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Abstract

Despite the convincing evidence that physical activity reduces the risk of colon cancer, there are some aspects of the association that remain unclear. These include the appropriate timeframe of exposure, whether the intensity of physical activity matters, and whether sedentary behavior is a distinct risk factor. This review summarized the research that has investigated these issues. In terms of timing, physical activity at any age (with the exception of physical activity performed up to and including the late teens) has been shown to be associated with a significantly reduced risk of colon cancer. Physical activity performed between 30 and 50 years of age, as well as long-term or lifetime physical activity, has been most consistently shown to reduce risk. For intensity, research to date suggests that more intense activity (particularly vigorous activity) may be associated with a greater reduction in the risk of colon cancer for males but not for females. Finally, most of the studies that have investigated the effect of sedentary behavior on the risk of colon or colorectal cancer have shown an increased risk, suggesting that sedentary behavior may be a distinct risk factor for colon cancer.

Keywords

colon cancer colorectal cancer physical activity sedentary behavior

The association between physical activity and colorectal cancer is a well-researched topic; close to 100 studies have been published in this area, and countless articles, meta-analyses, and book chapters have reviewed this literature. The majority of research has found that the most active individuals have a lower risk of colon cancer than the least active, and the evidence from these studies has been judged to be convincing.¹ A recent meta-analysis found that the most active individuals reduce their risk of colon cancer by 24% (relative risk = 0.76, 95% confidence interval = 0.72, 0.81), with almost identical results found for males and females.² The strongest evidence for the biological mechanisms through which physical activity may lower colon cancer risk include decreasing the level of body fat and decreasing insulin resistance.³ Other proposed biological mechanisms include the effect of physical activity on vitamin D, insulin-like growth factors, adipokines, low-grade inflammation, immune function, oxidative stress, prostaglandins, and gastrointestinal transit time.³ The risk of rectal cancer is generally thought to not be associated with physical activity¹ and is thus not considered in this review.

The majority of research has found that the most active individuals have a lower risk of colon cancer than the least active.

Despite the extensive research and convincing evidence that physical activity reduces the risk of colon cancer, there are some aspects of the association that remain unclear.^2,4 Two of these issues include whether there are certain periods of life in which being active may lead to greater (or smaller) risk reductions and whether the intensity of physical activity matters. There is also emerging evidence that sedentary behavior, or too much sitting, may be a distinct risk factor for colon cancer that acts independently of physical activity.^5,6 The aim of this review is to summarize the research that has investigated these issues.

Methodology

Medline was used to search the literature for all publications in English on physical activity and colon or colorectal cancer published through September 2011. The following search strategy was used: (a) exercise or physical activity or walking or motor activity, (b) colon or colorectal or bowel, (c) cancer or neoplasm or carcinoma, and (d) and a combination of terms in a, b, and c.

Timing Review

Studies that investigated the association between colon or colorectal cancer and physical activity performed at 1 or more ages (eg, at 30 years), during 1 or more age periods (eg, between 30 and 39 years of age), and/or over a long term or the lifetime were included in the timing review. If more than 1 type of physical activity was presented in a single study (eg, occupational and recreational activity, or total, moderate and vigorous recreational activity) the result from the most “complete” physical activity variable reported was used.

Intensity Review

Papers that looked at the association between colon or colorectal cancer and physical activity of 2 or more types of intensity were included in the intensity review. If a study reported physical activity of 2 or more types of intensity at different ages and over the lifetime, the lifetime result was used in the intensity review.

Sedentary Behavior Review

Studies that looked at the association between colon or colorectal cancer and some kind of sedentary behavior, such as watching television, hours spent sitting per day, or years spent in sedentary work, were included in the sedentary review. Studies that assessed job-based sedentary behavior using activity levels based on job title and/or duties were included, although it has been argued that this method of assessment may reflect a lack of activity rather than prolonged sitting.⁶ Many of these studies, as well as those that assessed self-reported occupational activity, used sedentary work as the reference category to investigate the effect of standing and manual work on the risk of colon or colorectal cancer. In these instances the risk estimates and confidence intervals of the standing/light work versus sedentary/sitting work comparison were inverted and used in this review.

Data Extraction and Analysis

Risk estimates and associated 95% confidence intervals were extracted from each included study. If more than 1 level of exposure was presented, the highest versus lowest comparison was used in this review. Three studies reported 90% confidence intervals, which were converted to 95% confidence intervals.

Forest plots were made using the metan package in Stata 11.2 (StataCorp, College Station, TX). As measurement of the exposure and definition of the outcome varied greatly in the included studies no attempt was made to conduct a formal meta-analysis.

Timing of Physical Activity

Most of the studies that have investigated the association between physical activity and colon cancer have only measured physical activity performed at 1 point in time. In case–control studies this has often been the period 1 to 2 years prior to diagnosis (cases) or study participation (controls), whereas in cohort studies the referent period has often been the month or year before study participation.⁷ Relatively few studies have collected information about physical activity at several different points in time, and few have examined the association between long-term or lifelong physical activity and colon cancer risk. As such, the appropriate timeframe of exposure to physical activity is unclear.

Age-Specific Physical Activity

Eleven studies were identified that have examined the association between colon or colorectal cancer and physical activity performed at specific ages or during specific age periods.^4,8-17 Two of these studies found no association between colon cancer and age-specific physical activity but did not report any risk estimates,^13,17 and 1 study reported that physical activity performed in the past had approximately the same influence on colorectal cancer risk as physical activity performed recently, but again it did not report risk estimates.¹¹ This review will focus on the remaining 8 studies (Figure 1).^{4,8-10,12,14-16} Six of the 8 studies looked at recreational activity only,^{4,9,10,12,14,15} 1 study looked at combined recreational and occupational activity,¹⁶ and 1 study looked at commuting activity.⁸ All these studies adjusted for a range of potentially confounding variables. There is considerable overlap in the age periods used in these studies, so, to simplify, the midpoint of each age period was used to group the age periods by decade.

Figure 1.

Forest Plot of Studies That Have Investigated the Effect of Age-Specific Physical Activity on Colon or Colorectal Cancer Risk.

Late teens

Four studies have looked at physical activity performed in the late teens.^9,12,14-16 None of these studies found a dose–response relationship, and 3 of the 4 studies reported risk estimates between 0.95 and 1.05, suggesting that physical activity in this age period is not associated with the risk of colon/colorectal cancer (Figure 1). Although 1 case–control study found a nonsignificant risk reduction of 54%, this result was based on a very small number of cases (8) and the study did not provide any information about the validity or reliability of the tool used to measure physical activity.¹⁴

Age 20 to 29 years

Four studies have investigated the effect of physical activity performed between 20 and 29 years of age on colon cancer risk.^4,8,9,16 Three of these studies have found a greater than 40% risk reduction for the most active participants compared with the least active participants: one of these found a significant ~45% risk reduction for males and females,⁸ one found a significant 67% risk reduction risk of distal colon cancer among females but no association among males,⁴ and one found a nonsignificant 48% risk reduction for males and females combined.¹⁴ These 3 studies were all case–control studies however, which are more prone to problems such as recall and selection bias than cohort studies. In addition, only 1 of these 3 studies found a dose–response relationship,⁸ and only 1 study reported on the validity or reliability of their physical activity questionnaire.⁴ The only cohort study that has examined the association between physical activity performed in this age period and colon cancer risk found no association.⁹

Age 30 to 39 years

Six studies have investigated the effect of physical activity performed between 30 and 39 years of age on colon or colorectal cancer risk, 2 of which were cohort studies. One of these cohort studies, which used a physical activity questionnaire similar to other valid and reliable ones, found a significant 24% risk reduction and a dose–response relationship for males but no risk reduction for females.⁹ The other cohort study only included males and found no association between physical activity at age 30 years and the risk of colorectal cancer, although it did not report how physical activity at age 30 years was measured.¹⁰ The 4 case–control studies all found that physical activity performed between the ages 30 and 39 years significantly lowered the risk of colon/colorectal cancer in males and females, with risk reductions ranging from 30% to 69%,^8,12,15,16 and 3 of the 4 studies found a dose–response relationship.^8,12,16 While one of these 4 case–control studies was a large population-based study, the other 3 were hospital-based and recruited fewer than 500 cases. None of the case–control studies provided any information about the validity or reliability of their physical activity questionnaire.

Age 40 to 49 years

Three studies, all having a case–control design, have examined the association between physical activity performed between 40 and 49 years of age and the risk of colon cancer. Two of these studies found a 40% or greater risk reduction: one reasonably sized population-based study found a significant 40% to 46% reduction and dose–response relationship among both males and females,⁸ and one small hospital-based study found a significant ~59% risk reduction for males and females combined and a borderline nonsignificant dose–response relationship.¹⁶ Neither provided any information about questionnaire validity or reliability. One reasonably sized population-based study, using a questionnaire similar to others that have been found to be reliable, found no association between colon cancer and total recreational activity; however, it did find that vigorous activity performed in this age period was associated with a significant 45% reduced risk of distal colon cancer among males but not among females.⁴

Age 50+ years

The effect of physical activity performed after the age of 50 years on the risk of colon or colorectal cancer has been investigated in 5 case–control studies. Two found a significantly reduced risk (ranging from 46% to 79%) and a dose–response relationship for males and females combined,^12,16 although both were hospital-based studies with a relatively small number of participants, and neither reported the validity or reliability of the tool used to measure physical activity. Three larger studies, 1 hospital based and 2 population based, found no association.^4,8,16 One of the studies that reported no association for total recreational activity did find that vigorous activity performed after the age of 51 years was associated with a significantly reduced risk of distal colon cancer in both males and females.⁴

Lifetime or Long-Term Physical Activity

Twelve studies have investigated the effect of long-term or lifetime physical activity on colon or colorectal cancer risk (Figure 2).* Eight of these studies examined long-term or lifetime recreational activity,^{5,9,11,13,19-22} 2 studies have examined combined recreational and occupational activity,^16,18 1 study has examined occupational activity,²³ and 1 study looked at recreational, occupational, and commuting activity separately.⁸ All the studies adjusted for, or analyzed the effect of, a range of possible confounders.

Figure 2.

Forest Plot of Studies That Have Investigated the Effect of Lifetime or Long-Term Physical Activity on Colon or Colorectal Cancer Risk.

Five cohort studies have investigated this issue.^{9,13,19,21,22} Two have found that a high level of lifetime or long-term activity is associated with a significantly reduced risk of colon cancer (ranging from 18% to 25%),^9,13 whereas 1 study found a nonsignificant 50% risk reduction.¹⁹ Two of these studies reported using a valid and reliable questionnaire.^9,19 Neither of the remaining 2 cohort studies found an association.^21,22 One of these 2 studies used a valid and reliable questionnaire,²¹ but the other measured physical activity at different time points using different questionnaires with unknown validity or reliability.²²

All the 7 case–control studies that have investigated the effect of long-term or lifetime physical activity on colon or colorectal cancer risk have found a risk reduction,* with 5 finding a significant risk reduction (ranging from 26% to 63%) for males and/or females.^{8,11,16,18,20} Three of the 5 studies that reported a significant risk reduction also found a dose–response relationship.^8,11,16 One of the 2 studies that did not find a significant association between total lifetime physical activity and colon cancer found a significant dose–response relationship between lifetime vigorous activity and the risk of distal colon cancer among both males and females.⁴ Only 2 of the 7 case–control studies reported using a valid and/or reliable physical activity questionnaire.^4,20

Summary of Timing Review

Findings from studies that have investigated the effect of physical activity performed in specific age periods suggest that physical activity performed at any age, except prior to 20 years, is associated with a reduced risk of colon cancer. Physical activity performed between 30 and 50 years of age has been most consistently shown to reduce risk, although this conclusion is largely based on results from case–control studies that used physical activity questionnaires with unknown validity and reliability. Although it could be argued that 30 to 50 years is the age period in which physical activity may optimally reduce colon cancer risk, it is also possible that people are able to recall the amount of physical activity they performed in this age period more reliably than in other age periods.

Long-term or lifetime physical activity has also been consistently associated with a reduced risk of colon cancer, with the majority of cohort and case–control studies finding that performing a consistently high level of physical activity leads to a reduced risk. This makes sense from a biological perspective, as colon cancer develops over an extended period of time.²⁴

Intensity of Physical Activity

It has been suggested that physical activity of different aerobic intensities (ie, light, moderate, or vigorous activity) may have an impact on health in different ways^25,26 and, as such, should be treated as potentially independent influences on disease risk.²⁵ Activities can be generally classified as light, moderate, or vigorous according to their metabolic-equivalent (MET) value, with 1 MET equivalent to a resting metabolic rate obtained during quiet sitting.²⁷ On an absolute scale, activities with a MET value between 1.6 and 2.9 (such as standing and most household chores) are considered to be light intensity, activities with a MET value between 3.0 and 5.9 (such as walking for exercise, golf, and gardening) are considered to be moderate intensity, and activities with a MET value equal to or greater than 6.0 (such as running, swimming, and squash) are considered to be vigorous intensity.²⁶ More practically, light intensity activities are generally defined as those that do not cause a noticeable change in breathing rate; moderate activities are defined as aerobic activities in which a conversation can be maintained, or as activities that require moderate physical effort and cause a small increase in breathing and heart rate; and vigorous activities are defined as those in which it is difficult to maintain a conversation, or as activities that require hard physical effort and result in a large increase in breathing and heart rate.^28-30 The use of these terms is inconsistent however. Some studies have used the terms light, moderate, and/or vigorous to describe increasing durations (or “dose”) of physical activity rather than increasing intensity, and as discussed by others, a range of terms have been used to describe activity intensities.²⁸

The most recent Global, United States, United Kingdom, and Canadian physical activity guidelines have all placed a greater focus on vigorous intensity physical activity and have recommended it as an alternative or supplement to moderate intensity activity to meet the recommended weekly dose.^31-34 Recent literature reviews suggest that, compared with moderate intensity activity, vigorous intensity activity may lead to a greater reduction in the risk of cardiovascular disease³⁵ and all-cause mortality.³⁶ Epidemiologic studies of physical activity and colon cancer have generally compared the most active participants with the least active participants, and few have considered the effect of activities of different intensities. A previous review of the literature concerning physical activity and colon cancer suggested that it may be necessary to perform vigorous intensity physical activity to reduce risk⁷; however, it has also been proposed that a sufficient amount of walking may be all that is required to reduce the risk of colon cancer.^21,37

Ten studies (7 cohort and 3 case–control) were identified that have investigated the association between colon cancer and physical activity of 2 or more types of intensity.* Six reported results for males^4,9,20,40-42 (Figure 3), and all 10 studies reported results for females (Figure 4). Five studies asked participants to report the number of hours they spent in light to moderate or moderate intensity activity and in vigorous intensity activity,^{13,20,38,39,42} 3 studies asked about time spent walking or in light activity and in moderate-to-vigorous activity,^9,21,41 1 study asked about time spent walking and in vigorous activity,⁴⁰ and 1 study asked participants to list the activities they performed and then classified them as moderate or vigorous according to their MET value.⁴ All 10 studies adjusted for, or analyzed the effect of, a range of possible confounders. Eight studies analyzed the different intensity variables as independent risk factors,^† although only 5 of these studies report mutually adjusting the different physical activity intensity variables.^4,9,20,39,42

Figure 3.

Forest Plot of Studies That Have Investigated the Effect of Physical Activity of Different Intensities on Colon or Colorectal Cancer Risk Among Males.

Figure 4.

Forest Plot of Studies That Have Investigated the Effect of Physical Activity of Different Intensities on Colon or Colorectal Cancer Risk Among Females.

Two of the 3 cohort studies conducted in males looked at light and moderate-to-vigorous activity,^9,41 and 1 study looked at walking and vigorous activity⁴⁰ (Figure 3). All 3 studies found similar risk estimates for physical activity of different intensities.^9,40,41 All 3 studies reported that the physical activity questionnaire they used was valid and/or reliable. Conversely, all 3 of the population-based case–control studies conducted in males, 2 of which had a large sample size and used a valid and/or reliable questionnaire,^4,20 found a larger risk reduction for vigorous intensity activity than for light to moderate or moderate activity.^4,20,42

Five^9,38-41 of the seven^{9,13,21,38-41} cohort studies conducted in females found similar risk estimates for physical activity of different intensities in females (Figure 4). Two of these 5 studies looked at light and moderate-to-vigorous activity,^9,41 2 studies looked at moderate and vigorous activity,^38,39 and 1 study looked at walking and vigorous activity.⁴⁰ One cohort study found that moderate-to-vigorous activity was associated with a greater risk reduction than walking,²¹ whereas 1 study found a greater risk reduction for moderate activity than for vigorous activity.¹³ Most,^9,21,39-41 but not all,^13,38 of the cohort studies have reported that the questionnaire used to measure physical activity was valid and/or reliable. The 3 case–control studies that have investigated this issue in females have looked at light to moderate or moderate activity and vigorous activity.^4,20,42 One of these case–control studies found similar risk estimates for physical activity of different intensities,⁴² one found a greater risk reduction for vigorous activity,²⁰ and one found that vigorous activity was associated with a greater risk reduction for distal colon cancer but not proximal colon cancer.⁴ Two of the 3 case–control studies reported using a valid or reliable questionnaire.^4,20

Summary of Intensity Review

The research that has been conducted on physical activity and colon cancer risk suggests that more intense activity may lead to a greater risk reduction among males, but not for females. In particular, vigorous intensity activity appears to confer a greater risk reduction than moderate intensity activity among males, although this conclusion is based solely on results from 3 case–control studies, as no cohort studies have found that more intense activity has a greater effect. It is possible that several of the biological mechanisms through which physical activity may reduce colon cancer risk, such as decreased obesity, greater insulin sensitivity, and decreased levels of insulin-like growth factors, may be associated with vigorous activity rather than moderate activity.⁷ Another possible explanation is that vigorous intensity physical activity is recalled more reliably than moderate intensity,^43,44 meaning that vigorous activity is better able to distinguish between highly active and inactive participants.²⁰

Sedentary Behavior

Sedentary behavior refers to prolonged sitting and other activities that require very low energy expenditure, such as watching television or working at a desk. There is an emerging body of evidence suggesting that sedentary behavior is an independent risk factor for several chronic diseases, distinct from insufficient physical activity.⁴⁵ Importantly, many of these studies indicate that sedentary behavior has negative health effects even among people who meet physical activity guidelines.⁴⁵

A recent review of the literature concerning sedentary behavior and cancer concluded that sedentary behavior may be associated with an increased risk of colorectal, prostate, ovarian, and endometrial cancers.⁶ A low level of occupational activity has been shown to be associated with an increased risk of colon cancer⁴⁶; however, many of the studies in this area have combined sedentary and light activities and/or have compared the most active participants with the least active participants. As such, it not clear whether a high level of activity, a high level of sedentary behavior (sitting), or a combination of both is behind the associations found in those studies.⁵ As has been discussed by others, many studies have used the term sedentary as a synonym for no or low physical activity but have not actually measured sedentary behavior (ie, prolonged sitting).^6,25

A total of 16 studies (6 cohort and 10 case–control) were identified that have investigated the effect of some form of sedentary behavior on colon or colorectal cancer risk (Figure 5).^{5,9,12,17,47-58} The majority have examined sedentary behavior in an occupational setting.^† Two studies have examined time spent watching television,^9,55 and 2 studies have examined total hours sitting per day.^9,58

Figure 5.

Forest Plot of Studies That Have Investigated the Effect of Sedentary Behavior on Colon or Colorectal Cancer Risk.

Fourteen of the 16 studies have found that sedentary behavior increases the risk of colon or colorectal cancer,^† although only 5 studies report a statistically significant increased risk (Figure 5).^5,9,17,51,55 Six cohort studies have investigated this issue, with 2 finding a statistically significant increased risk (ranging from 30% to 56%),^9,51 2 finding a nonsignificant increased risk (ranging from 22% to 76%),^48,56 and 2 finding no effect.^50,52 All except one of the cohort studies assessed sedentary behavior using self-report. Ten case–control studies have investigated the effect of sedentary behavior on colon or colorectal cancer risk. Three have found a statistically significant increased risk, ranging from 54% to 94%,^5,17,55 and the other 7 have reported nonsignificant increased risks, ranging from 18% to 67%.^‡ Six of the case–control studies have been hospital-based studies, and 6 have relied on job titles to assess sedentary behavior. None of the cohort or case–control studies measured sedentary behavior using a tool that has been shown to be valid or reliable for assessing sitting time. Although all the included studies adjusted for at least age in their analyses, only 6 adjusted for recreational physical activity. Two of these found that sedentary behavior significantly increased risk,^5,9 2 found a nonsignificant increased risk,^53,54 and 2 found no association.^50,52 One study found that recreational physical activity did not modify the effect of sedentary work (ie, long-term sedentary work was associated with an increased risk even among the most recreationally active participants).⁵

Summary of Sedentary Behavior Review

The majority of studies that have investigated the effect of some kind of sedentary behavior (sitting) on colon cancer have shown an increased risk. However, much of this evidence comes from studies that have based occupational activity on job title, a method that may mistakenly classify jobs requiring a low level of activity but not prolonged sitting as sedentary.⁶ In addition, many of the studies that have investigated this issue have been hospital-based case–control studies, which are more prone to problems such as selection bias and recall bias and/or have been small studies with insufficient power to detect a statistically significant difference. Furthermore, few studies have assessed the potential confounding effect of aerobic physical activity, although 4 of the 6 studies that have adjusted for physical activity found that sedentary behavior was associated with an increased risk of colon cancer.

Despite these methodological problems, the research conducted in this area so far indicates that sedentary behavior may be a risk factor for colon cancer, independently of physical activity. Another way to consider this may be that light intensity activity, which has previously thought to have no impact on disease risk, may actually lead to health benefits (such as a reduced risk of colon cancer) when it is replacing sedentary behavior.²⁶ The effect of too much sitting on adiposity, metabolic dysfunction, inflammation, and vitamin D have been proposed to be the pathways through which sedentary behavior may influence colon cancer risk.^5,6

Conclusion

Despite the convincing evidence that physical activity reduces the risk of colon cancer, there are some aspects of the association that remain unclear, such as the appropriate timeframe of exposure, whether the intensity of physical activity matters, and whether sedentary behavior is a distinct risk factor for colon cancer. The aim of this review was to summarize the research that has investigated these issues.

Research that has investigated the effect of physical activity performed in specific age periods on colon cancer suggests that activity at any age is associated with a significantly reduced risk, with the exception of physical activity performed up to and including the late teens. Physical activity performed between the ages of 30 and 50 years, as well as long-term or lifetime physical activity, has been most consistently shown to reduce risk. Research to date suggests that more intense activity may be associated with a greater reduction in the risk of colon cancer for males, but not for females, whereas most of the studies that have investigated the effect of some type of sedentary behavior on the risk of colon or colorectal cancer have shown an increased risk. From a public health perspective, these conclusions suggest that programs that encourage people to establish and/or maintain a high level of physical activity consistently throughout their lifetime should be supported. In addition, people already engaging in moderate intensity activity could be encouraged to also perform some vigorous intensity physical activity, if physically capable. Finally, programs that discourage long bouts of sitting, in both occupational and nonoccupational settings, should be introduced.

Future Research Directions

Where possible, future research on physical activity and colon cancer should collect information on sedentary behavior and light, moderate, and vigorous intensity activity (based on established definitions of these terms) using valid and reliable instruments; clearly report the definitions of the intensity terms; and investigate whether they have independent influences on the risk of colon cancer. Future research could also investigate whether nonaerobic activity, such as resistance training, is associated with colon cancer risk and, if so, whether this is independent of aerobic activity. In addition, future studies should investigate whether obesity, diet, and/or ethnicity modify the effect of physical activity on colon cancer and whether physical activity has a different effect on proximal and distal colon cancers.²

Footnotes

Acknowledgements

Terry Boyle is supported by PhD scholarships from The University of Western Australia and the Lions Cancer Institute of Western Australia. The contributions of Professors Lin Fritschi, Jane Heyworth, and Fiona Bull are gratefully acknowledged.

*

References 4, 8, 9, 11, 13, 16, 18-23.

†

References 4, 8, 11, 16, 18, 20, 23.

*

References 4, 9, 13, 20, 21, 38-42.

†

References 4, 9, 13, 20, 21, 39, 40, 42.

†

References 5, 12, 17, 47-54, 56, 57.

†

References 5, 9, 12, 17, 47-49, 51, 53-58.

‡

References 12, 47, 49, 53, 54, 57, 58.

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Physical Activity and Colon Cancer

Abstract

Keywords

Methodology

Timing Review

Intensity Review

Sedentary Behavior Review

Data Extraction and Analysis

Timing of Physical Activity

Age-Specific Physical Activity

Late teens

Age 20 to 29 years

Age 30 to 39 years

Age 40 to 49 years

Age 50+ years

Lifetime or Long-Term Physical Activity

Summary of Timing Review

Intensity of Physical Activity

Summary of Intensity Review

Sedentary Behavior

Summary of Sedentary Behavior Review

Conclusion

Future Research Directions

Footnotes

Acknowledgements

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References