Prevalence of overweight/obesity and its association with sedentary behavior in children

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Revista

Portuguesa

de

Cardiologia

Portuguese

Journal

of

Cardiology

www.revportcardiol.org

ORIGINAL

ARTICLE

Prevalence

of

overweight/obesity

and

its

association

with

sedentary

behavior

in

children

Catarina

Vasques

a,∗

_,

_Maria

_Mota

b

_,

_Teresa

_Correia

c

_,

_Vítor

_Lopes

a

a_Research_Center_in_Sports_Sciences,_Health_Sciences_and_Human_Development,_Polytechnic_Institute_of_Braganc_¸a,_Department ofSportsScience,Braganc¸a,Portugal

b_Research_Center_in_Sports_Sciences,_Health_Sciences_and_Human_Development,_University_of_{Trás-os-Montes}_and_Alto_Douro, SchoolofHealth,Braganc¸a,Portugal

c_Research_Center_in_Sports_Sciences,_Health_Sciences_and_Human_Development,_Polytechnic_Institute_of_Braganc_¸a,_School ofHealth,Braganc¸a,Portugal

Received26January2012;accepted18March2012 Availableonline13November2012

KEYWORDS

Bodymassindex; Riskfactors; Sedentarylifestyle

Abstract

Objective: Theaimofthisstudywastodeterminetheprevalenceofoverweightandobesity inchildreninthenortheastregionofPortugal,andtoexamineitsassociationwithsedentary behavior.

Methods:Datawerecollectedon1786children(907boys,879girls)aged6to13years.Body massindexwascalculatedfrommeasuredheightandweight(weightinkg/heightinmsquared). Overweight andobesity were determined usingthe InternationalObesity Task Forcecutoff values.Sedentarybehaviorwasassessedbasedonmeansoftransporttoandfromschooland timespentwatchingTVandplayingvideogames(TVPC).

Results:The prevalences ofoverweight andobesitywere 22.6% and9.4%respectively. The differencesbetweenthesexesforbothoverweightandobesitywerenotsigniﬁcant.Mostof thechildren (78.4%)go toschoolby car.Boys spendmoretimeonTVPCthangirls, bothon weekdaysandonweekends.Thelogisticregressionmodelindicatedasigniﬁcanteffectof1.5 hoursofTVPCbyboysduringweekdays(OR=0.246;p=0.015).Boyswhospentlessthan1.5hours onweekdaysonTVPCwere75.4%lesslikelytobeoverweightthanthosewhospentmorethan 1.5hours.

Conclusion: Theprevalenceofoverweight andobesitywas 32%.Only12.2% ofthechildren spendlessthan1.5hoursonTVPC.Boyswhospendlessthan1.5hoursonTVPCare75.4%less likelytobeoverweight/obesethanthosewhospendmorethan1.5hours.

∗_{Corresponding}_author.

E-mailaddress:catarinav@ipb.pt(C.Vasques).

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PALAVRAS-CHAVE Índicedemassa corporal; Fatoresderisco; Estilodevida sedentário

Prevalênciadesobrepeso/obesidadeemcrianc¸aseasuaassociac¸ão

comcomportamentossedentários

Resumo

Objectivo:determinaraprevalênciadesobrepeso/obesidadeemcrianc¸asdaregiãoNordeste dePortugal,eanalisarsuaassociac¸ãocomosedentarismo.

Métodos: Osdadosforamrecolhidosem1786crianc¸as(n=907meninos,meninasn=879)com idadesentreos6e13 anos,oíndicedemassacorporalfoicalculadoapartirdaestaturae peso[massacorporal(kg)/Altura(m2)]medidos.Osobrepeso/obesidadeforamdeterminados usandoosvaloresdecortedaIOTF.Ocomportamentosedentáriofoiavaliadotendoemconta: omeiodetransporteetempogastoavertelevisão/jogarvideojogos(TVPC).

Resultados: aprevalênciadesobrepeso/obesidade foide 22,6%e 9,4%,respetivamente.As diferençasentreossexos,tantoparaosobrepesocomoparaaobesidade,nãoforam significa-tivas.Amaioriadascriançasusaoautomóvel(78,4%)parairàescola.Osmeninosgastarammais tempoemTVPCqueasmeninas,tantoduranteasemanacomonosfinsdesemana.Omodelo deregressãologísticaindicouumefeitosignificativode1,5horasdeTVPCpara osmeninos, duranteasemana(OR=0,246;p=0,015).Osmeninosquegastarammenosde1,5horasdurante asemanaemactividadesTVPCforam75,4%menospropensosaseremobesosdoqueaqueles quegastarammaisde1,5horas.

Conclusão:aprevalênciadesobrepeso/obesidadeatinge32%.Apenas12,2%gastammenosde 1,5horasemTVPC. Osmeninosque passammenosde 1,5horasem TVPCsão75,4% menos propensosatersobrepeso/obesidadedoqueaquelesquegastammaisde1,5horas.

Introduction

A majority of western countries and those undergoing economic transition have experienced an increase in the prevalenceofchildhoodobesity.1_As_long_ago_as_1997, obe-sitywasidentiﬁedasapublichealthprobleminbothadults andyouth.2

There is a large group of chronic diseases asso-ciated with obesity, including cardiovascular disease, diabetes, and hypertension.3,4 _The _main _causes _of obe-sityarelow levelsofdaily physical activityand excessive intake of high-calorie food,5 _leading _to _imbalances _that increase body fat mass. The problem has several dimen-sions,includingbiological,socialandpsychosocialaspects, and affects all age ranges, genders and socioeconomic levels.6

Several studies conducted in Portugal7---9 _in _children aged between 3 and 14 reveal the extent of the prob-lem.Apartfromthebiologicalandculturalcharacteristics of the samples, the prevalence of overweight ranged between 13% and 30%, and the prevalence of obesity was 4---14%. These studies also indicated that females ---adults and children --- are more affected by this epi-demic.

Despitethisnationaltrend,thesituationinthenortheast regionofPortugalisstillunknown.Thus,themaingoalof thisstudywastodeterminetheprevalence ofoverweight andobesityanditsassociation withsedentary behaviorin children of the northeast region of Portugal, as assessed by the type of transportation used between school and homeandtimespentwatchingTVandplayingvideogames (TVPC).

Methods

Population

Thesampleconsistedof1786subjects---879femaleand907 male---agedbetween 6and 13years.This number corre-spondstoallchildrenattendingpublicschoolsinthetowns of Braganc¸a andMacedodeCavaleirosin thenortheastof Portugal. Onlychildren who didnot attend schoolon the daysofdatacollectionwerenotincluded.

The data were collected during the 2008 school year. Authorization was obtained from the Executive Board of each school and informed consent was obtained from all childrenandtheirparents.Thestudywasapprovedbylocal educationauthoritiesandtheethicscommitteeofthe Poly-technicInstituteofBraganc¸a.

Heightandweightassessment

Allindividualswereassessedwithoutshoesandwith mini-malclothing(T-shirtandshorts).ASECAscale,model885, wasusedtomeasureweight,and thevalue wasrecorded inkilogramswithapproximationtohectograms.Heightwas measuredusingawall-mountedstadiometer;theresultwas recordedincentimeters.

Bodymassindex(BMI)(weightinkg/heightinmsquared) was calculated and the International Obesity Task Force (IOTF) cut-off values12 _for _overweight _and _obesity _were used.

Assessmentofsedentarybehaviors

Allindividualsinthesampleansweredaquestionnaireabout their travelto and from school (whether theywalked or

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Table1 Meanvaluesandstandarddeviationsofweight(kg),height(cm)andBMI(kg/m2₎_in_the_study_population,_by_gender

andage.

Age(years) Girls Boys

n Weight Height BMI n Weight Height BMI

6 98 26.0±5.4 122.0±4.7 17.4±3.0 77 26.1±4.9 122.0±5.3 17.4±2.4 7 137 28.0±5.8 126.7±4.9 17.4±3.0 149 28.0±5.3 127.9±5.6 17.0±2.4 8 127 31.2_±5.9 132.1_±5.7 17.8_±2.7 131 32.4_±6.5 133.1_±6.3 18.1_±2.7 9 135 35.0±8.1 137.7±6.5 18.3±3.3 130 35.2±6.8 137.2±6.1 18.6±2.8 10 125 39.7_±8.4 143.7_±7.3 19.1_±3.1 138 39.7_±7.7 142.6_±7.7 19.4_±3.5 11 137 45.8±10.3 150.3±8.1 20.1±3.6 154 43.2±11.2 148.1±7.4 19.5±4.0 12 79 48.0_±9.1 154.0_±6.4 20.1_±3.0 93 48.8_±10.4 154.2_±7.1 20.5_±3.8 13 40 54.9±12.6 157.7±6.3 21.9±4.1 31 50.1±10.8 160.0±9.0 19.4±3.1

cycledorwent bycarorbus) andthetimetheyspent,in hoursduringweekdaysandonweekends,watching televi-sion and playing video games (TVPC). The children were helped by the researchteam tocomplete their question-naires.

Statisticalanalysis

First,anexploratorydataanalysiswascarriedoutto iden-tifypossibleerrorsintheinformationinput,thepresenceof outliersandthenormalityofthedistributions.

Descriptivestatisticswerecalculatedforweight,height andBMI(meanandstandarddeviations).Apercentage anal-ysiswasalsocarriedoutonthetransportationusedandthe numberofhoursofTVPCuse.

As the variablesdidnot present normalityintheir dis-tributions,theKruskal---Wallistestwasusedtoanalyzethe differencesbetweenagegroupsandsexes.

To estimatetheassociationof TVPCandtransportused with overweight and obesity, logistic regression was usedseparatelyfor eachgender while controllingtheage effecttoobtainadjustedoddratios(OR).Forthispurpose, theTVPCvariablewascategorizedaccordingtothenumber ofhoursspentduringweekdaysandonweekends(upto1.5; 2.5;3.5;4.5;5.5;6.5and7.5hours).

Thesigniﬁcancelevelwasdeﬁnedasp≤0.05.

Results

Table 1 presents the descriptive statistics (mean and standard deviation) of the population characteristics (weight,heightandBMI)byagesandgender.

Figure1presentstheprevalencesofoverweightand obe-sity according togender and age. The prevalences in the

overall population were respectively 22.6% and 9.4%. In boys,theprevalenceofoverweightwas23.2%andofobesity was8.7%.Ingirls,theprevalenceofoverweightwas22.1% andofobesitywas10.0%(Figure1).

Althoughtherewerenosigniﬁcantdifferencesbetween thesexes in overweightand obesity,there wasa general tendencyinboystohavehigheroverweightprevalenceatall ages,exceptattheagesof10,11and13years.Forobesity theconversewasseen;girlshadhighervaluesthanboysat allages,exceptattheagesof10,11and12years.

Nosigniﬁcantdifferenceswereobservedbetweenagesin overweightandobesity,buttherewasalowerprevalenceof obesityinoldersubjects.Regardingoverweight,thevalues wereverycloseatallages.

Thepercentagesbygenderandageofchildrenwhogoto andfromschoolbycarversusthosewhowalkor cycleare presentedinFigure2.

Car or buswasthe means oftransport for 78.4%.Only 21.6%ofthe childrenwalkedtoandfromschool.The car wasalsothe mostcommonmeans of transportinat least oneofthedailyjourneystoschool(56.3%).Thedifferences between thesexes werenot signiﬁcant. Walking wasless commoninbothsexes:10.3%ofgirlsand11.3%ofboys.

Analysisof thedifferencebetween agesinthe typeof transportationtoandfromschoolindicates signiﬁcant dif-ferencesbetween agesonly whentheyusethesametype of transportation both to and from school (chi-square(7)

Z=14.688;p=0.040).Olderchildrenlessfrequentlytraveled bycar.

Figure3presentsby ageandgender themeannumber ofhourschildrenspenteachweekdayandonweekendson TVPC.

Duringtheweek,themeanvalueswerelower,especially forboys(3.06hoursforgirlsand3.64hoursforboys),than ontheweekend(3.50hoursforgirlsand4.44hoursforboys).

Obesity 30% 20% 10% 0% Girls Boys Age (years) Prevalence Overweight 30% 20% 10% 0% Girls Boys Age (years) Prevalence 6 7 8 9 10 11 12 13 6 7 8 9 10 11 12 13

Figure1 Prevalenceofoverweightandobesityinthestudypopulation,accordingtotheInternationalObesityTaskForcevalues,10

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Girls 0% 20% 40% 60% 80% 100% Boys Pre v a lence 0% 20% 40% 60% 80% 100% Pre v a lence 6 Age (years) 7 8 9 10 11 12 13 6 Age (years) 7 8 9 10 11 12 13 car car/walk walk car car/walk walk

Figure2 Percentagesofchildrenwhogobycar(car)orwalk(walk)toandfromschool,orgotoschoolbycarandwalkhome (car/walk),bygenderandage.

Age (years) TVPC (hours) TVPC (hours) Weekdays Weekends 6 8 6 4 2 0 8 6 4 2 0 7 8 9 10 11 12 13 Girls Boys Girls Boys Age (years) 6 7 8 9 10 11 12 13

Figure3 Meannumberofhoursspentwatchingtelevisionandplayingvideogamesonweekdaysandweekends,bygenderand age.

Boysspentsigniﬁcantlymoretimethangirlsinsedentary activities(TVPC),bothonweekdays(chi-square(1)Z=11.647;

p=0.001)andonweekends(chi-square(1)Z=7.817;p=0.005).

Older children spent signiﬁcantly more time than younger children on TVPC both during weekdays (chi-square(7)Z=30.740;p=0.000)andonweekends(chi-square(7)

Z=25.495;p=0.001),with theexception of seven-year-old childrenonweekends.

Consideringtheoverallpopulation,only12.2%ofchildren spentlessthan1.5hoursonTVPC,whetheronweekdaysor onweekends.

The logisticregressionmodel didnotindicatea signiﬁ-canteffectofthe‘‘transport’’variable;itonlyindicateda signiﬁcanteffectof1.5hoursofTVPCbyboysonweekdays (OR=0.246;p=0.015),whichmeansthatboyswhospentless than1.5hoursonweekdayswatching televisionorplaying videogameswere75.4%lesslikelytobeoverweight/obese thanthosewhospentmorethan1.5hours.

Discussion

Theaimof thisstudywastodeterminethe prevalenceof overweightandobesityrelatedtosedentarybehaviorin chil-drenfromthenortheastregionofPortugal,namelythetype oftransportationtoandfromschoolandtimespent watch-ingtelevisionandplayingvideo games.The prevalenceof overweightandobesitywasdeterminedthroughBMI,using theIOTFreferencevalues.10

Thesamplewasnotrandom,andnoattemptwasmade toﬁnda representativesample ofchildren in the region; theintentionwasrathertoevaluateallchildrenaged6to 13attending publicschools in the towns of Braganc¸aand Macedo de Cavaleiros. Only children who did not attend schoolonthedaysofdatacollectionwerenotincluded.

The prevalences of overweight and obesity in children inthisregionofPortugalwere22.6%and9.4%,respectively. Theseresultsareinagreementwiththosefromotherstudies

carried out in Portugal11,12 _that _indicate _a _prevalence _of overweightandobesityofaround30%.

Somestudies13,14 _indicate _a_higher _prevalence _of over-weightandobesityinfemalesthaninmales.Inthepresent study, girls had a higherprevalence of obesity than boys at almost all ages,but the prevalence of overweightwas higherinboysthaningirls,althoughthedifferencewasnot signiﬁcant.

Thisstudy analyzedthe timespentwatching television andplaying videogames andthemeans oftransportused toandfromschool.Asexpected,childrenspentmoretime watching televisionand playingvideo gamesonweekends thanonweekdays.Boysspentmoretimeinbothcasesthan girls,andyoungerchildrenofbothsexesspentlesstimethan olderonesintheseactivities.

Asedentary lifestyleasidentiﬁed inthis study corrob-orates the ﬁndings of other studies,15,16 _particularly _with regardtotheimportanceofinactivityasariskfactor asso-ciatedwithobesityinchildren.

An association between excess weight and sedentary activitiessuchaswatchingtelevisionhasbeenreportedin numerous studies.17,18 _In_fact, _screen _time_competes_with physicalactivitytime,19 _leading_to_reduced_levels_of exer-ciseinchildren.20,21_Besides_the_association_between_screen timeandoverweight/obesity,foodintakeduringthisactivity canmakethisassociationevenmoresigniﬁcant.22

Inyoungerchildren,overweight/obesityseemsto aggre-gate in families.23 _The _daily _pattern _of _parents’ _physical inactivityandactivitycaninﬂuencetheirchildren’s behav-ior. At olderages,aschildrenbecome moreindependent, theirchoicesareoftenmoreinﬂuencedbytheirpeersthan bytheirparents.24

Televisionviewingisfrequently usedasanindicator of inactivityin epidemiologicandinterventionstudies.25 _This parametercorrelatesstronglywithobesityinchildhood.26,27 Inourstudy,thiscorrelationwasalsoidentiﬁedinboys.A signiﬁcant effect of 1.5hours of TVPC wasobserved dur-ingweekdays,withboyswhospendlessthan1.5hourson

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weekdayswatchingtelevisionandplayingvideogamesbeing 75.4% less likelyto be overweight/obese than those who spendmorethan1.5hours.Withgirls,nosuchassociation wasobserved.

Twomainexplanationsmaybeadvancedforthisresult: (1) girlsusually spend theirleisure time in activities that requirelowerenergyexpenditurethanboys,28_contributing tothehigherincidenceofobesityingirls;and(2)although themain sedentary behaviorscitedin theliterature were assessed,otherhabits,possiblymorecloselyrelatedtogirls’ choices,werenotconsideredinthisstudy.Soproblemswith assessmentoftotalsedentarybehaviorsmayexplainwhy,in thisstudy,girlsseemtobelessinactivebutaremoreoften obese.

Sincechildrenspendsomuchtimeplayingvideogames, it would be helpful for parents and educators toprovide childrenwithinteractivegames.Althoughnotproven,there seemstobeacorrelationbetweentheuseofvideogames andobesity,butsomeauthorsstatethattheenergy expendi-tureofplayingvideogamesissimilartothatofwalkingand running.29 _Regularly_playing _active_video _games _may_even havepositiveeffectsonoveralllevelsofchildren’sphysical activity.30

Goingtoschoolcanbephysicalactivity,sincesome chil-drenwalkorcycle,butinchildreninthepresentstudy,the carwasthemostcommontypeoftransportation.Younger childrenwalktoschoollessfrequentlythanolderchildren. Atyoungerages,parentsusuallytakechildrentoandfrom school,mostlybycar.Thecommonuseofmechanicalmeans oftransportationtogotoschoolisassociatedwithalower levelofenergyexpenditure,contributingtoincreased over-weightandobesityinchildren.However,theresultsofthis studydidnotshowasigniﬁcanteffectofthetypeof trans-portonoverweightorobesity.

The fact that TVPC and type of transportation used wereevaluatedthroughaquestionnaireandnotby direct observation is a limitation of this study that may inﬂu-encetheresultsoftheassociationbetweenthesevariables and overweight/obesity. Children sometimes have difﬁ-cultyanswering questionnairescorrectly,astheir recallis limited.31 _However, _this _study _would _have _been _virtually impossibletocarryoutbydirectobservation.

Inconclusion,theprevalenceofoverweightandobesity inchildrenfrom6to13yearsofageintheNortheastregion ofPortugal(Braganc¸aandMacedodeCavaleiros)was32%. Themajorityofchildrengotoschoolbycar,andonly12.2% spendlessthan1.5hourswatchingtelevisionand/orplaying videogames.Boyswhospendlessthan1.5hourswatching televisionand/orplayingvideogamesare75.4%lesslikely tobe overweight/obesethan thosewhospend more than 1.5hours.

Ethic

disclosures

Protection of human and animal subjects.The authors declarethatnoexperimentswereperformedonhumansor animalsforthisinvestigation

Conﬁdentialityofdata.Theauthorsdeclarethattheyhave followedtheprotocolsoftheirworkcenteronthe publica-tionofpatientdataandthatallthepatientsincludedinthe

studyhave receivedsufﬁcientinformationand havegiven theirinformedconsentinwritingtoparticipateinthestudy.

Right to privacy and informed consent.The authors declarethatnopatientdataappearsinthisarticle.

Conﬂicts

of

interest

Theauthorshavenoconﬂictsofinteresttodeclare.

References

1. LobsteinTBL,Uauy R.Obesityinchildrenandyoungpeople: acrisisinpublichealth.ObesRev.2004;5:4---104.

2.WHO.Obesity.Preventingand managingtheglobalepidemic: reportofaWHOconsultationonobesity.Geneva:WHO;1997. 3.ReillyJJ,MethvenE,McDowellZC,etal.Healthconsequences

ofobesity.ArchDisChild.2003;88:748---52.

4.ZametkinAJ,ZoonCK,KleinHW,etal.Psychiatricaspectsof childand adolescentobesity:a reviewofthepast10years. JAmAcadChildAdolescPsychiatry.2004;43:134---50.

5.Baba RKM,Nagashima M,Inasaka H. Roleof exercise inthe preventionofobesityandhemodynamicabnormalitiesin ado-lescents.PediatrInt.2009;51:359---63.

6.Wu DMHY, Sun CA, Sung PK, et al. Familialresemblance of adiposity-relatedparameters:resultsfroma healthcheck-up populationinTaiwan.EurJEpidemiol.2003;18:221---6. 7. Rito A. Overweight and obesity inthe preschool childrenof

Coimbra.ObesRev.2006;7:366.

8.PapandreouC,MouradTA,JildehC,etal.Obesityin Mediter-ranean region (1997---2007): a systematic review. Obes Rev. 2008;9:389---99.

9.PereiraSA,SeabraAT,SilvaRG,etal.Prevalenceofoverweight, obesity and physical activity levels in children from Azores Islands.AnnHumBiol.2010;37:682---91.

10.ColeTJ,BellizziMC,FlegalKM,etal.Establishingastandard deﬁnitionforchildoverweightandobesityworldwide: interna-tionalsurvey.BMJ.2000;320:1240---3.

11.CarvalhalMM,PadezMC,MoreiraPA,etal.Overweightand obe-sityrelatedtoactivitiesinPortuguesechildren,7---9years.Eur JPublicHealth.2007;17:42---6.

12.PadezCMI,MoreiraP,RosadoV.Prevalenceandriskfactorsfor overweightandobesityinPortuguesechildren.ActaPaediatr. 2005;94:1550---7.

13.ManiosY,AngelopoulosPD,KourlabaG,etal.Prevalenceof obe-sityandbodymassindexcorrelatesinarepresentativesample ofCretanschoolchildren.IntJPediatrObes.Jun7.

14. MoreiraP.OverweightandobesityinPortuguesechildrenand adolescents.JPublicHealth.2007;15:155---61.

15.MaGS,LiYP,HuXQ,etal.Effectoftelevisionviewingon pedi-atricobesity.BiomedEnvironSci.2002;15:291---7.

16.HernandezB,GortmakerSL,ColditzGA,etal.Associationof obesity withphysical activity, televisionprograms and other formsofvideoviewingamongchildreninMexicoCity.IntJObes RelatMetabDisord.1999;23:845---54.

17.Arluk SL, Branch JD, Swain DP, et al. Childhood obesity’s relationship to time spent in sedentary behavior. Mil Med. 2003;168:583---6.

18.Bukara-Radujkovic G, Zdravkovic D. Physical activity as an important determinant in developing childhoodobesity. Med Pregl.2009;62:107---13.

19.Mota J, Gomes H, Almeida M, et al. Leisure time physical activity, screen time, social background, and environmental variablesinadolescents.PediatrExercSci.2007;19:279---90. 20. PateRR,TrostSG,FeltonGM,etal.Correlatesofphysical

(6)

21.Goldﬁeld GS. Predictors of response to an intervention modifying physical activity and sedentary behavior in over-weight/obese children: attitudes vs. behavior. J Phys Act Health.2009;6:463---6.

22.ChaputJP,TremblayA.Obesityandphysicalinactivity:the rele-vanceofreconsideringthenotionofsedentariness.ObesFacts. 2009;2:249---54.

23.MagareyAM,DanielsLA,BoultonTJ,etal.Predictingobesityin earlyadulthoodfromchildhoodandparentalobesity.IntJObes RelatMetabDisord.2003;27:505---13.

24. Berndt TJ.Friendship and friends’ inﬂuence inadolescence. CurrDirPsycholSci.1992;1:156---9.

25. GrundA,KrauseH,SiewersM,etal.IsTVviewinganindexof physicalactivityandﬁtnessinoverweightandnormalweight children?PublicHealthNutr.2001;4:1245---51.

26.DuRant RH, Baranowski T, Johnson M, et al. The rela-tionship among television watching, physical activity, and body composition of young children. Pediatrics. 1994;94: 449---55.

27.Andersen RE, Crespo CJ, Bartlett SJ, et al. Relationship of physical activity and television watching with body weight and level offatness among children: results from the Third National Health and Nutrition Examination Survey. JAMA. 1998;279:938---42.

28.Crespo CJ, Smit E, Troiano RP, et al. Television watching, energyintake,andobesityinUSchildren:resultsfromthethird NationalHealthandNutritionExaminationSurvey,1988---1994. ArchPediatrAdolescMed.2001;155:360---5.

29. MaddisonR,MhurchuCN,JullA,etal.Energyexpended play-ingvideoconsolegames:anopportunitytoincreasechildren’s physicalactivity?PediatrExercSci.2007;19:334---43.

30.NiMhurchuC,MaddisonR,JiangY, etal.Couchpotatoesto jumpingbeans:apilotstudyoftheeffectofactivevideogames on physical activity in children. Int JBehav Nutr Phys Act. 2008;5:8.

31.WallaceJP,MckenzieTL.Observedvs.recalledexercise behav-ior:avalidationofasevendayexerciserecallforboys11to13 yearsold.ResQExercSport.1985;52:161---5.