Active Transportation and Cardiovascular Disease Risk Factors in U.S. Adults

  • Gregg L. Furie
    Affiliations
    Robert Wood Johnson Foundation Clinical Scholars Program, Yale School of Medicine, New Haven, Connecticut

    VA Connecticut Healthcare System, Department of Veterans Affairs, West Haven, Connecticut
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  • Mayur M. Desai
    Correspondence
    Address correspondence to: Mayur M. Desai, PhD, MPH, Yale School of Public Health, 60 College Street, Room 402, New Haven, CT 06520
    Affiliations
    Robert Wood Johnson Foundation Clinical Scholars Program, Yale School of Medicine, New Haven, Connecticut

    Department of Chronic Disease Epidemiology, Yale School of Public Health, New Haven, Connecticut
    Search for articles by this author

      Background

      Evidence of associations between active transportation (walking and bicycling for transportation) and health outcomes is limited. Better understanding of this relationship would inform efforts to increase physical activity by promoting active transportation.

      Purpose

      This study examined associations between active transportation and cardiovascular disease risk factors in U.S. adults.

      Methods

      Using the 2007–2008 and 2009–2010 cycles of the National Health and Nutrition Examination Survey (NHANES), adults (N=9933) were classified by level of active transportation. Multivariable linear and logistic regression analyses controlled for sociodemographic characteristics, smoking status, and minutes/week of non-active transportation physical activity. Analyses were conducted in 2011.

      Results

      Overall, 76% reported no active transportation. Compared with no active transportation, mean BMI was lower among individuals with low (−0.9, 95% CI= −1.4, −0.5) and high (−1.2, 95% CI= −1.7, −0.8) levels of active transportation. Mean waist circumference was lower in the low (−2.2 cm, 95% CI= −3.2, −1.2) and high (−3.1 cm, 95% CI= −4.3, −1.9) active transportation groups. The odds of hypertension were 24% lower (AOR=0.76, 95% CI=0.61, 0.94) and 31% lower (AOR=0.69, 95% CI=0.58, 0.83) among individuals with low and high levels of active transportation, respectively, compared with no active transportation. High active transportation was associated with 31% lower odds of diabetes (AOR=0.69, 95% CI=0.54, 0.88). Active transportation was not associated with high-density lipoprotein level.

      Conclusions

      Active transportation was associated with more-favorable cardiovascular risk factor profiles, providing additional justification for infrastructure and policies that permit and encourage active transportation.

      Introduction

      Nearly 40% of adults in the U.S. do not obtain the minimum 150 minutes/week of moderate physical activity recommended by the DHHS,
      • Tucker J.M.
      • Welk G.J.
      • Beyler N.K.
      Physical activity in U.S. adults: compliance with the Physical Activity Guidelines for Americans.
      CDC
      Prevalence of self-reported physically active adults—U.S., 2007.
      increasing their chances of acquiring cardiovascular disease risk factors such as obesity,
      • Hankinson A.L.
      • Daviglus M.L.
      • Bouchard C.
      • et al.
      Maintaining a high physical activity level over 20 years and weight gain.
      • Slentz C.A.
      • Duscha B.D.
      • Johnson J.L.
      • et al.
      Effects of the amount of exercise on body weight, body composition, and measures of central obesity: STRRIDE—a randomized controlled study.
      hypertension,
      • Whelton S.P.
      • Chin A.
      • Xin X.
      • He J.
      Effect of aerobic exercise on blood pressure: a meta-analysis of randomized, controlled trials.
      diabetes,
      • Knowler W.C.
      • Barrett-Connor E.
      • Fowler S.E.
      • et al.
      Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin.
      • Hu G.
      • Lindstrom J.
      • Valle T.T.
      • et al.
      Physical activity, body mass index, and risk of type 2 diabetes in patients with normal or impaired glucose regulation.
      and serum lipid abnormalities.
      • Kodama S.
      • Tanaka S.
      • Saito K.
      • et al.
      Effect of aerobic exercise training on serum levels of high-density lipoprotein cholesterol: a meta-analysis.
      Despite evidence of physical activity's health benefits, particularly for sedentary populations,
      • Blair S.N.
      • Kampert J.B.
      • Kohl 3rd, H.W.
      • et al.
      Influences of cardiorespiratory fitness and other precursors on cardiovascular disease and all-cause mortality in men and women.
      efforts to increase population levels of leisure-time or occupational physical activity have not achieved desired results. Active transportation (walking and bicycling for transportation) may provide an alternative opportunity for physical activity. By transforming routine daily living into an opportunity for physical activity, active transportation overcomes many of the traditional barriers to engaging in leisure-time or occupational physical activity.
      • Hamer M.
      • Chida Y.
      Active commuting and cardiovascular risk: a meta-analytic review.
      Public policy and built environment interventions could increase levels of active transportation,
      • de Nazelle A.
      • Nieuwenhuijsen M.J.
      • Antó J.M.
      • et al.
      Improving health through policies that promote active travel: a review of evidence to support integrated health impact assessment.
      • Buehler R.
      • Pucher J.
      • Merom D.
      • Bauman A.
      Active travel in Germany and the U.S.: contributions of daily walking and cycling to physical activity.
      but justifying these efforts on the grounds of health promotion requires stronger evidence that active transportation, like other forms of physical activity, is associated with clinically meaningful health outcomes.
      Numerous observational studies have demonstrated a protective effect of leisure-time physical activity on cardiovascular disease risk factors. However, studies
      • Hamer M.
      • Chida Y.
      Active commuting and cardiovascular risk: a meta-analytic review.
      • Wanner M.
      • Gotshci T.
      • Martin-Diener E.
      • Kahlmeier S.
      • Martin B.W.
      Active transport, physical activity, and body weight in adults: a systematic review.
      of active transportation have shown inconsistent effects. Further, studies conducted in Scandinavia,
      • Andersen L.B.
      • Schnohr P.
      • Schroll M.
      • Hein H.O.
      All-cause mortality associated with physical activity during leisure time, work, sports, and cycling to work.
      • Hu G.
      • Qiao Q.
      • Silventoinen K.
      • et al.
      Occupational, commuting, and leisure-time physical activity in relation to risk for type 2 diabetes in middle-aged Finnish men and women.
      • Hu G.
      • Eriksson J.
      • Barengo N.C.
      • et al.
      Occupational, commuting, and leisure-time physical activity in relation to total and cardiovascular mortality among Finnish subjects with type 2 diabetes.
      • Barengo N.C.
      • Hu G.
      • Lakka T.A.
      • et al.
      Low physical activity as a predictor for total and cardiovascular disease mortality in middle-aged men and women in Finland.
      • Barengo N.C.
      • Hu G.
      • Kastarinen M.
      • et al.
      Low physical activity as a predictor for antihypertensive drug treatment in 25-64-year-old populations in eastern and south-western Finland.
      • Hu G.
      • Sarti C.
      • Jousilahti P.
      • et al.
      Leisure time, occupational, and commuting physical activity and the risk of stroke.
      • Wennberg P.
      • Lindahl B.
      • Hallmans G.
      • et al.
      The effects of commuting activity and occupational and leisure time physical activity on risk of myocardial infarction.
      • Hu G.
      • Tuomilehto J.
      • Borodulin K.
      • Jousilahti P.
      The joint associations of occupational, commuting, and leisure-time physical activity, and the Framingham risk score on the 10-year risk of coronary heart disease.
      • Hu G.
      • Jousilahti P.
      • Borodulin K.
      • et al.
      Occupational, commuting and leisure-time physical activity in relation to coronary heart disease among middle-aged Finnish men and women.
      • Hu G.
      • Jousilahti P.
      • Antikainen R.
      • Tuomilehto J.
      Occupational, commuting, and leisure-time physical activity in relation to cardiovascular mortality among Finnish subjects with hypertension.
      • Wang Y.
      • Tuomilehto J.
      • Jousilahti P.
      • et al.
      Occupational, commuting, and leisure-time physical activity in relation to heart failure among Finnish men and women.
      Australia,
      • Ming Wen L.
      • Rissel C.
      Inverse associations between cycling to work, public transport, and overweight and obesity: findings from a population based study in Australia.
      and Asia
      • Hayashi T.
      • Tsumura K.
      • Suematsu C.
      • et al.
      Walking to work and the risk for hypertension in men: the Osaka Health Survey.
      • Hu G.
      • Pekkarinen H.
      • Hänninen O.
      • Tian H.
      • Guo Z.
      Relation between commuting, leisure time physical activity and serum lipids in a Chinese urban population.
      • Hu G.
      • Pekkarinen H.
      • Hänninen O.
      • et al.
      Commuting, leisure-time physical activity, and cardiovascular risk factors in China.
      may lack generalizability to U.S. adults because of different racial and ethnic composition, transportation policies and infrastructure, and cardiovascular disease risk profiles. Two U.S. studies focused only on adults aged 18–28 years
      • Gordon-Larsen P.
      • Nelson M.C.
      • Beam K.
      Associations among active transportation, physical activity, and weight status in young adults.
      and aged 38–50 years.
      • Gordon-Larsen P.
      • Boone-Heinonen J.
      • Sidney S.
      • et al.
      Active commuting and cardiovascular disease risk: the CARDIA study.
      Importantly, these studies
      • Andersen L.B.
      • Schnohr P.
      • Schroll M.
      • Hein H.O.
      All-cause mortality associated with physical activity during leisure time, work, sports, and cycling to work.
      • Hu G.
      • Qiao Q.
      • Silventoinen K.
      • et al.
      Occupational, commuting, and leisure-time physical activity in relation to risk for type 2 diabetes in middle-aged Finnish men and women.
      • Hu G.
      • Eriksson J.
      • Barengo N.C.
      • et al.
      Occupational, commuting, and leisure-time physical activity in relation to total and cardiovascular mortality among Finnish subjects with type 2 diabetes.
      • Barengo N.C.
      • Hu G.
      • Lakka T.A.
      • et al.
      Low physical activity as a predictor for total and cardiovascular disease mortality in middle-aged men and women in Finland.
      • Barengo N.C.
      • Hu G.
      • Kastarinen M.
      • et al.
      Low physical activity as a predictor for antihypertensive drug treatment in 25-64-year-old populations in eastern and south-western Finland.
      • Hu G.
      • Sarti C.
      • Jousilahti P.
      • et al.
      Leisure time, occupational, and commuting physical activity and the risk of stroke.
      • Wennberg P.
      • Lindahl B.
      • Hallmans G.
      • et al.
      The effects of commuting activity and occupational and leisure time physical activity on risk of myocardial infarction.
      • Hu G.
      • Tuomilehto J.
      • Borodulin K.
      • Jousilahti P.
      The joint associations of occupational, commuting, and leisure-time physical activity, and the Framingham risk score on the 10-year risk of coronary heart disease.
      • Hu G.
      • Jousilahti P.
      • Borodulin K.
      • et al.
      Occupational, commuting and leisure-time physical activity in relation to coronary heart disease among middle-aged Finnish men and women.
      • Hu G.
      • Jousilahti P.
      • Antikainen R.
      • Tuomilehto J.
      Occupational, commuting, and leisure-time physical activity in relation to cardiovascular mortality among Finnish subjects with hypertension.
      • Wang Y.
      • Tuomilehto J.
      • Jousilahti P.
      • et al.
      Occupational, commuting, and leisure-time physical activity in relation to heart failure among Finnish men and women.
      • Ming Wen L.
      • Rissel C.
      Inverse associations between cycling to work, public transport, and overweight and obesity: findings from a population based study in Australia.
      • Hayashi T.
      • Tsumura K.
      • Suematsu C.
      • et al.
      Walking to work and the risk for hypertension in men: the Osaka Health Survey.
      • Hu G.
      • Pekkarinen H.
      • Hänninen O.
      • Tian H.
      • Guo Z.
      Relation between commuting, leisure time physical activity and serum lipids in a Chinese urban population.
      • Hu G.
      • Pekkarinen H.
      • Hänninen O.
      • et al.
      Commuting, leisure-time physical activity, and cardiovascular risk factors in China.
      • Gordon-Larsen P.
      • Nelson M.C.
      • Beam K.
      Associations among active transportation, physical activity, and weight status in young adults.
      • Gordon-Larsen P.
      • Boone-Heinonen J.
      • Sidney S.
      • et al.
      Active commuting and cardiovascular disease risk: the CARDIA study.
      evaluated walking or bicycling to work or school and therefore fail to capture populations that are unemployed, do not attend school, or use active transportation for purposes other than commuting. Given these limitations, there is need for better understanding of the potential health benefits of active transportation in U.S. adults.
      It was hypothesized that engaging in active transportation would be inversely associated with selected cardiovascular disease risk factors, independent of time spent in leisure-time and occupational physical activity. Because the greatest health benefits of physical activity accrue to sedentary individuals, it also was hypothesized that the associations would be stronger among individuals who did not meet physical activity recommendations through leisure-time and occupational physical activity.

      Methods

      Sample

      The study employed a cross-sectional design using data from the 2007–2008 and 2009–2010 cycles of the National Health and Nutrition Examination Survey (NHANES), a stratified multistage probability sample of the non-institutionalized U.S. civilian population. Details of the complex survey design are described elsewhere.
      CDC
      National Health and Nutrition Examination Survey homepage.
      Individuals aged ≥20 years who participated in both the questionnaire and Mobile Examination Center portions of the survey, were not pregnant, and did not report impaired mobility were included in the analysis. Impaired mobility was defined as using special equipment to walk or reporting much difficulty walking or being unable to walk one-quarter mile or up ten steps.

      Measures

      Outcomes of interest were cardiovascular disease risk factors for which physical activity has well-established protective effects, including BMI,
      • Hankinson A.L.
      • Daviglus M.L.
      • Bouchard C.
      • et al.
      Maintaining a high physical activity level over 20 years and weight gain.
      • Slentz C.A.
      • Duscha B.D.
      • Johnson J.L.
      • et al.
      Effects of the amount of exercise on body weight, body composition, and measures of central obesity: STRRIDE—a randomized controlled study.
      abdominal waist circumference,
      • Hankinson A.L.
      • Daviglus M.L.
      • Bouchard C.
      • et al.
      Maintaining a high physical activity level over 20 years and weight gain.
      • Slentz C.A.
      • Duscha B.D.
      • Johnson J.L.
      • et al.
      Effects of the amount of exercise on body weight, body composition, and measures of central obesity: STRRIDE—a randomized controlled study.
      hypertension,
      • Whelton S.P.
      • Chin A.
      • Xin X.
      • He J.
      Effect of aerobic exercise on blood pressure: a meta-analysis of randomized, controlled trials.
      diabetes,
      • Knowler W.C.
      • Barrett-Connor E.
      • Fowler S.E.
      • et al.
      Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin.
      • Hu G.
      • Lindstrom J.
      • Valle T.T.
      • et al.
      Physical activity, body mass index, and risk of type 2 diabetes in patients with normal or impaired glucose regulation.
      and high-density lipoprotein (HDL) level.
      • Kodama S.
      • Tanaka S.
      • Saito K.
      • et al.
      Effect of aerobic exercise training on serum levels of high-density lipoprotein cholesterol: a meta-analysis.
      BMI and abdominal waist circumference were treated as continuous variables; hypertension, diabetes, and HDL level were treated as dichotomous variables. Hypertension was defined as either self-reported use of pharmacologic therapy for high blood pressure, mean systolic blood pressure (SBP) ≥140 mmHg, or mean diastolic blood pressure (DBP) ≥90.
      • Ford E.S.
      • Zhao G.
      • Li C.
      • Pearson W.S.
      • Mokdad A.H.
      Trends in obesity and abdominal obesity among hypertensive and nonhypertensive adults in the United States.
      • Zhao G.
      • Ford E.S.
      • Li C.
      • et al.
      Independent associations of serum concentrations of 25-hydroxyvitamin D and parathyroid hormone with blood pressure among U.S. adults.
      Diabetes was defined as either self-reported use of pharmacologic therapy for diabetes or a hemoglobin A1c (HbA1c) ≥6.5%.
      The International Expert Committee
      International Expert Committee report on the role of the A1C assay in the diagnosis of diabetes.
      Low HDL was defined as a serum HDL level <40 mg/dL.
      Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults
      Executive summary of the third report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III).
      The primary independent variable was time spent in active transportation in a typical week. Participants were asked if they “walk or use a bicycle for at least 10 minutes continuously to get to and from places.” If they responded affirmatively, they were asked on how many days in a typical week and for how many minutes on a typical day. Individuals who did not engage in active transportation were considered to have 0 minutes/week. For all others, minutes/week of active transportation were calculated by multiplying the minutes/day spent walking or bicycling for transportation by the number of days/week on which the activity was reported. Time spent in active transportation was categorized into three levels: none (0 minutes/week); low (1–149 minutes/week); or high (≥150 minutes/week). The cutoff reflects current recommendations for a minimum of 150 minutes/week of moderate physical activity and represented the approximate median of the distribution of those with nonzero values for time spent in active transportation.
      Minutes per week of time spent in leisure-time physical activity and occupational physical activity were calculated using the same method. Because participants were asked independently about both moderate and vigorous leisure-time and occupational physical activity, time spent in vigorous activity was weighted by a factor of two in order to convert to moderate physical activity equivalents.
      • Tucker J.M.
      • Welk G.J.
      • Beyler N.K.
      Physical activity in U.S. adults: compliance with the Physical Activity Guidelines for Americans.
      Time spent in leisure-time and occupational physical activity were summed to create a single variable. This variable was then categorized into five levels: 0 minutes/week; 1–149 minutes/week; 150–449 minutes/week; 450–899 minutes/week; 900–2249 minutes/week; or ≥2250 minutes/week, with cutoffs based on approximate quintiles of those with nonzero values for time spent in combined leisure-time and occupational physical activity. NHANES uses the WHO's Global Physical Activity Questionnaire, which has been evaluated for reliability and validity.
      • Bull F.C.
      • Maslin T.S.
      • Armstrong T.
      Global Physical Activity Questionnaire (GPAQ): nine country reliability and validity study.
      Other covariates included age; gender; race/ethnicity (non-Hispanic white, non-Hispanic black, Mexican-American, or other); education level (<high school, high school, or >high school); and smoking status (never, former, current). Ratio of family income to the federal poverty level (<1, 1–2.9, ≥3),
      • Spatz E.S.
      • Canavan M.E.
      • Desai M.M.
      From here to JUPITER: identifying new patients for statin therapy using data from the 1999–2004 National Health and Nutrition Examination Survey.
      provided as a variable in the NHANES data set and used in prior studies of NHANES, was used to adjust for SES.

      Data Analyses

      First, descriptive statistics were used to characterize the sample by level of active transportation. Bivariate associations between sample characteristics and level of active transportation were examined using ANOVA and the χ2 test for continuous and categoric variables, respectively. Second, unadjusted associations between level of active transportation and each of the five cardiovascular disease risk factors of interest were examined using ANOVA and the χ2 test as appropriate.
      Next, adjusted analyses of associations between level of active transportation and the cardiovascular disease risk factors were performed using linear regression for continuous outcomes (BMI and waist circumference) and logistic regression for dichotomous outcomes (hypertension, diabetes, and low HDL). All multivariable models were adjusted for sociodemographic variables, smoking status, and time spent in combined leisure-time and occupational physical activity.
      Finally, in addition to analyses of the total sample, stratified analyses were conducted to assess whether associations between active transportation and cardiovascular disease risk factors differed in those who did and did not meet physical activity recommendations (at least 150 minutes/week of moderate physical activity) through combined leisure-time and occupational physical activity. Stratified analyses were performed in order to evaluate active transportation in an otherwise relatively sedentary population that, based on prior research,
      • Blair S.N.
      • Kampert J.B.
      • Kohl 3rd, H.W.
      • et al.
      Influences of cardiorespiratory fitness and other precursors on cardiovascular disease and all-cause mortality in men and women.
      experiences the greatest benefit from participating in physical activity. All analyses were weighted to account for the complex survey design and were conducted using SAS 9.2 and SAS-Callable SUDAAN 9.0.3. Analyses were conducted in 2011. The study was exempted from review by the Yale University Human Investigation Committee.

      Results

      The final analytic sample included 9933 participants, 43% of whom did not meet physical activity recommendations based on combined leisure-time and occupational physical activity. Overall, 76% of individuals did not walk or bike for more than 10 minutes continuously for transportation in a typical week (i.e., no active transportation), and 19% of individuals engaged in no physical activity of any form.
      Characteristics of the sample are shown in Table 1. Individuals who engaged in the highest level of active transportation, compared with those who engaged in no or low active transportation, were younger and more likely to be male, Mexican-American, lower income, and less than high-school educated. Level of active transportation was positively associated with time spent in combined leisure-time and occupational physical activity (Table 1). In unadjusted analyses, there were significant inverse associations of level of active transportation with mean BMI and mean abdominal waist circumference and with prevalence of both hypertension and diabetes (Table 2). No association was found between active transportation and prevalence of low HDL.
      Table 1Description of the sample, % unless otherwise noted
      CharacteristicTotal sample (N=9933)
      No active transportation (n=7284; 76%)Low active transportation (n=1129; 11%)High active transportation (n=1520; 14%)p-value
      For ANOVA or χ2 test
      Age (years; M±SE)46±0.343±0.842±0.6<0.001
      Gender0.001
       Male485155
      Race/ethnicity0.003
       Mexican-American121519
       Non-Hispanic white716560
       Non-Hispanic black101312
       Other688
      Education level<0.001
       <High school161828
       High school252217
       >High school596055
      Family income level, % FPL<0.001
       <100101520
       100 to <300313235
       ≥300514537
       Unknown898
      Smoking status0.038
       Never565556
       Former242321
       Current212223
      Time spent in combined leisure-time and occupational physical activity, minutes per week<0.001
       None262326
       1–14913146
       150–449201715
       500–899141515
       900–2249161820
       ≥2250121319
      Note: All ns are unweighted and percentages are weighted; percentages may not sum to 100% because of rounding. No active transportation=0 minutes/week; low active transportation=1–149 minutes/week; high active transportation≥150 minutes/week.
      FPL, federal poverty level
      a For ANOVA or χ2 test
      Table 2Unadjusted and adjusted
      Adjusted for age, gender, race/ethnicity, education level, income, smoking status, and combined leisure-time and occupational physical activity
      associations between level of active transportation and cardiovascular disease risk factors in unstratified and stratified
      Stratified by whether participants did or did not obtain ≥150 minutes/week of combined leisure-time and occupational physical activity
      analyses
      Level of active transportationBMIWaist circumference, cmHypertensionDiabetesLow HDL
      UnadjustedAdjusted β (95% CI)UnadjustedAdjusted β (95% CI)UnadjustedAOR (95% CI)UnadjustedAOR (95% CI)UnadjustedAOR (95% CI)
      M±SEp-value
      p-value for ANOVA or χ2 test
      M±SE (cm)p-value
      p-value for ANOVA or χ2 test
      %±SEp-value
      p-value for ANOVA or χ2 test
      %±SEp-value
      p-value for ANOVA or χ2 test
      %±SEp-value
      p-value for ANOVA or χ2 test
      UNSTRATIFIED<0.001<0.0010.767
      All included participants<0.001<0.00130.3±0.91 (ref)8.9±0.41 (ref)21.3±0.71 (ref)
       None28.6±0.11 (ref)97.9±0.31 (ref)22.5±1.70.76 (0.61, 0.94)6.5±0.70.77 (0.58, 1.02)20.0±1.90.88 (0.67, 1.15)
       Low27.6±0.2−0.93 (−1.35, −0.51)95.2±0.6−2.22 (−3.25, −1.19)20.2±1.50.69 (0.58, 0.83)5.8±0.60.69 (0.54, 0.88)21.7±1.40.88 (0.73, 1.06)
       High27.3±0.3−1.24 (−1.68, −0.79)94.3±0.8−3.08 (−4.28, −1.89)<0.0010.0020.438
      STRATIFIED36.3±1.11 (ref)12.3±0.81 (ref)21.2±1.11 (ref)
      Did not meet physical activity recommendations<0.001<0.00128.3±2.70.75 (0.57, 0.98)9.7±1.10.83 (0.64, 1.07)18.2±2.40.76 (0.53, 1.11)
       None29.3±0.21 (ref)99.5±0.41 (ref)23.2±1.90.58 (0.44, 0.76)7.8±1.00.62 (0.45, 0.87)19.9±2.20.77 (0.57, 1.05)
       Low27.8±0.4−1.48 (−2.34, −0.61)95.3±0.9−3.78 (−5.65, −1.90)<0.0010.0170.846
       High27.6±0.4−1.73 (−2.47, −0.99)94.4±1.0−5.04 (−6.82, −3.26)26.5±1.31 (ref)6.8±0.41 (ref)21.3±0.81 (ref)
      Met physical activity recommendations0.0110.00719.0±2.10.77 (0.58, 1.02)4.6±1.00.71 (0.41, 1.24)21.1±2.40.94 (0.68, 1.32)
       None28.1±0.11 (ref)96.9±0.31 (ref)18.7±1.90.77 (0.59, 1.02)4.9±0.80.73 (0.52, 1.03)22.5±2.10.94 (0.73, 1.20)
       Low27.5±0.3−0.64 (−1.30, 0.02)95.0±0.7−1.32 (−2.71, 0.07)
       High27.2±0.3−1.02 (−1.62, −0.42)94.2±1.0−2.17 (−3.74, −0.59)
      Note: Active transportation: none=0 minutes/week; low=1–149 minutes/week; high=≥150 minutes/week.
      HDL, high-density lipoprotein
      a Adjusted for age, gender, race/ethnicity, education level, income, smoking status, and combined leisure-time and occupational physical activity
      b Stratified by whether participants did or did not obtain ≥150 minutes/week of combined leisure-time and occupational physical activity
      c p-value for ANOVA or χ2 test
      After adjustment for all covariates, mean BMI remained lower among individuals with low (−0.9, 95% CI= −1.4, −0.5) and high (−1.2, 95% CI= −1.7, −0.8) levels of active transportation versus no active transportation (Table 2). Similarly, mean abdominal waist circumference remained lower among those engaged in low (−2.2 cm, 95% CI= −3.2, −1.2) and high (−3.1 cm, 95% CI= −4.3, −1.9) levels of active transportation versus no active transportation (Table 2). The odds of having hypertension were 24% lower (AOR=0.76, 95% CI=0.61, 0.94) and 31% lower (AOR=0.69, 95% CI=0.58, 0.83) among individuals with low and high levels of active transportation, respectively, than individuals with no active transportation (Table 2). Compared with no active transportation, high active transportation was associated with 31% lower odds of having diabetes (AOR=0.69, 95% CI=0.54, 0.88); the odds of having diabetes among individuals with low active transportation also were reduced, but did not reach significance (Table 2).
      Similar patterns were observed in stratified multivariable analyses (Table 2). Within the group that did not meet physical activity recommendations through combined leisure-time and occupational physical activity, increasing active transportation was associated with lower mean BMIs, smaller waist circumferences, and lower odds of both hypertension and diabetes. Further, even among the group that did meet physical activity recommendations through combined leisure-time and occupational physical activity, engaging in a high level of active transportation was associated with a lower mean BMI and smaller mean waist circumference. However, the magnitudes of these associations were smaller than those seen in the former group.

      Discussion

      Less than one quarter of U.S. adults in a nationally representative sample reported walking or bicycling for transportation in a typical week. After adjusting for potential confounders, engaging in active transportation was associated with lower BMI, smaller waist circumference, and lower odds of hypertension and diabetes. Based on the CIs, there were no differences between the associations of low and high levels of active transportation with the outcomes of interest. However, there was a trend toward higher levels of active transportation having stronger inverse associations with these four cardiovascular disease risk factors. After stratification of the sample into those who did or did not meet physical activity recommendations through a combination of leisure-time and occupational physical activity, the magnitudes of the associations were larger among the more sedentary group. However, even those who met physical activity recommendations had a significantly lower mean BMI and lower mean waist circumference when they also engaged in high levels of active transportation.
      The present study's findings are interesting in light of evidence that fitness may be a more important determinant of cardiovascular risk than adiposity.
      • Wei M.
      • Kampert J.B.
      • Barlow C.E.
      • et al.
      Relationship between low cardiorespiratory fitness and mortality in normal-weight, overweight, and obese men.
      Although use of continuous and dichotomous dependent variables precludes direct comparison, the magnitude of associations between active transportation and BMI and waist circumference appeared small relative to its associations with hypertension and diabetes. Prior studies have demonstrated that fitness is associated with reductions in blood pressure
      • Whelton S.P.
      • Chin A.
      • Xin X.
      • He J.
      Effect of aerobic exercise on blood pressure: a meta-analysis of randomized, controlled trials.
      • Lee D.
      • Sui X.
      • Church T.S.
      • et al.
      Changes in fitness and fatness on the development of cardiovascular disease risk factors: hypertension, metabolic syndrome, and hypercholesterolemia.
      and improved glycemic control
      • Boulé N.G.
      • Haddad E.
      • Kenny G.P.
      • Wells G.A.
      • Sigal R.J.
      Effects of exercise on glycemic control and body mass in type 2 diabetes mellitus: a meta-analysis of controlled clinical trials.
      independent of its effect on adiposity. No association was observed between active transportation and low HDL. Active transportation may not be of sufficient intensity to raise HDL levels.
      • Kraus W.E.
      • Houmard J.A.
      • Duscha B.D.
      • et al.
      Effects of the amount and intensity of exercise on plasma lipoproteins.
      Active transportation is an untapped reservoir of opportunity for physical activity for many U.S. adults. A study using the National Household Transportation Survey found similar low utilization of active transportation, with only 19% of Americans aged ≥5 years reporting walking or bicycling for transportation.
      • Pucher J.
      • Buehler R.
      • Merom D.
      • Bauman A.
      Walking and cycling in the U.S., 2001–2009: evidence from the National Household Travel Surveys.
      In contrast to the U.S., many European countries experience high population levels of active transportation.
      • Pucher J.
      • Buehler R.
      • Bassett D.R.
      • Dannenberg A.L.
      Walking and cycling to health: a comparative analysis of city, state, and international data.
      In Germany, the proportion of individuals reporting any walking or cycling for transportation are two and seven times greater than in the U.S., respectively.
      • Buehler R.
      • Pucher J.
      • Merom D.
      • Bauman A.
      Active travel in Germany and the U.S.: contributions of daily walking and cycling to physical activity.
      These differences are in part due to policies, community planning, and infrastructure design that make active transportation appealing.
      • de Nazelle A.
      • Nieuwenhuijsen M.J.
      • Antó J.M.
      • et al.
      Improving health through policies that promote active travel: a review of evidence to support integrated health impact assessment.
      • Buehler R.
      • Pucher J.
      • Merom D.
      • Bauman A.
      Active travel in Germany and the U.S.: contributions of daily walking and cycling to physical activity.
      • Pucher J.
      • Buehler R.
      • Bassett D.R.
      • Dannenberg A.L.
      Walking and cycling to health: a comparative analysis of city, state, and international data.
      • Buehler R.
      Determinants of transport mode choice: a comparison of Germany and the USA.
      Implementing similar strategies in the U.S. could have important implications for individuals with time or financial constraints that prohibit leisure-time physical activity or with professions and work environments that are not conducive to occupational physical activity.
      Although the cross-sectional study design precludes inferring a causal effect of active transportation on the outcomes of interest, the findings are consistent with prior longitudinal studies that demonstrate dose-dependent reductions in cardiovascular disease risk factors associated with physical activity.
      • Slentz C.A.
      • Duscha B.D.
      • Johnson J.L.
      • et al.
      Effects of the amount of exercise on body weight, body composition, and measures of central obesity: STRRIDE—a randomized controlled study.
      • Whelton S.P.
      • Chin A.
      • Xin X.
      • He J.
      Effect of aerobic exercise on blood pressure: a meta-analysis of randomized, controlled trials.
      • Hu G.
      • Lindstrom J.
      • Valle T.T.
      • et al.
      Physical activity, body mass index, and risk of type 2 diabetes in patients with normal or impaired glucose regulation.
      • Warburton D.E.R.
      • Nicol C.W.
      • Bredin S.S.D.
      Health benefits of physical activity: the evidence.
      • Kelley G.A.
      • Kelley K.A.
      • Vu Tran Z.
      Aerobic exercise and resting blood pressure: a meta−analytic review of randomized, controlled trials.
      • Kelley G.A.
      • Kelley K.S.
      Aerobic exercise and HDL2-C: a meta-analysis of randomized controlled trials.
      The findings also are consistent with prior studies of U.S. adults that found inverse associations between active commuting and cardiovascular disease risk factors.
      • Gordon-Larsen P.
      • Nelson M.C.
      • Beam K.
      Associations among active transportation, physical activity, and weight status in young adults.
      • Gordon-Larsen P.
      • Boone-Heinonen J.
      • Sidney S.
      • et al.
      Active commuting and cardiovascular disease risk: the CARDIA study.
      This suggests a potential role for active transportation in risk factor modification. Increasing levels of active transportation may have additive health benefits for individuals who are already physically active. However, the greatest impacts could accrue to the sedentary, highest-risk populations that are most sensitive to barriers to engaging in other forms of physical activity. Collectively, these findings suggest that public policy and built environment interventions to increase levels of active transportation in the U.S. may be justified on the grounds of health promotion. Additionally, these strategies could help reduce morbidity and mortality linked to motor vehicle emissions, including cardiopulmonary disease
      • Grabow M.L.
      • Spak S.N.
      • Holloway T.
      • et al.
      Air quality and exercise-related health benefits from reduced car travel in the midwestern U.S..
      • Woodcock J.
      • Edwards P.
      • Tonne C.
      • et al.
      Public health benefits of strategies to reduce greenhouse-gas emissions: urban land transport.
      and global climate change.
      • Haines A.
      • Kovats R.
      • Campbell-Lendrum D.
      • Corvalan C.
      Climate change and human health: impacts, vulnerability, and mitigation.
      • Patz J.A.
      • Campbell-Lendrum D.
      • Holloway T.
      • Foley J.A.
      Impact of regional climate change on human health.

      Strengths and Limitations

      The present study has several strengths, including use of a sample representative of the U.S. adult population, assessment of active transportation for any purpose rather than just for commuting, use of objective measurements of cardiovascular disease risk factors, adjustment for contributions of other forms of physical activity, and a large sample size. Nonetheless, this study does have limitations. The cross-sectional design prohibits attributing causality to the associations between active transportation and investigated cardiovascular disease risk factors. However, excluding participants with impaired mobility reduced the potential for reverse causation; individuals with disabilities related to any of the outcomes of interest might not have been able to engage in active transportation (e.g., an individual with an amputation due to diabetes who, therefore, was unable to walk or bike without difficulty).
      Confounding could occur if individuals who engage in active transportation are more likely to make other healthy lifestyle choices. To address this possibility, time spent in non–active transportation physical activity and smoking status were included in multivariable models. The sample also was restricted to those who did not meet physical activity recommendations through combined leisure-time and occupational physical activity in the stratified analyses. Interestingly, there was evidence to refute a positive correlation between active transportation and other healthy behaviors.
      First, smoking status did not differ substantially across levels of active transportation. Second, analysis of data from the 2007–2008 NHANES cycle, which included information on self-reported diet quality, revealed no association between active transportation and diet quality (data not shown). Third, active transportation was more common among demographic groups that tend to engage in less leisure-time physical activity,
      CDC
      Prevalence of self-reported physically active adults—U.S., 2007.
      CDC
      Prevalence of regular physical activity among adults—U.S., 2001 and 2005.
      • Berrigan D.
      • Troiano R.P.
      • McNeel T.
      • DiSogra C.
      • Ballard-Barbash R.
      Active transportation increases adherence to activity recommendations.
      which may reflect their concentration in urban areas and lower rates of car access. These groups' high levels of combined leisure-time and occupational physical activity may be due to employment in more physically demanding professions.
      • Berrigan D.
      • Troiano R.P.
      • McNeel T.
      • DiSogra C.
      • Ballard-Barbash R.
      Active transportation increases adherence to activity recommendations.
      • Steele R.
      • Mummery K.
      Occupational physical activity across occupational categories.
      CDC
      Contribution of occupational physical activity toward meeting recommended physical activity guidelines: U.S., 2007.
      The analysis did not adjust for rural, suburban, or urban location or geographic region because of restricted access to geographic variables. Systematic differences in cardiovascular disease risk factor profiles by region or degree of rurality could have caused confounding if these geographic factors also influenced levels of active transportation (e.g., due to weather, cultural norms, or inconvenience). Additionally, time spent in physical activity was based on self-report, which is known to overestimate accelerometer-based measurements of physical activity.
      • Tucker J.M.
      • Welk G.J.
      • Beyler N.K.
      Physical activity in U.S. adults: compliance with the Physical Activity Guidelines for Americans.
      However, there is little reason to suspect systematic misreporting among certain groups that would lead to bias. It was not possible to estimate the intensity of active transportation without knowledge of the relative contribution of walking and biking to time spent in active transportation.

      Conclusion

      Evidence for the diverse health benefits associated with active transportation is mounting. Despite this knowledge, levels of active transportation in the U.S. remain low, largely because of policies and built environments that discourage its use. This study provides support for the value of active transportation in reducing the prevalence of important cardiovascular disease risk factors, including obesity, hypertension, and diabetes. Interventions to promote the use of active transportation in the U.S. should be pursued.
      Dr. Furie was supported by the Robert Wood Johnson Foundation Clinical Scholars Program and the Department of Veterans Affairs.
      No financial disclosures were reported by the authors of this paper.

      References

        • Tucker J.M.
        • Welk G.J.
        • Beyler N.K.
        Physical activity in U.S. adults: compliance with the Physical Activity Guidelines for Americans.
        Am J Prev Med. 2011; 40: 454-461
        • CDC
        Prevalence of self-reported physically active adults—U.S., 2007.
        MMWR Morb Mortal Wkly Rep. 2008; 57: 1297-1300
        • Hankinson A.L.
        • Daviglus M.L.
        • Bouchard C.
        • et al.
        Maintaining a high physical activity level over 20 years and weight gain.
        JAMA. 2010; 304: 2603-2610
        • Slentz C.A.
        • Duscha B.D.
        • Johnson J.L.
        • et al.
        Effects of the amount of exercise on body weight, body composition, and measures of central obesity: STRRIDE—a randomized controlled study.
        Arch Intern Med. 2004; 164: 31-39
        • Whelton S.P.
        • Chin A.
        • Xin X.
        • He J.
        Effect of aerobic exercise on blood pressure: a meta-analysis of randomized, controlled trials.
        Ann Intern Med. 2002; 136: 493-503
        • Knowler W.C.
        • Barrett-Connor E.
        • Fowler S.E.
        • et al.
        Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin.
        N Engl J Med. 2002; 346: 393-403
        • Hu G.
        • Lindstrom J.
        • Valle T.T.
        • et al.
        Physical activity, body mass index, and risk of type 2 diabetes in patients with normal or impaired glucose regulation.
        Arch Intern Med. 2004; 164: 892-896
        • Kodama S.
        • Tanaka S.
        • Saito K.
        • et al.
        Effect of aerobic exercise training on serum levels of high-density lipoprotein cholesterol: a meta-analysis.
        Arch Intern Med. 2007; 167: 999-1008
        • Blair S.N.
        • Kampert J.B.
        • Kohl 3rd, H.W.
        • et al.
        Influences of cardiorespiratory fitness and other precursors on cardiovascular disease and all-cause mortality in men and women.
        JAMA. 1996; 276: 205-210
        • Hamer M.
        • Chida Y.
        Active commuting and cardiovascular risk: a meta-analytic review.
        Prev Med. 2008; 46: 9-13
        • de Nazelle A.
        • Nieuwenhuijsen M.J.
        • Antó J.M.
        • et al.
        Improving health through policies that promote active travel: a review of evidence to support integrated health impact assessment.
        Environ Int. 2011; 37: 766-777
        • Buehler R.
        • Pucher J.
        • Merom D.
        • Bauman A.
        Active travel in Germany and the U.S.: contributions of daily walking and cycling to physical activity.
        Am J Prev Med. 2011; 41: 241-250
        • Wanner M.
        • Gotshci T.
        • Martin-Diener E.
        • Kahlmeier S.
        • Martin B.W.
        Active transport, physical activity, and body weight in adults: a systematic review.
        Am J Prev Med. 2012; 42: 493-502
        • Andersen L.B.
        • Schnohr P.
        • Schroll M.
        • Hein H.O.
        All-cause mortality associated with physical activity during leisure time, work, sports, and cycling to work.
        Arch Intern Med. 2000; 160: 1621-1628
        • Hu G.
        • Qiao Q.
        • Silventoinen K.
        • et al.
        Occupational, commuting, and leisure-time physical activity in relation to risk for type 2 diabetes in middle-aged Finnish men and women.
        Diabetologia. 2003; 46: 322-329
        • Hu G.
        • Eriksson J.
        • Barengo N.C.
        • et al.
        Occupational, commuting, and leisure-time physical activity in relation to total and cardiovascular mortality among Finnish subjects with type 2 diabetes.
        Circulation. 2004; 110: 666-673
        • Barengo N.C.
        • Hu G.
        • Lakka T.A.
        • et al.
        Low physical activity as a predictor for total and cardiovascular disease mortality in middle-aged men and women in Finland.
        Eur Heart J. 2004; 25: 2204-2211
        • Barengo N.C.
        • Hu G.
        • Kastarinen M.
        • et al.
        Low physical activity as a predictor for antihypertensive drug treatment in 25-64-year-old populations in eastern and south-western Finland.
        J Hypertens. 2005; 23: 293-299
        • Hu G.
        • Sarti C.
        • Jousilahti P.
        • et al.
        Leisure time, occupational, and commuting physical activity and the risk of stroke.
        Stroke. 2005; 36: 1994-1999
        • Wennberg P.
        • Lindahl B.
        • Hallmans G.
        • et al.
        The effects of commuting activity and occupational and leisure time physical activity on risk of myocardial infarction.
        Eur J Cardiovasc Prev Rehabil. 2006; 13: 924-930
        • Hu G.
        • Tuomilehto J.
        • Borodulin K.
        • Jousilahti P.
        The joint associations of occupational, commuting, and leisure-time physical activity, and the Framingham risk score on the 10-year risk of coronary heart disease.
        Eur Heart J. 2007; 28: 492-498
        • Hu G.
        • Jousilahti P.
        • Borodulin K.
        • et al.
        Occupational, commuting and leisure-time physical activity in relation to coronary heart disease among middle-aged Finnish men and women.
        Atherosclerosis. 2007; 194: 490-497
        • Hu G.
        • Jousilahti P.
        • Antikainen R.
        • Tuomilehto J.
        Occupational, commuting, and leisure-time physical activity in relation to cardiovascular mortality among Finnish subjects with hypertension.
        Am J Hypertens. 2007; 20: 1242-1250
        • Wang Y.
        • Tuomilehto J.
        • Jousilahti P.
        • et al.
        Occupational, commuting, and leisure-time physical activity in relation to heart failure among Finnish men and women.
        J Am Coll Cardiol. 2010; 56: 1140-1148
        • Ming Wen L.
        • Rissel C.
        Inverse associations between cycling to work, public transport, and overweight and obesity: findings from a population based study in Australia.
        Prev Med. 2008; 46: 29-32
        • Hayashi T.
        • Tsumura K.
        • Suematsu C.
        • et al.
        Walking to work and the risk for hypertension in men: the Osaka Health Survey.
        Ann Intern Med. 1999; 131: 21-26
        • Hu G.
        • Pekkarinen H.
        • Hänninen O.
        • Tian H.
        • Guo Z.
        Relation between commuting, leisure time physical activity and serum lipids in a Chinese urban population.
        Ann Hum Biol. 2001; 28: 412-421
        • Hu G.
        • Pekkarinen H.
        • Hänninen O.
        • et al.
        Commuting, leisure-time physical activity, and cardiovascular risk factors in China.
        Med Sci Sports Exerc. 2002; 34: 234-238
        • Gordon-Larsen P.
        • Nelson M.C.
        • Beam K.
        Associations among active transportation, physical activity, and weight status in young adults.
        Obesity. 2005; 13: 868-875
        • Gordon-Larsen P.
        • Boone-Heinonen J.
        • Sidney S.
        • et al.
        Active commuting and cardiovascular disease risk: the CARDIA study.
        Arch Intern Med. 2009; 169: 1216-1223
        • CDC
        National Health and Nutrition Examination Survey homepage.
        • Ford E.S.
        • Zhao G.
        • Li C.
        • Pearson W.S.
        • Mokdad A.H.
        Trends in obesity and abdominal obesity among hypertensive and nonhypertensive adults in the United States.
        Am J Hypertens. 2008; 21: 1124-1128
        • Zhao G.
        • Ford E.S.
        • Li C.
        • et al.
        Independent associations of serum concentrations of 25-hydroxyvitamin D and parathyroid hormone with blood pressure among U.S. adults.
        J Hypertens. 2010; 28: 1821-1828
        • The International Expert Committee
        International Expert Committee report on the role of the A1C assay in the diagnosis of diabetes.
        Diabetes Care. 2009; 32: 1327-1334
        • Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults
        Executive summary of the third report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III).
        JAMA. 2001; 285: 2486-2497
        • Bull F.C.
        • Maslin T.S.
        • Armstrong T.
        Global Physical Activity Questionnaire (GPAQ): nine country reliability and validity study.
        J Phys Act Health. 2009; 6: 790-804
        • Spatz E.S.
        • Canavan M.E.
        • Desai M.M.
        From here to JUPITER: identifying new patients for statin therapy using data from the 1999–2004 National Health and Nutrition Examination Survey.
        Circ Cardiovasc Qual Outcomes. 2009; 2: 41-48
        • Wei M.
        • Kampert J.B.
        • Barlow C.E.
        • et al.
        Relationship between low cardiorespiratory fitness and mortality in normal-weight, overweight, and obese men.
        JAMA. 1999; 282: 1547-1553
        • Lee D.
        • Sui X.
        • Church T.S.
        • et al.
        Changes in fitness and fatness on the development of cardiovascular disease risk factors: hypertension, metabolic syndrome, and hypercholesterolemia.
        J Am Coll Cardiol. 2012; 59: 665-672
        • Boulé N.G.
        • Haddad E.
        • Kenny G.P.
        • Wells G.A.
        • Sigal R.J.
        Effects of exercise on glycemic control and body mass in type 2 diabetes mellitus: a meta-analysis of controlled clinical trials.
        JAMA. 2001; 286: 1218-1227
        • Kraus W.E.
        • Houmard J.A.
        • Duscha B.D.
        • et al.
        Effects of the amount and intensity of exercise on plasma lipoproteins.
        N Engl J Med. 2002; 347: 1483-1492
        • Pucher J.
        • Buehler R.
        • Merom D.
        • Bauman A.
        Walking and cycling in the U.S., 2001–2009: evidence from the National Household Travel Surveys.
        Am J Public Health. 2011; 101: S310-S317
        • Pucher J.
        • Buehler R.
        • Bassett D.R.
        • Dannenberg A.L.
        Walking and cycling to health: a comparative analysis of city, state, and international data.
        Am J Public Health. 2010; 100: 1986-1992
        • Buehler R.
        Determinants of transport mode choice: a comparison of Germany and the USA.
        J Transp Geogr. 2011; 19: 644-657
        • Warburton D.E.R.
        • Nicol C.W.
        • Bredin S.S.D.
        Health benefits of physical activity: the evidence.
        CMAJ. 2006; 174: 801-809
        • Kelley G.A.
        • Kelley K.A.
        • Vu Tran Z.
        Aerobic exercise and resting blood pressure: a meta−analytic review of randomized, controlled trials.
        Prev Cardiol. 2001; 4: 73-80
        • Kelley G.A.
        • Kelley K.S.
        Aerobic exercise and HDL2-C: a meta-analysis of randomized controlled trials.
        Atherosclerosis. 2006; 184: 207-215
        • Grabow M.L.
        • Spak S.N.
        • Holloway T.
        • et al.
        Air quality and exercise-related health benefits from reduced car travel in the midwestern U.S..
        Environ Health Perspect. 2011; 120: 68-76
        • Woodcock J.
        • Edwards P.
        • Tonne C.
        • et al.
        Public health benefits of strategies to reduce greenhouse-gas emissions: urban land transport.
        Lancet. 2009; 374: 1930-1943
        • Haines A.
        • Kovats R.
        • Campbell-Lendrum D.
        • Corvalan C.
        Climate change and human health: impacts, vulnerability, and mitigation.
        Lancet. 2006; 367: 2101-2109
        • Patz J.A.
        • Campbell-Lendrum D.
        • Holloway T.
        • Foley J.A.
        Impact of regional climate change on human health.
        Nature. 2005; 438: 310-317
        • CDC
        Prevalence of regular physical activity among adults—U.S., 2001 and 2005.
        MMWR Morb Mortal Wkly Rep. 2007; 56: 1209-1212
        • Berrigan D.
        • Troiano R.P.
        • McNeel T.
        • DiSogra C.
        • Ballard-Barbash R.
        Active transportation increases adherence to activity recommendations.
        Am J Prev Med. 2006; 31: 210-216
        • Steele R.
        • Mummery K.
        Occupational physical activity across occupational categories.
        J Sci Med Sport. 2003; 6: 398-407
        • CDC
        Contribution of occupational physical activity toward meeting recommended physical activity guidelines: U.S., 2007.
        MMWR Morb Mortal Wkly Rep. 2011; 60: 656-660