across different racial/ethnic
groups, which is becoming feasible with the public availability
of large multiethnic population-based data sets, particularly
NHANES (29,44).
Objectively Assessed Sedentary Behavior:
AusDiab Findings
We used accelerometers to assess sedentary time in a sub-
sample of the AusDiab study participants. Sedentary time was
defined as accelerometer counts less than 100 per minute
(previously described) and was associated with a larger waist
circumference and more adverse 2-h plasma glucose and tri-
glyceride profiles, as well as a clustered metabolic risk score
(22,24). The associations of sedentary time with these bio-
markers (with the exception of triglyceride levels) remained
Figure 1. Being physically active, but also highly sedentary: 1 wk of
accelerometer count data showing, on average, 31 minId
j1
moderate- to
vigorous-intensity activity time (91951 counts per minute) and 71% of
waking hours sedentary (G100 counts per minute).
108 Exercise and Sport Sciences Reviews www.acsm-essr.org
Copyright @ 2010 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
significant after adjustment for time spent in moderate- to
vigorous-intensity physical activities (22,24).
As logically would be expected, sedentary time and light-
intensity activity time were highly negatively correlated
(r=j0.96); more time spent in light-intensity activity is
associated with less time spent sedentary. This suggests that
it may be a feasible approach to promote light-intensity
activities as a way of ameliorating the deleterious health
consequences of sedentary time. Our evidence suggests that
having a positive light-intensity activity/sedentary time bal-
ance (i.e., spending more time in light-intensity activity than
sedentary time) is desirable because light-intensity activity
has an inverse linear relationship with a number of cardio-
metabolic biomarkers (22,24).
Breaks in Sedentary Time: AusDiab Findings
One of the intriguing findings from our accelerometer
measurement studies is that breaks in sedentary time (as dis-
tinct from the overall volume of time spent being sedentary)
were shown to have beneficial associations with metabolic
biomarkers (21). Sedentary time was considered to be in-
terrupted if accelerometer counts rose up to or more than
100 counts per min (21). This can include behaviors that
result in a transition from sitting to a standing position or
from standing still to beginning to walk. Figure 2 is based
on data from two of our AusDiab accelerometer study par-
ticipants, showing a simple contrast between adults who have
the same total volume of sedentary time, but who break up
that time in contrasting patterns. The person whose data are
shown in the right-hand panel of Figure 2 (the ‘‘Breaker’’)
interrupts his or her sedentary time far more frequently than
the person whose data are shown on the left panel (the
‘‘Prolonger’’).
Independent of total sedentary time, moderate- to vigorous-
intensity activity time, and mean intensity of activity, we
found that having a higher number of breaks in sedentary
time was beneficially associated with waist circumference,
body mass index, triglycerides, and 2-h plasma glucose (21).
Figure 3 shows objectively measured waist circumference
across quartiles of breaks in sedentary time. Those in the
bottom quarter of the ‘‘breaks’’ distribution had, on average, a
6-cm larger waist circumference than did those in the top
quarter of that distribution (21).
These findings on breaks in sedentary time provide intrigu-
ing preliminary evidence on the likely metabolic health ben-
efits of regular interruptions to sitting time, which we would
argue are additional to the benefits that ought to accrue from
reducing overall sedentary time. Interestingly, in a recent study
(5), patterns of sedentary time accumulation (but not total
sedentary time) were shown to differ among four groups of
adults with various activity patterns (healthy group with active
occupation, healthy group with sedentary occupation, group
with chronic back pain, group with chronic fatigue syndrome).
As we will go on to propose, although we believe that these are
strongly indicative findings, there is the need to determine
whether these associations can be confirmed in experimental
manipulations of sitting time in the laboratory. Intervention
studies where sedentary time is reduced or broken up in natu-
ralistic settings such as the domestic environment or the
workplace would also be needed.
Sedentary Behavior and Mortality
The significance of the evidence on the adverse car-
diometabolic health consequences of prolonged sitting time
is underscored by findings from a mortality follow-up of par-
ticipants in the Canada Fitness Surveys. Canadians who
reported spending most of their day sitting had significantly
poorer long-term mortality outcomes than did those who
reported that they spent less time sitting. These relationships
with mortality were consistent across all levels of a self-report
Figure 2. Breaks in sedentary time: same amount of sedentary time,
but different ways of accumulation. CPM, counts per minute. (Reprinted
from Dunstan DW, Healy GM, Sugiyama T, Owen N. Too much sitting
and metabolic risk Vhas modern technology caught up with us? US
Endocrinol. 2009; 5(1):29Y33. Copyright *2009 Touch Briefings. Used
with permission.)
Figure 3. Associations of breaks in sedentary time with waist circum-
ference (based on data from Healy et al. (21)).
Volume 38 cNumber 3 cJuly 2010 Science of Sedentary Behavior 109
Copyright @ 2010 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
measure of overall sitting time. Participants estimated the
broad fractions of their waking hours that were spent sitting.
Importantly, the sitting timeYmortality relationships were
apparent even among those who were physically active and
the relationships were stronger among those who were over-
weight or obese (25). In a follow-up of AusDiab study parti-
cipants during 6.5 yr, high levels of TV time were significantly
associated with increased all-cause and cardiovascular disease
mortality rates (9). Each 1-h increment in TV time was found
to be associated with an 11% and an 18% increased risk of all-
cause and cardiovascular disease mortality rates, respectively.
Furthermore, relative to those watching less TV (G2hId
j1
),
there was a 46% increased risk of all-cause mortality and an
80% increased risk of cardiovascular disease mortality in those
watching TV 4 hId
j1
or more. These increased risks were
independent of traditional risk factors such as smoking, blood
pressure, cholesterol level, and diet, as well as leisure time
physical activity and waist circumference. A recent study from
the United States (47) examined sedentary behaviors in
relation to cardiovascular mortality outcomes based on 21 yr
of follow-up of 7744 men. Those who reported spending more
than 10 hIwk
j1
sitting in automobiles (compared with
G4hIwk
j1
) and more than 23 h of combined television
time and automobile time (compared with G11 hIwk
j1
)had
an 82% and 64% greater risk of dying from cardiovascular
disease, respectively. TV time alone was not a significant
predictor (47).
RESEARCH DIRECTIONS
Looking Back Through a Sedentary Behavior Lens
Emerging findings on sedentary behavior suggest a different
perspective through which findings of earlier physical activity
and health research studies may be reexamined (we thank
William L. Haskell, Ph.D., FACSM for stimulating these
observations). For example, physical activity epidemiology
studies that have assessed physical activity comprehensively
often have included measures of sitting time, which has been
used mainly to derive overall daily energy expenditure esti-
mates. We would predict (perhaps boldly) that if such studies
were to be revisited, with further analyses being conducted
using sitting time as a distinct exposure variable, that strong
evidence would be found for deleterious effects on subsequent
health outcomes, independent of those related to physical
inactivity.
Other potentially fruitful areas in which the relevance of
existing evidence could be reexamined are the NASA zero-
gravity studies. Comparing findings of those studies (which
relate to the metabolic consequences of extreme muscular
unloading) with those of the recent findings from inactivity
physiology (16,17) may yield further insights relating to the
underlying biology of prolonged sedentary time.
Research on physical activity and health had its roots
in early occupational epidemiological studies that assessed
workers in jobs that primarily involve sitting as the compar-
ison groups against which the protective benefits of physically
active work were highlighted (4,17,18). In the perspective of
the new evidence that we have highlighted, conducting fur-
ther occupational epidemiological studies using new objective
measurement capabilities and examining a range of cardio-
metabolic and inflammatory biomarkers as intermediate out-
comes could yield valuable insights.
Sedentary Behavior Research Strategy
Our population health research program on sedentary
behavior is guided by the behavioral epidemiology framework
(34,36). Figure 4 shows six research phases. As we previously
demonstrated, evidence within the first phase (examining
the relationships of sedentary behavior to cardiometabolic
biomarkers and health outcomes) has strengthened rapidly
during the past 10 yr.
Prolonged periods of sitting in people’s lives need to be
measured precisely (phase 2). Their contextual determinants V
that is, behavior settings (32,35) Vneed to be identified in
domestic, workplace, transportation, and recreation contexts
Figure 4. Behavioral epidemiology framework: phases of evidence for a population health science of sedentary behavior.
110 Exercise and Sport Sciences Reviews www.acsm-essr.org
Copyright @ 2010 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
(phase 3). We have argued previously for a research focus on
the distinct environmental determinants of sedentary behav-
iors, in contexts where they can be amenable to intervention
(31,32,37,41). The feasibility and efficacy of such inter-
ventions need to be tested rigorously (phase 4). Importantly,
public health policy responses need to be informed by evi-
dence from all of these phases. Compared with the challenges
for physical activity and public health (19), sedentary
behavior may be less of a ‘‘moving target’’ in this context and
may be shown to be a tractable public health objective (4).
The Population Health Science of Sedentary
Behavior: Research Opportunities
Different sedentary behaviors and their interactions with
physical activity need to be examined in a range of contexts.
For example, we have demonstrated that leisure time Internet
and computer use is related to overweight and obesity in
Australian adults (45), and that habitual active transport re-
duces the impact of TV time on body mass index (40). Having
identified these relationships, our program is now broadening
the evidence base through research with other populations.
New studies include work with the large population-based data
set from the NHANES from the United States, examining
potential racial and ethnic differences in the relationships of
total sedentary time and breaks in sedentary time with car-
diometabolic biomarkers. We have demonstrated significant
associations of TV time with excess body weight among high
school students in regional mainland China (52). In the con-
text of the rapid economic development and increasing urban-
ization among the populations of many developing countries,
documenting the health consequences of reductions in physi-
cal activity and increases in sedentary time will be crucial for
informing preventive health measures (38).
Studies with high-risk groups also are required. For exam-
ple, we examined accelerometer-derived physical activity,
sedentary time, and obesity in breast cancer survivors, show-
ing physical activity to be protective, but there was no dele-
terious relationship for sedentary time (28). Significant
prospective relationships of TV time with weight gain during
3 yr were identified in a large population-based cohort of
Australian colorectal cancer survivors (49). More such etio-
logic research is needed to examine potential relationships
between too much sitting and the development of other dis-
eases that have been linked to metabolic risk factors.
For the second phase of the behavioral epidemiology
framework (measurement; Fig. 4), there is the need to identify
the reliability and validity of self-report instruments (6).
Population-based descriptive epidemiological studies using
high-quality measures are needed. For example, we have
shown that Australian adults with lower levels of educational
attainment and those living in rural areas are more likely to be
in the highest TV time categories (7). We also have demon-
strated that for Australian women, being in the higher cate-
gories of TV time can be associated with a broader pattern of
leisure time sedentary behavior and with being less likely to
meet physical activity recommendations (39). Using Ameri-
can Cancer Society data from a large population-based study,
we have identified clusters of adults in the 4 h or more cat-
egory of TV time who are less educated, obese, and snacking
while watching TV (26).
Studies have begun to identify the environmental corre-
lates of sedentary behavior, and initial findings seem puzzling.
Among urban Australians, lower levels of objectively assessed
neighborhood walkability (poorly connected streets, low lev-
els of residential density, and limited access to destinations)
were found to be associated with higher TV time in women
(41). However, a recent study in the city of Ghent, Belgium,
showed higher levels of walkability to be associated with
higher amounts of accelerometer-assessed sedentary time (46).
These apparently contradictory outcomes require further
research. Such findings have potential implications for the
emerging area of research on built environment/obesity rela-
tionships, within which sedentary behavior is likely to have a
significant role (30).
Research on sedentary behaviors also needs to be extended
beyond the promising initial studies on TV time to under-
stand the potential health consequences of other common
sedentary behaviors. Evidence on the metabolic correlates of
prolonged sitting in motor vehicles would be particularly infor-
mative in the light of recent evidence on relationships with
premature mortality (47). The social and environmental
attributes associated with high levels of time spent sitting in
automobiles also need to be identified.
The highest priority for the sedentary behavior research
agenda is to gather new evidence from prospective studies,
human experimental work, and intervention trials. There is
the particular need to build on the promising findings on
relationships of sedentary time Voverall sitting time, TV
time, and time sitting in automobiles Vwith premature
mortality (9,25,47). Controlled experimental studies with
humans also should be particularly informative. For example,
we are currently conducting a laboratory study experimentally
manipulating different ‘‘sedentary break’’ conditions and ex-
amining associated changes in cardiometabolic biomarkers
(focusing on levels of triglycerides, glucose, and insulin).
Field studies also are needed on the feasibility and accept-
ability of reducing and breaking up occupational, transit, and
domestic sedentary time. For example, in a weight control
intervention trial for adults with type 2 diabetes, we are test-
ing the impact of a sedentary behavior reduction intervention
module and examining behavioral and biomarker changes
associated with reducing and breaking up sedentary time.
There are multiple research opportunities that can be
explored through integrating sedentary behavior change
intervention into physical activity trials. When accelerometer
data are gathered from such studies, sedentary time measures
can be derived (21,22,24), and unique hypotheses may readily
be tested. It is imperative that the field now moves to obtain
such evidence through intervention trials, which will take
the science beyond the inherent logical limitations of cross-
sectional evidence.
Eleven Research Questions for a Science of
Sedentary Behavior
1. Can further prospective studies examining incident
disease outcomes confirm the initial sedentary behavior/
mortality findings?
2. Can sedentary behavior/disease relationships be iden-
tified through reanalyses of established prospective
Volume 38 cNumber 3 cJuly 2010 Science of Sedentary Behavior 111
Copyright @ 2010 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
epidemiological data sets by treating sitting time as a
distinct exposure variable?
3. What are the most valid and reliable self-report and
objective measures of sitting time for epidemiological,
genetic, behavioral, and population health studies?
4. Are the TV time-biomarker relationships for women
pointing to important biological and/or behavioral sex
differences?
5. What amounts and intensities of activity might be
protective in the context of prolonged sitting time?
6. What genetic variations might underlie predispositions
to sit and greater susceptibility to the adverse metabolic
correlates?
7. What is the feasibility of reducing and/or breaking
up prolonged sitting time for different groups (older,
younger) in different settings (workplace, domestic,
transit)?
8. If intervention trials show significant changes in
sitting time, are there improvements in the relevant
biomarkers?
9. What are the environmental determinants of prolonged
sitting time in different contexts (neighborhood, work-
place, at home)?
10. What can be learned from the sitting time and seden-
tary time indices in built-environment/physical activity
studies?
11. Can evidence on behavioral, adiposity, and other bio-
marker changes be gathered from ‘‘natural experiments’’
(e.g., the introduction of height-adjustable workstations
or new community transportation infrastructure)?
PRACTICAL AND POLICY IMPLICATIONS OF
A SCIENCE OF SEDENTARY BEHAVIOR
Practical and policy approaches to addressing too much
sitting as a population health issue will involve innovations on
multiple levels. For example, public information campaigns
may emphasize reducing sitting time as well as increasing
physical activity. There may be more widespread use of in-
novative technologies that can provide more opportunities
to reduce sitting time (e.g., height-adjustable desks) or new
regulations in workplaces to reduce or break up extended
periods of job-related sitting. Active transport modes can be
promoted not only as opportunities for walking, but also as
alternatives to the prolonged periods that many people spend
sitting in automobiles. Providing nonsitting alternatives at
community entertainment venues or events also may be
considered. If evidence on the deleterious health impact of
too much sitting continues to accumulate as we predict, and if
such innovations are implemented, there will be the need for
systematic evaluations, particularly of approaches that have
the potential for broader dissemination.
Anecdotally, the recent experience in Australia has been
that initiatives in the final phase of the behavioral epidemi-
ology framework (‘‘using relevant evidence to inform public
health guidelines and policy’’) have already begun. This is
happening largely on the basis of the first-phase evidence
presented in Figure 4 (‘‘identifying relationships of seden-
tary behavior with health outcomes’’). For example, the
Australian National Preventative Health Task Force Report
includes explicit recommendations to address prolonged sit-
ting in the workplace in the context of reducing the burden
of overweight and obesity, type 2 diabetes, and cardiovas-
cular disease. The Western Australian state division of the
Heart Foundation included reducing sitting time in a 2009
statewide mass media campaign for obesity prevention. In the
state of Queensland, Health Promotion Queensland (a cross-
departmental body) commissioned an evidence-based review
in 2009 on health impacts and interventions to reduce
workplace sitting, with a view to future practical initiatives.
Thus, there are growing expectations in Australia that too
much sitting is a real and substantial risk to health. However,
it remains to be seen whether the science of sedentary
behavior will deliver consistent new findings in all of the
research areas that are needed to inform such innovations
(Fig. 4).
Given the consistency of research findings reported thus far
on sedentary behavior and health, we expect that in the near
future there will be a stronger body of confirmatory evidence
from prospective studies and intervention trials. Furthermore,
we predict that the next iteration of the Physical Activity and
Public Health recommendations of ACSM/AHA will include
a statement on the health benefits of reducing and breaking
up prolonged sitting time.
Acknowledgments
N. Owen is supported by a Queensland Health Core Research Infrastructure
grant and by a National Health and Medical Research Council (NHMRC)
Program grant funding (no. 301200; no. 569940). G.N. Healy is supported
by an NHMRC (no. 569861)/National Heart Foundation of Australia
(PH 08B 3905) Postdoctoral Fellowship. D.W. Dunstan is supported by a
Victorian Health Promotion Foundation Public Health Research Fellowship.
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