Res Exerc Epidemiol 2011; 13(1): 30-35.
c 2011 by the Japanese Association of Exercise Epidemiology
Copyright ○【Review Article】

When Meeting Physical Activity Guidelines is not Enough:the Interplay of Sedentary and Active Behaviors
Geoffrey Whitfield1)

Kelley K. Pettee Gabriel1)

Harold W. Kohl III1,2)

1）Division of Epidemiology, Human Genetics, and Environmental Sciences, Universityof Texas School of Public Health, Texas, USA2）Department of Kinesiology and Health Education, The University of Texas, Texas, USA

ABSTRACT The combined effects of physical activity (PA) and sitting time on health have been inadequately
studied. Sitting time has not been thoroughly measured in existing studies. The high prevalence of sitting inmodern society may well present a situation where merely meeting guidelines is insufficient to realize healthbenefits. Identifying a dose of PA that negates the harmful effects of prolonged sitting should be a priority as
research into the health effects of sitting progresses. Utilizing a group of high socio-economic status, highly active
subjects of varying PA volume may allow identification of such a threshold, which may, in turn, shed light on
more effective PA recommendations for highly sedentary individuals. Additional investigations into different
sitting contexts, enhanced measurement techniques, and expanded surveillance may also be warranted.
Key words: sedentary behavior, sitting time, physical activity guidelines

Introduction

heart disease, certain cancers, and diabetes. By
compliment, lack of physical activity increases ones
risk for these diseases.
Currently, little doubt remains over the positive
health effects of regular PA. The effect of PA on
cardiovascular disease risk is particularly strong.
Longitudinal studies in men and women have shown
reductions in cardiovascular and all-cause mortality
across categories of increasing volume of PA andphysical fitness, which is a physiological consequenceof PA4-7). The consistency of these findings, and manyothers, prompted the US Department of Health andHuman Services to establish PA guidelines, publishedin 20088). These Guidelines join a growing collection
from around the world (WHO, Canada, UK, Japan).
Despite this clear benefit, a recent analysis by Troiano
et al of accelerometer data from the National Healthand Nutrition Examination Survey showed that theprevalence of meeting PA guidelines may be as low as
5% of the US population9). This is countered bysurveillance data that suggest nearly 70% of US adults
can be classified as “meeting guidelines” 10). Worldwide, PA prevalence data are varied but World HealthOrganization estimates categorize 60% of the world’s

In recent decades, physical activity (PA) has beenshown to protect against several chronic diseases
including cardiovascular disease, diabetes, andcancers of the breast and colon1). The severity andpublic health impact of these conditions are clear:cardiovascular disease alone caused over 800,000
deaths in the United States (U.S.) in 20072). In
response to the vast public health burden attributable
to chronic disease, the U.S. Association of Schools of
Public Health released a document detailing publichealth priorities for the Obama administration 3).
Included in this document were five chronic diseases
that are responsible for over 66% of annual deaths in
the U.S.: heart disease, stroke, cancer, chronic obstructive pulmonary disease, and diabetes. Substantial
evidence supports the protective role of PA against
Address for correspondence: Geoffrey Whitfield; Divisionof Epidemiology, Human Genetics, and Environmental
Sciences, University of Texas School of Public Health;1616 Guadalupe Street, suite 6.300, Austin, TX 78701,
USA; Geoffrey.P.Whitfield@uth.tmc.edu

30Res Exerc Epidemiol 2011; 13(1): 30-35.

population as insufficiently active 11).
Though PA is beneficial for health, technologicalprogress has engineered PA out of various facets ofdaily life, replacing previously active behaviors withsedentary alternatives. Major examples can be seenin transportation and industry: since the Industrial
Revolution, the automobile has replaced walking as aform of locomotion for many people while mechanization and robotics have reduced previously laborintensive manufacturing jobs to manipulation of handcontrols. The trend continues in the home with themechanization of dishwashing and laundry. Even thesmallest of movements are being eliminated, evidenced by power windows in automobiles that not
only eliminate the hand-crank, but also eliminate theburden of fully depressing the “down” switch. The
success and innovation of the human species havequietly reduced energy expenditure throughout the day.
This has effectively reduced the minimum energy
expenditure necessary to survive for our species. The
continuing decrease in physical activity would seem torequire a closer inspection of increased sedentary timeand health.
Recently, the classification of sedentary behavior
has been refined. It is no longer acceptable to view
sedentariness as the absence of PA12). It is quitepossible to attain or exceed recommended levels of PA
with a daily, thirty-minute exercise session while

Figure 1.

spending the rest of the day seated at or near 1.5
metabolic equivalents (METS). This supposition isstrengthened by data from the 2009 American Time
Use Survey (ATUS) that reveals less than 6% ofleisure time is spent in “exercise, sports, andrecreation”13). Under this all-to-likely scenario, up to
15.5 of 16 waking hours (97%) could be spent riding
in cars, trains, elevators, and sitting at desks or on the
couch. Researchers have coined the term “active
couch potato” to describe this juxtaposition of active
individuals that concomitantly display long durationsof sedentary behavior12)(Fig.1). Additionally, sedentary behaviors have been further subdivided intolevels of sedentariness, much the way PA is subdivided into intensities. For example, quiet standing
requires contraction of postural muscles to counter
gravity and provide stability. Sitting, on the other hand,allows many large support muscles in the legs andtorso to remain unloaded for long periods: the surface
upon which one sits bears ones weight and provides ameasure of stability. As a consequence, recent
research in this area has focused on sitting as an
exposure that is distinct from inactivity12,14-17). The
purpose of this paper is to review findings on theinterplay of sitting behaviors and physical activity anddiscuss new avenues of research that may help
advance this topic.

Hypothetical distribution of daily minutes in sufficiently active individuals with differing volumes
of work-time sitting.
31Res Exerc Epidemiol 2011; 13(1): 30-35.

Research on sitting

those attaining recommended levels of PA, sitting time,assessed as TV viewing time, may pose a health risk.
The AUSDIAB results are not alone. In 2003, Hu etal published an analysis of prospective data from the
Nurses’ Health Study16). They were able to show asignificant trend for increasing obesity and Type II
diabetes risk across categories of increasing TV
viewing time. Again, this trend remained significant
after adjusting for covariates including a measure of
exercise participation.
As noted above, there exists a rationale for utilizing
TV time as a proxy for total sitting, but the measure isfar from perfect. First, it is unlikely that TV viewing
time fully captures the extent of daily sitting. For
example, an individual may spend 8-10 hours per day
standing and walking during classroom teaching,while another spends 8-10 hours per day sitting whilewriting computer programs (as in figure 1). They may
validly report equal TV viewing time while experiencing dramatically different exposures to total sitting
time. TV time may also be accompanied by exercise:gyms frequently have banks of TVs in front ofcardiovascular equipment to better entertain theirclientele. Finally, TV time may be confounded bynutritional intake. Those watching more TV may be
more exposed to food advertising which may, in turn,drive increased caloric consumption. Despite thelimitations, TV time has contributed to our understanding of the sitting-health relationship, but improved measures are needed, as discussed below.

Clinical research into the effects of muscle
unloading began several decades ago, with the aim ofunderstanding the effects of prolonged weightlessness,simulated by forced bed-rest or prolonged water
immersion18,19). In animal models and human studies,changes to metabolic processes, including lipoprotein
lipase dysfunction and insulin resistance, can begin
only four hours after unloading occurs20,21), providing
a physiological precedent to acute effects of prolonged
sitting.
In contrast to well-controlled clinical experiments,
population studies on free-living sitting behaviors are
relatively new. In these studies, it is presumed thatvariables used to assess sitting time are behavioral
markers for the amount of time a person spends during
her or his waking hours at or near resting metabolism.
Moreover, a consistent definition of sitting behaviors
has been elusive.
A prominent example of early research in this areais the AUSDIAB study that began in 1999 withfollow-up studies in 2004 and 200922). In this large
sample, sitting time was assessed by proxy as selfreported daily television (TV) viewing time. This isused because the vast majority of TV viewing occurs
while seated and the division of programming into
regular blocks of time which facilitates more accurate
recall via self-report measures.
Results from the AUSDIAB studies have produced
a wealth of information and an emerging trend. In
2004, Dunstan et al showed that, compared to thosewith the least TV viewing time, men and women withthe most TV time were more likely to have undiagnosed diabetes. Additionally, women with themost TV time were more likely to have impaired
glucose tolerance than those with the least TV time.
Interestingly, these results remained significant after
adjustment for covariates, including total PA time 17).
In a follow-up study in 2005, Dunstan et al showedthat women watching TV for more than 14 hours per
week were more likely to have the metabolic
syndrome than those watching for seven hours or
fewer. This relationship was only slightly attenuatedwhen adjusted for other factors, including time spent
in PA14). These results indicated that even among

Sitting among the physically active
The previous studies hinted that excessive sitting
may at best attenuate, or at worst overwhelm, thepositive health effects of regular PA. To better
examine the interrelationships among sitting behaveiors, PA, and cardiometabolic health, the AUSDIAB
group analyzed a subset of their study population thatmet PA guidelines. Using multivariate linear regression across quartiles of increasing TV time, they
showed significant trends for increasing waist
circumference, systolic blood pressure, and two-hour
plasma glucose in men, while women also showedsignificant trends for increasing fasting plasma
glucose, triglycerides, and decreasing HDL choles-

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Res Exerc Epidemiol 2011; 13(1): 30-35.

terol15). Thus, the “active” group met physical activity
guidelines for health, yet the sitting time in which they
participated had significant deleterious associations
with markers of cardiometabolic health. Taken
together, these studies suggest that the ill effects ofprolonged sitting remain after accounting for the
positive effects of PA.
In summarizing this literature, an importantquestion emerges: is there a dose of PA volume that
protects against the effects of prolonged sitting 12) ?
Evidence that such a threshold may exist is provided
by Katzmarzyk, et al. In this prospective study ofphysical activity, sitting time and mortality, asignificant dose-response relationship was observed
between sitting time and both all-cause andcardiovascular disease mortality in a sample ofCanadian adults. Stratification by physical activity
revealed an attenuated, but still significant doseresponse relationship among those with an energy
expenditure equivalent to meeting PA guidelines23).
Though the outcome in this study differs from thoseprevious, it reinforces the question: if some PA
attenuates a particular negative effect of sedentarytime, will more PA eliminate it?
One avenue of research that may help answer thisimportant question is the effect of prolonged sitting inhighly active individuals: those who do not simply
meet PA guidelines, but far exceed them. In practice,
this line of research would study the upper tail of the
PA distribution normally seen in population-based
studies. Although limited in generalizability, seeking
this population out and studying them directly would
provide the sample sizes across several strata of
high-volume PA needed to investigate the existence ofa protective threshold of PA. In essence, if such athreshold is not seen in this population, it is not likely
to be seen.
Currently, endurance sports such as running,
triathlon, and cycling are enjoying a surge in
popularity. According to runningusa.org, participationin marathons in the US increased 10% from 2008 to
2009, the largest-ever single-year increase. The
duration and intensity of training required for these
events creates a population that far exceeds therecommendation for 75 or 150 minutes per week ofvigorous- or moderate-intensity PA, respectively. The

variety of distances offered, from sprint triathlons(roughly 400 m swimming, 20 km bicycling and 5 km
running) and 5-kilometer runs to century (100-mile)
bicycle rides, marathons, and iron-distance triathlon(3.6 km swimming, 180 km bicycling, 42 km running)likely creates meaningful strata of PA within thishighly active population. Additionally, participation inthese events tends to cater towards educated, uppermiddle class individuals that may be more likely tohold seated occupations: the 2010 Austin Marathon(Austin, Texas, USA) reported a field that was 70%
college-educated with a median annual income over
$75,00024). These events create a base population fromwhich to draw the active sample described previously.
While many would argue against the generalizabilityof findings from such a sample, the opportunity for
information on a dose of PA that protects against
sedentary-related chronic disease should outweigh thiscriticism.
If such a dose of PA volume is identified, it may
drive important policy and public health recommendations. For example, labor regulations may recognize
the hazardous conditions experienced by seatedworkers and mandate appropriate interventions.
Additionally, those in traditionally seated occupations
such as computer programming or data entry may
warrant a different PA guideline than those in occupations usually associated with standing and lightactivity such as classroom teaching or retail work. In
this manner, it may provide a definitive recommendation that can replace the adage “some exercise isgood, but more is better.”

Future directions
In addition to identifying a dose of PA that protects
against the harmful effects of prolonged sitting,several other key areas of interest in this area deserve
continued attention. One such question is whether
different domains of sitting have differing healtheffects. One criticism of using TV time as a measureof global sitting is that the relationship between TV
time and health outcomes may be confounded byexposure to food advertising and thus excessive
snacking12). Hu et al showed differences in risk ofobesity between sitting at work and sitting while

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Res Exerc Epidemiol 2011; 13(1): 30-35.

watching television16). It is quite possible that otherseated activities, including driving and the accompanying stress, may have differing effects. Individual
instruments or combinations of measures that accurately assess sitting across different contexts areneeded, and should allow more precise analyses of therelation between sitting and health outcomes.
In addition to improved self-report measures ofsitting behaviors, direct measures of body position,such as the ActivPaltm 25), may provide an important
advancement in assessing sitting and related sedentary
behaviors. As noted above, standing requires additional muscular contractions for postural stability andmay provide a distinct physiological stimulus, thereby
necessitating a distinction in measurement. Many
activity monitors, including those used in NHANES
2003-06 (ActiGraph Model 7164; Pensacola, FL),
cannot differentiate between quiet sitting and motionless standing. When stationary, both behaviors
will be recorded as zero intensity counts. Recently,
newer ActiGraph models such as the GT3X include an
inclinometer, which can be used to detect positionalchange. Unfortunately, evidence for the reliability andvalidity of this feature in free-living situations is still
emerging.
Public health significance is a function of prevalence and severity. A rare but highly fatal disease willdraw attention, as will a minor, but widely spreadcondition. As noted previously, sedentary behaviors ingeneral, and sitting in particular, have increased withindustrial and technological modernization. In a recent
analysis of nationally-representative US accelerometer
data, Tudor-Locke et al found that greater than 50% of
waking hours were spent in sedentary pursuits while
only 20% of hours were spent in light, moderate, orvigorous intensity PA26). With such a large prevalence,even if the risk associated with prolonged sitting isminor, it may pose a significant public health hazard.
This argues for enhanced surveillance of sitting andother sedentary behaviors in countries around theglobe.

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