Effects of 12-week overground walking training at ventilatory threshold velocity in type 2 diabetic women

Effects

of

12-week

overground

walking

training

at

ventilatory

threshold

velocity

in

type

2

diabetic

women

Taisa

Belli

*,

Luiz

Fernando

Paulino

Ribeiro

,

Marco

Aure´lio

Ackermann

,

Vilmar

Baldissera

,

Claudio

Alexandre

Gobatto

,

Rozinaldo

Galdino

da

Silva

b_{BiosciencesInstitute,UNESP,RioClaro,SP,Brazil} c_{DepartmentofHealthSciences,UESC,Ilhe´us,BA,Brazil} d_{LaboratoryofExercisePhysiology,UFSCar,Sa˜oCarlos,SP,Brazil} e_{RoraimaStateUniversity,UERR,BoaVista,RR,Brazil}

1.

Introduction

Glycaemic control is a fundamental component in the management of type 2 diabetes mellitus (DM2) and its complications[1,2],withconvincingevidenceshowing physi-caltrainingtobeaneffectivestrategyforthispurpose[3–5]

sinceitincreasesbothglucosetransportandskeletalmuscle insulinsensitivity[6].

Inthis framework, walking hasbeen considered asafe, accessibleandconvenientexercisetypeforindividualswith DM2 without peripheral neuropathy. Given the familiar

pattern ofmovement,walkingexerciseiseasilyaddedinto thedailyphysicalactivityroutineofapatientwithDM2[7,8]. Furthermore, this type of exercise involves large skeletal musclemass,whichplaysamajorroleinperipheralglucose uptake [9], thus triggering more effective improvement in glycaemichomeostasis[10].

Inadditiontothetypeofexercise,otherkeycomponents (i.e.,volume,frequencyandintensity)mustbeconsideredin training programsthat intend tomaximize health benefits whileminimizingrisksinDM2subjects,withspecialattention being devoted tothe exercise intensity [11–15]. In a meta-analysisbyBoule´ etal.[16],reductionsinglycatedhemoglobin

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received3December2010 Receivedinrevisedform 20March2011

Accepted5May2011 Publishedonline1June2011

Keywords:

HbA1c Exercise Type2diabetes Fitness

Ventilatorythreshold

a

b

s

t

r

a

c

t

Thisstudyanalyzedtheeffectsofovergroundwalkingtrainingatventilatorythreshold(VT) velocityonglycaemiccontrol,bodycomposition,physicalfitnessandlipidprofileinDM2 women.Nineteensedentarypatientswererandomlyassignedtoacontrolgroup(CG;n=10, 55.92.2years)oratrainedgroup(TG;n=9,53.42.3years).Bothgroupsweresubjectedto anthropometricmeasures,a12-hfastingbloodsamplingandagradedtreadmillexercise testatbaselineandaftera12-weekperiod,duringwhichTGfollowedatrainingprogram involving overground walking at VT velocity for 20–60min/session three times/week. Significantgrouptimeinteractions(P<0.05)inglycatedhemoglobin(HbA1c),bodymass,

bodymassindex(BMI),peakoxygenuptake(VO2peak)andexercisedurationwereobserved

aseffectsoftrainingexercise,whereasinterventiondidnotinducedsignificantchanges (P>0.05)infastingbloodglucose, submaximalfitnessparametersandlipidprofile.Our

resultssuggestthatovergroundwalkingtrainingatVTvelocityimproveslongterm gly-caemiccontrol,bodycompositionandexercisecapacity,attestingfortherelevanceofthis parameterasaneffectivestrategyfortheexerciseintensityprescriptioninDM2population.

#2011ElsevierIrelandLtd.Allrightsreserved.

*Correspondingauthorat:RuaOscarFerreiradeCarvalho,41,CEP13690-000,VilaVendramini,Descalvado,Sa˜oPaulo,Brazil. E-mailaddress:taisa.belli@gmail.com(T.Belli).

Contentslists availableat ScienceDirect

Diabetes

Research

and

Clinical

Practice

j o u r n alh o m e p a g e :w w w . e l s e vi e r . c o m / l o c at e / d i a b r e s

0168-8227/$–seefrontmatter#2011ElsevierIrelandLtd.Allrightsreserved.

(HbA1c)aftertraininginthesepatientswerebetterpredicted by exercise intensity than volume. Yet, although current positionstatementsfrom differentworld leading organiza-tions[17–19]provideexerciseintensityrecommendationsfor such population, thesesuggestions should beviewed with caution given the wide range of moderate and vigorous intensities based on percentages of maximal oxygen con-sumption(VO2max)(40–59and60–84%)and/ormaximalheart

rate (HRmax) (50–69 and 70–89%). It is well known that

exercisingatagivenpercentageofVO2maxorHRmaxcanelicit

differentphysiologicalresponsesfordifferentindividualsand thatsubmaximalparameterssuchaslactateorgasexchange thresholdsarebettermarkersoftherelativestressinducedby exercise[20].

Regardless of the controversy about its physiological background [21], ventilatorythreshold (VT), or the exercise intensityabove whichventilationbeginstoincrease dispro-portionatelyrelativetooxygenuptake,hasbeenconsidereda direct, simple and useful parameter for optimal exercise intensityprescription in DM2patients[22–24]. While acute exerciseatVTreducesplasmaglucose[25],trainingatthis intensityimproves boththe aerobiccapacityand the cost-effectiveness of treatment [26]. Moreover, Belli et al. [24]

showed the feasibility of VT determination during graded treadmilltestinwomenwithDM2withoutcomplications.In spite ofthis,inmoststudiesadoptingwalking exercisefor DM2patients,intensitywaseithersubjective[7,27,28]orbased

on%HRmax[8,11,29–31].

Although VT accessed in a graded exercise test can be expressed inbothperformance (i.e.,power or velocity) and physiological(i.e.,%VO2maxand%HRmax)terms[24],heartrate

(HR) at VT has been the preferred parameter for exercise prescriptioninclinicalsettings[20,26].However,despitethe increasing availability of portable monitors, continuous HR assessmentduringtrainingsessionsisnotwithoutlimitations

[32]andcanbequitecomplexduetotechnicalandlearning reasons.Alternatively,intensitycontrolbymeansofvelocityin cyclicactivitiessuchasrunningandwalkingisverypracticalin field settings, where subjects are commonly aware about covering known distances in particular times. Yet, the effectivenessoftrainingovergroundatVTvelocitiesderived from treadmill tests in patients with DM2 remains to be investigated.Thus,thepurposesofthisstudyweretoassessthe effectsofsupervisedovergroundwalkingtrainingatventilatory thresholdvelocityonHbA1c,bloodglucose,bodycomposition, physicalfitnessandlipidprofileintype2diabeticwomen.

2.

Materials

and

methods

2.1. Subjects

Afterapproval by the Sa˜o Carlos Federal University Ethics Committee for Human Research (no 034/04), 24 sedentary middle-agedwomenwithDM2diagnosis[33]wererecruited fromlocalhealthfacilitiesandsignedaninformedconsent volunteeringtotakepartinthisinvestigation.Allofthemwere housewives,non-smokersandnotengagedinregularexercise practice, withcurrent physicalactivity <1h/week. Patients

wereincludedinthestudyiftheirdiabeteswastreatedbydiet

(n=5)ororalagents(sulphonylurea,n=6;metformin,n=3; andsulphonylurea+metformin,n=10),butnotiftheywere treated with insulin given the tendency of an advanced diseasestateinthiscase.Absenceoflongtermcomplications (retinopathy,microalbuminuria,nephropathy,peripheraland autonomicneuropathy)aswellasbloodpressuregreaterthan 160/95mmHg were confirmed by clinical history, clinical examinationandlaboratorytests.Afterablinded randomiza-tion by means of computer-generated random numbers subjectswereallocatedinacontrol(CG)oratrainedgroup (TG), each one with 12 volunteers. Five of the 24 women initiallyenrolledinthestudywerenotabletoconcludethe experimentalprotocol(2fromCGand3fromTG)duetofamily responsibilities (n=3), thrombosis (n=1) and spinal disc herniation (n=1),being theselast events notattributed to the study procedures. Therefore, our final sample was composedby10and9subjectsintheCGandTG,respectively. Nosignificantdifferenceswerefoundbetweengroupsforage (55.92.2vs53.42.3years,P=0.48),height(155.01.6vs 152.02.4cm,P=0.30)anddiseasetime(3.70.8vs4.41.2 years,P=0.71).

2.2. Experimentalprocedures

Usingalongitudinalapproach,allpatientsweresubmittedto anthropometric measurements, a 12-h fasting blood sam-pling, dietary evaluation and a graded exercise test on a motorizedtreadmillatbaselineandaftera12-weekperiod. Exercisetest(TGonly)anddietaryevaluation(TGandCG)were also performedat the 6th week.Subjects fromthe trained groupwereevaluated48–72hafterthelasttrainingsessionin ordertoavoidresidualinfluenceofacuteexercise.

2.3. Anthropometry

Height was accessed using a calibrated stadiometer (Filiz-zola1_{, Brazil), while body mass and body composition}

including percent body fat, fat and fat free mass, were determined usinga bioelectricimpedancesystem withthe electrodesincontactwithsolesandheelsofbothfeet(Tanita Body Composition Analyzer TBF-310) [34]. Measurements wereperformedinaquietenvironmentaftera12-hovernight fast,beingthesubjectsinthestandingpositionwithoutshoes andusinglightclothes.Bodymassindex(BMI)wascalculated as body mass divided by squared height (kg/m2_{). Waist}

circumferences were taken at narrowest circumference betweenthelowestribandtheiliaccrestbyasingletrained evaluatorusinganinextensiblemetallictape(Sanny1_,Brazil)

placeddirectlyontheskin,perpendicularlytothelongaxisof thebody andhorizontallytothefloorattheendofnormal expiration.Forthispurpose,subjectsstoodwithfeettogether, lookingstraightaheadwiththearmshangingbythesideof thebody[35].Averagevaluesfromtwomeasurementswere considered.

2.4. Bloodanalysis

analysisofbloodglucoseandlipidprofile.Bloodglucose,total cholesterol,highdensitylipoproteincholesterol(HDLC)and triglycerides were determined by enzymatic-colorimetric procedures (Laborlab1_{)using aspectrophotometer}

(VERSA-Max1_{microplatereader).Lowdensitylipoproteincholesterol}

(LDLC) was determined using Friedwald’s equation for triglycerides<400mg/dL. Additional 2mL blood samples

weretakenintubescontainingEDTAforHbA1cdetermination usinghigh-performanceliquidchromatography(BioRad Dia-STATAnalyzer1_).

2.5. Dietaryevaluation

Fordietaryevaluation,a1-dayfoodrecordwasadoptedina facetofaceinterviewconductedbyanexperienceddietitian. Thereafter, records were analyzed using the ‘‘Nutrition Support Program’’ software from the Escola Paulista de Medicina–EPM (DIS-EPM, version 2.5a, UNIFESP, Brazil). It was recommended a dietary education according to the American Diabetes Association (ADA) position statement

[36] to all subjects to minimize dietary variability among groups.

2.6. Gradedexercisetests

After a familiarization session, graded exercise tests were conducted using a previously described protocol [24] on a treadmill (Moviment – LX-160, Brazil) without inclination. Initialvelocitywas set at 1km/h and increasedby 1km/h every2minuntilvoluntaryexhaustion.Duringexercise,20s average ventilation (VE), oxygen uptake (VO2) and carbon

dioxideproduction(VCO2)weremonitoredwithsubjectsusing

a nose clip and breathing into a mouthpiece (VO2000 Gas Analyzer,MedGraphics,USA).Thesystemwasautomatically calibratedbeforeeachtestandsubjectswereallowedtolightly rest their hands on the treadmill bar during exercise to maintaintheirbalance.ThehighestVO2attainedduringthe

testwastakenasthepeakoxygenuptake(VO2peak).VTwas

assessedby twoindependent investigatorsthroughVE/VO2

increasewithout a concomitant rise inVE/VCO2[37]. After

20minsitting rest precedingthe exercisetest, participants hadassessedtheirbloodpressurebytheauscultatorymethod usingananeroidsphygmomanometer (Tycos,USA1_{)and a}

stethoscope (Becton Dickinson, USA1_{). Furthermore, blood}

pressureandheartrate(PolarS810,PolarElectroOy,Finland1₎

weremeasuredat theendofeachstageforsafetyreasons duringthetest.

2.7. Trainingprotocol

WomenfromTGweresubjectedtoa12-weekwalkingtraining program,whichwasperformedinaflat350moutdoortrackat the individual VT velocity, three times a week (Monday, WednesdayandFriday).Alltrainingsessionsweresupervised and performed between 8:00 and 10:00a.m. Stretching exercisesinvolvingmainmusclegroupsofupperandlower limbswereperformedbeforeandafterwalkingandindividual velocitieswerecontrolledbythefirstauthorduringalltraining sessions.Forthispurpose,sonoroussignalswereprovidedin ordertodrivesubjectstopassbymarksplaced50mapartin

the track in pre-determined times. After a familiarization sessionpriortothefirsttrainingbout,allsubjectswereableto keeptheprescribedvelocityusingthisprocedurewithinfew minutes,whichhasbeenpreviouslyadoptedinfield rehabili-tation [38]. In the first week sessions lasted 20min, being duration increasedby10min/week until60minat the 5th week.Thisdurationwaskeptuntiltheendoftrainingperiod. Agradedexercisetestwascarriedoutattheendofthe6th weekinordertoadjusttrainingspeeds.Furthermore,inthe lasttrainingsessionofeachtwoweeks,preandpostexercise fingertipbloodsamplesweretakeninordertoverifytheacute effectsoftheboutandassurethatbloodglucose(Optimum– MedisenseProduct,AbbottLab1_{)waskeptinthesaferange}

suggestedbyADA[39].VolunteersfromtheCGcontinuedtheir normal lives without any systematic exercise during the experimentalprotocol.

2.8. Statisticalanalysis

Statisticalanalysiswascarriedoutusingastatisticalsoftware package (Statistic 7.0, Statsoft, Tulsa, USA). Mean and standarderrorofmean(SEM)werecalculatedforallstudied variables.Normaldistributionandhomogeneityofthedata were verified by the Shapiro-Wilk and Levene’s tests, respectively, and before using parametric analysis blood glucose, triglycerides, maximal and submaximal velocities werelog transformed.Group comparisonsat baselinewere carried out using unpaired t tests. Two-way 22 (group

time)mixedanalysisofvariances(ANOVAs)wereusedto investigate main effects and grouptime interactions. Dietaryparameterswereanalyzedbymeansof23(group

time)mixedANOVAs,beingGreenhouse-Geissercorrection applied if violationofsphericity was pointedbyMauchly’s test. Unequal n Tukey post hoc test was performed when appropriate.StatisticalsignificancewassetatP<0.05inall

cases.

3.

Results

No significant differences (P>0.05) were found between

trained and control groups for any studied variable at baseline (Tables 1 and 2, Fig. 1), and high attendance to the supervisedtraining programwasobservedforthe TG, withvolunteers performing922%of36offeredsessions. Capillary blood glucose significantly decreased (P<0.01)

after all selected bouts in this group, being averaged pre andpostexercisevaluesrespectively1628vs1187mg/ dL.Nosignificant changes(P>0.05) werefound infasting

blood glucose before and after experimental period (TG: 1199and1108mg/dL;CG:13216and14220mg/dL). On theotherhand,whileCGshowedsimilarHbA1clevels aftertraining,apronounced11.6%decreasewasfoundinTG, leading to a significant (P<0.05) grouptime interaction

(Fig.1).

interactionsstatistically significantforall theseparameters (P<0.01).Whilefatfreemassremainedratherstableinboth

groups,fatmassandpercentagebodyfatdecreasedtoagreat extentinTG,butonlysignificanttimeeffects(P<0.01)were

foundforthesechanges.Regardinglipidprofile,asignificant grouptimeinteractionwasfoundforHDLC(P<0.05),witha

greaterincreaseincontrolvstrainedgroup.Incontrast,both groups showed lower total cholesterol and LDLC after 12-weeks, with a significant time effect (P<0.01) and no

significant changes were found fortriglycerides as wellas restingbloodpressure(P>0.05).

Table 2 shows fitness parameters accessed during the

graded exercise tests at baseline and after intervention. Greater increases in peak treadmill velocity and exercise durationwereobservedintheTG,butasignificantinteraction wasfoundonlyforthelatter(P<0.05).Asignificantgroup

timeinteraction (P<0.05)was alsoobserved forVO_2peak,

witha6%increaseintheTGbutan8%reductionintheCG.In addition,whilenosignificantchangeswerefoundforHRpeak,

slightlyhigherrespiratoryexchangeratio(RER)valuesinboth groupsafter12weeksledtoasignificanttimeeffect(P<0.05).

Regardingsubmaximalparameters,velocityatVTincreasedto agreatextentinTG(17vs7%),butonlysignificanttimeeffect

(P<0.01)werefoundforthischange.Ontheotherhand,no

significantmaineffectsorinteractionswereobservedforVT expressedinphysiologicterms(P>0.05).

Energyintakeat baseline,atthe 6thweekandafterthe experimental period in TG and CG were respectively 7569753 and 7971791kJ/day, 6514506 and 5912594kJ/day, and 6828456 and 5912414kJ/day. A significanttimeeffect(P<0.05)wasfoundforthisvariable,

withpost-hocanalysisshowinglowerenergyintakeat6thand 12-weeks(P<0.05)comparedtobaselinevalues.Ontheother

hand,nosignificantgroupeffectorgrouptimeinteraction

Table1–Anthropometricmeasures,lipidprofileandrestingbloodpressurefortrainedgroup(TG)andcontrolgroup(CG) atbaselineandafter12-weeks.

TG(n=9) CG(n=10) ANOVAP-value

Baseline 12-Weeks Baseline 12-Weeks Group Time Interaction

Bodymass(kg) 75.06.1 72.55.9 71.84.2 71.44.2 0.77 <0.01 <0.01

Bodymassindex(kg.m 2_{) 32.2}

2.0 31.11.9 29.91.8 29.81.8 0.51 <0.01 <0.01

Fat-freemass(kg) 44.41.9 45.42.8 44.51.4 45.21.5 0.99 0.11 0.77

Fatmass(kg) 30.64.2 27.23.4 27.52.8 26.22.8 0.66 <0.01 0.06

Bodyfat(%) 39.52.4 36.61.9 37.31.9 35.72.2 0.61 <0.01 0.27

Waist(cm) 100.83.3 100.73.5 101.14.1 103.14.1 0.81 0.03 0.01

Totalcholesterol(mg/dL) 202.110.7 184.811.3 233.419.5 202.915.1 0.23 <0.01 0.39

HDLC(mg/dL) 34.32.3 42.02.9 33.02.5 52.34.8 0.29 <0.01 0.02

LDLC(mg/dL) 141.911.7 109.912.9 169.918.2 119.310.9 0.39 <0.01 0.16

Triglycerides(mg/dL) 179.342.6 164.323.3 191.654.3 156.719.6 0.91 0.77 0.85

RestingSBP(mmHg) 130.06.9 117.09.4 138.04.5 130.08.4 0.24 0.07 0.68

RestingDBP(mmHg) 83.63.8 77.04.7 84.43.3 81.03.9 0.56 0.17 0.58

HDLC:highdensitylipoproteincholesterol,LDLC:lowdensitylipoproteincholesterol,SBP:systolicblood pressure,DBP:diastolic blood pressure.

Table2–Fitnessparametersfortrainedgroup(TG)andcontrolgroup(CG)atbaselineandafter12-weeks.

TG(n=8) CG(n=9) ANOVAP-value

Baseline 12-Weeks Baseline 12-Weeks Group Time Interaction

Peakvelocity(km.h 1_{) 6.2}

0.3 8.00.4 6.70.2 6.90.3 0.01 <0.01 0.27

Exerciseduration(min) 13.30.7 15.70.7 12.90.4 13.70.6 0.15 <0.01 0.04

VO2peak(ml.kg 1_min 1_{) 22.1}

1.23 23.31.4 23.91.4 21.71.2 0.87 0.28 0.03

HRpeak(bpm) 1494 1575 1609 1575 0.60 0.56 0.26

RERpeak 1.140.13 1.190.06 1.090.05 1.180.06 0.37 0.01 0.38

VelocityatVT(km.h 1_{) 4.70.3 5.40.2 4.70.2 5.00.2 0.99 <0.01 0.98}

VO2atVT(ml.kg 1_min 1_{) 16.40.9 16.41.1 18.70.8 15.60.8 0.51 0.06 0.06}

%VO2peakatVT 721 723 753 712 0.59 0.49 0.52

HRatVT(bpm) 1184 1187 1176 1236 0.74 0.65 0.19

%HRpeakatVT 803 753 744 783 0.53 0.81 0.21

VO2:oxygenuptake,HR:heartrate,RER:respiratoryexchangeratio,VT:ventilatorythreshold.

(P>0.05)wereobserved.Nosignificantdifferencesorchanges

werefoundformacronutrientcompositionofthediet(data notshown).

4.

Discussion

Themainfindingsofthepresentstudywerethat12-weeksof supervisedwalkingtrainingat VTvelocityledtosignificant improvementsinlongtermglycaemiccontrol,body composi-tionandexercisecapacityinmiddle-agedDM2women.Onthe otherhand,suchinterventionhadnosignificanteffectson fastingbloodglucoseorlipidprofileinthesepatients.

Inlinewithexistingevidence[24],whenexpressedrelative toVO2peakandHRpeakhighinter-individualvariabilityofVT

wasobservedinourvolunteers(60to85%),butdespitethis intensityhasbeenclaimedasamarkerforoptimalexercise prescriptioninDM2subjects[22–24]toourknowledgethisis the first study addressing the chronic effects of a full supervisedwalkingprogramatVTvelocityinthesepatients. Interestingly,thereductioninHb1AcobservedinourTG (11.6%)wasgreaterthanthosefoundintheonlytwoprevious studiesshowingimprovementsinlongtermglycaemiccontrol afterwalkingtraininginpatientswithDM2[7,31].Walkeretal.

[7]showed12-weekofselfpacedwalkingfor60min,fivetimes a week, to lower HbA1c by 7.6% in postmenopausal DM2 women,whileShenoyetal.[31]founda9.7%decreaseinthis parameterafteran8-weekexerciseprogramat 75to83% HRmaxfor35to40min,fivetimesaweek,inAsianIndiansof

bothgenderswithDM2.

Contrarytothesestudieshowever,reducedHbA1cinthe presentinvestigationwasnotaccompaniedbylowerfasting bloodglucose.Giventhathemoglobinglycationdependson meanbloodglucoseconcentrationoverthe120-daylifespan ofredblood cells[40],thisapparently contradictoryfinding couldresultfromtheacuteeffectsofeachexercisebout in loweringbloodglucose.Inlinewiththis,Mandersetal.[41]

foundasingleboutofexercisetoreduceaveragebloodglucose concentrationandtheprevalenceofhyperglycemiaduringthe 24-hpostexerciseperiod.Meancapillaryglycaemiareduction observedinoursubjectsinselectedtrainingboutswas27%, beingthesevaluesintheadequaterange(70–300mg/dL)for exercise practice suggested by ADA [39], attesting for the safetyourwalkingprogram.

Corroboratingpreviousstudies,ourresultsshowed walk-ingtraining toreducebody massandBMIinDM2patients

[7,27–29,31]. In addition, we found a tendency to greater

reductioninfatmasswithoutchangesinfat-freemassasa resultofexercise, that alsoprevented waistcircumference increase,whichinturnisstronglyrelatedtovisceraladipose tissue,insulinresistanceandcardiovascularcomplicationsin

DM2 [42–44]. Together, these findings indicate a healthier

anthropometric profile and consequent protection against obesityrelatedco-morbiditiesinoursubjectsaftertraining.

Enhancementonlipidprofileincludingreductionsontotal cholesterolandLDLChasbeenobservedinsomebutnotall walkingtrainingstudies[7,8,26,27].Abnormallipidprofilewas observedinoursubjectsatbaseline,however,unexpectedly changestowardstargetvalueswerefoundafterexperimental period in both groups. These results may be partially

explained by diet characteristics that were not accounted forinourstudyprotocol,suchasreductionsinsaturatedfat,

transfatandcholesterolintakeoralsoincreasedviscousfiber andn-3fattyacidsingestion[45].Inaddition,despitethelack ofsignificantgrouporgrouptimeinteraction,totalenergy intakedecreasedtoagreatextentincontrolvstrainedgroup throughtheexperimentalperiod(25vs10%).Thiscanalso elucidatethegreaterHDLCincreaseincontrolvstrainedgroup afterintervention.

ThesignificantgrouptimeinteractionsforVO2peakand

exercisedurationcorroboratedatafrompreviousstudies[7,30]

and canbeconsidered evidencesthat ourwalking training protocol wasabletoimproveexercisecapacity/tolerancein DM2 subjects. These are relevant adaptations since low cardiorespiratory fitness is a common feature related to femalegender,familyhistoryofcoronaryheartdisease[46]

andanindependentpredictorofmortality[47]inpeoplewith DM2.Contrarytothehypothesisthattrainingwouldelicita greater increase in VTcomparedto VO2peak, wefound the

former to be unchanged after the intervention when expressedinphysiologicalterms.Insupportofthis,Larose et al. [48] observed that workload at VT increased while %VO2peak at VT remained unchanged after 6-months of

walking and cycling at 60–75% HRmax for 25–45min, three

timesaweekinpatientswithDM2.

Yet regular walking has been considered an interesting adjuncttherapyforDM2subjects,controversialfindingshave been reported regarding thechronic effects ofthis type of exercise on health related parameters in such population

[7,8,11,26–31].Thesedivergencesmayresultfromthediversity

ofadoptedtrainingperiods(fewweeksuptoayear),exercise frequencies (2–5 days/week), session durations (30–60min) andintensities(subjectiveselfpaced,briskwalking,%HRmax),

aswellassamplecharacteristics(age,gender,race).

SinceoursubjectsexercisedatVTvelocitiesderivedfrom treadmill tests one could question whether training was performedat VTintensityexpressedinphysiologicalterms (i.e.,%HRpeakor%VO2peak)duetoenvironmentaland

specifici-ty concerns. Inanattempttominimizetheclimatic differ-ences between laboratory and field conditions, testing and trainingsessionswereperformedatapproximatelythesame timeoftheday.Inaddition,trainingprogramwasdeliberately conducted during the spring, with rather stable climatic conditionsinoursubtropicalregion.Albeitthesecautionsdo notwarrantidenticalenvironments,differenceswere proba-bly too small to result in rather discrepant physiological strains. Ontheotherhand,fromtheresultsofParvataneni et al. [49]indicating lower metabolic requirement in over-groundcomparedtotreadmillwalkingatthesamevelocityin older adults,it isplausiblethatourvolunteers’ VTvelocity couldbegreaterifdeterminedonthetrack.Alimitationofthe currentinvestigationhoweverwasthatwecouldnotquantify the extent to which overground walking differed from treadmillwalkinginphysiologicalterms.

littlecomorbidityandshortdiseaseduration,reachingsuch low Hb1Ac values without hypoglycaemia episodes may provide important reductions in the risk of microvascular complications[45].Whiletheseresultspointoutthe effective-nessofafieldwalking programatthe laboratorybasedVT velocityinDM2subjects,indicessuchasthemaximallevelof lipid oxidation, which is lower than VT, have been also suggestedforoptimizingexerciseintensityinpatientswith metabolic diseases [50]. Nevertheless, the issue of which individualized target is more efficient or even whether individualization is superior than standard procedures for patientswithDM2isarelativelynewresearchareaandfurther workonthistopiciswarranted.

Acknowledgements

ThisstudywassupportedbytheCAPES,Brazil.WethankDM2 patients; Medical Laboratory Dr Maricondi – Ma´rcio Lopes Bandoni;ExercisePhysiologyResearchGroup/UFSCar; Depart-mentof Morphologyand Pathology/UFSCar; Departmentof PhysiologicalSciences/UFSCar;DescalvadoTownHall–Carlos Roberto Bianchi; ViaSau´deGym – Regilene;Paula Scramin O‘hara;SimonePizzaFregonesiandMarianaRinaldiBenvenga fortheircontributiontothisstudy.

Conflict

of

interest

Theauthorsdeclarethattheyhavenoconflictofinterest.

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[1] UKProspectiveDiabetesStudy(UKPDS)Group.Intensive bloodglucosecontrolwithsulphonylureasorinsulin comparedwithconventionaltreatmentandriskof complicationsinpatientswithtype2diabetes(UKPDS33). Lancet1998;352:837–53.

[2] UKProspectiveDiabetesStudy(UKPDS)Group.Effectof intensiveblood–glucosecontrolwithmetforminon complicationsinoverweightpatientswithtype2diabetes (UKPDS34).Lancet1998;352:854–61.

[3] Boule´ NG,HaddadE,KennyGP,WellsGA,SigalRJ.Effectof exerciseonglycemiccontrolandbodymassintype2 diabetesmellitus.Ameta-analysisofcontrolledclinical trials.JAMA2001;2861:218–1227.

[4] CastanedaC,LayneJE,Munoz-OriansL,GordonPL, WalsmithJ,FoldvariM,etal.Arandomizedcontrolledtrial ofresistanceexercisetrainingtoimproveglycemiccontrol inolderadultswithtype2diabetes.DiabetesCare 2002;25:2335–41.

[5] SigalRJ,KennyGP,Boule´ NG,WellsGA,Prud’hommeD, FortierM,etal.Effectsofaerobictraining,resistance training,orbothonglycemiccontrolintype2diabetes:a randomizedtrial.AnnInternMed2007;147:357–69. [6] JessenN,GoodyearLJ.Contractionsignalingtoglucose

transportinskeletalmuscle.JApplPhysiol2005;99:330–7. [7] WalkerKZ,PiersLS,PuttRS,JonesJA,O‘DeaK.Effectsof regularwalkingoncardiovascularriskfactorsandbody compositioninnormoglycemicwomenandwomenwith type2diabetes.DiabetesCare1999;22(4):555–61.

[8] PraetSFE,vanRooijESJ,WijtvlietA,Boonman-deWinter LJM,EnnekingTh,KuipersH,etal.Briskwalkingcompared withanindividualmedicalfitnessprogrammeforpatients withtype2diabetes:arandomisedcontrolledtrial. Diabetologia2008;51:736–46.

[9] IvyJL.Muscleinsulinresistanceamendedwithexercise training:roleofGLUT4expression.MedSciSportsExerc 2004;36:1207–11.

[10] BorghoutsLB,KeizerHA.Exerciseandinsulinsensitivity. IntJSportsMed2000;21:1–12.

[11] JohnsonST,McCarranLJ,BellGJ,Tudor-LockeC,HarberVJ, BellRC.Walkingfaster:distillingacomplexprescriptionfor type2diabetesmanagementthroughpedometry.Diabetes Care2006;29:1654–5.

[12] SnowlingNJ,HopkinsWG.Effectsofdifferentmodesof exercisetrainingonglucosecontrolandriskfactorsfor complicationsintype2diabeticpatients:ameta-analysis. DiabetesCare2006;29:2518–27.

[13] HansenD,DendaleP,JonkersRAM,BeelenM,MandersRJF, CorluyL,etal.Continuouslow-tomoderate-intensity exercisetrainingisaseffectiveasmoderate-to high-intensityexercisetrainingatloweringbloodHbA1c inobesetype2diabetespatients.Diabetologia 2009;52:1789–97.

[14] HawleyJA,GibalaMJ.Exerciseintensityandinsulin sensitivity:howlowcanyougo?Diabetologia2009;52: 1709–13.

[15] ZanusoS,JimenezA,PuglieseG,CoriglianoG,BalducciS. Exerciseforthemanagementoftype2diabetes:areviewof theevidence.ActaDiabetol2010;47:15–22.

[16] Boule´ NG,KennyGP,HaddaE,WellsGA,SigalRJ. Meta-analysisoftheeffectofstructuredexercisetrainingon cardiorespiratoryfitnessintype2diabetesmellitus. Diabetologia2003;46:1071–81.

[17] AlbrightA,FranzM,HornsbyG,KriskaA,MarreroD,Ullrich I,etal.AmericanCollegeofSportsMedicinePositionStand: exerciseandtype2diabetes.MedSciSportsExerc 2000;32:1345–60.

[18] SigalRJ,KennyGP,WassermanDH,Castaneda-SceppaC, WhiteRD.Physicalactivity/exerciseandtype2diabetes. DiabetesCare2006;29:1433–8.

[19] MarwickT,HordernM,MillerT,ChyunD,BertoniA, BlumenthalR,etal.Exercisetrainingfortype2diabetes mellitusimpactoncardiovascularrisk:ascientific statementfromtheAmericanHeartAssociation. Circulation2009;119:3244–62.

[20] MeyerT,LuciaA,EarnestCP,KindermannW.Aconceptual frameworkforperformancediagnosisandtraining prescriptionfromsubmaximalgasexchangeparameters– theoryandapplication.IntJSportsMed2005;26:S38–48. [21] HopkerJG,JobsonSA,PanditJJ.Controversiesinthe

physiologicalbasisofthe‘anaerobicthreshold’andtheir implicationsforclinicalcardiopulmonaryexercisetesting. Anaesthesia2011;66:111–23.

[22] FujitaY,KawajiK,KanamoriA,MatobaK,YajimaY, TakeuchiA,etal.Relationshipbetweenage-adjustedheart rateandanaerobicthresholdinestimatingexercise intensityindiabetics.DiabetesResClinPract1990;8:69–74. [23] KunitomiM,TakahashiK,WadaJ,SuzukiH,MiyatakeN,

OgawaS,etal.Re-evaluationofexerciseprescriptionfor Japanesetype2diabeticpatientsbyventilatorythreshold. DiabetesResClinPract2000;50:109–15.

[24] BelliT,AckermannMA,RibeiroLF,LangeaniR,Galdinoda SilvaR,BaldisseraV.Lactateandventilatorythresholds intype2diabeticwomen.DiabetesResClinPract 2007;76:18–23.

ofexercisefordiabetics.DiabetesResClinPract1989;6: 303–9.

[26] BrunJ-F,BordenaveS,MercierJ,JaussentA,PicotM-C, PrefautC.Cost-sparingeffectoftwice-weeklytargeted endurancetrainingintype2diabetics:Aone-year controlledrandomizedtrial.DiabetesMetab2008;34: 258–65.

[27] FritzT,Wa¨ndellP,AbergH,EngfeldtP.Walkingfor exercise—doesthreetimesperweekinfluenceriskfactors intype2diabetes?DiabetesResClinPract2006;71:21–7. [28] TrenellMI,HollingsworthKG,LimEL,TaylorR.Increased

dailywalkingimproveslipidoxidationwithoutchangesin mitochondrialfunctionintype2diabetes.DiabetesCare 2008;31:1644–9.

[29] JohnsonST,BellGJ,McCargarLJ,WelshRS,BellRC. Improvedcardiovascularhealthfollowingaprogressive walkinganddietaryinterventionfortype2diabetes. DiabetesObesMetab2009;11:836–43.

[30] MortonRD,WestDJ,StephensJW,BainSC,BrackenRM. Heartrateprescribedwalkingtrainingimproves cardiorespiratoryfitnessbutnotglycaemiccontrolin peoplewithtype2diabetes.JSportsSci2010;28:93–9. [31] ShenoyS,GuglaniR,SandhuJS.Effectivenessofanaerobic

walkingprogramusingheartratemonitorandpedometer ontheparametersofdiabetescontrolinAsianIndianswith type2diabetes.PrimaryCareDiabetes2010;4:41–5. [32] AchtenJ,JeukendrupAE.Heartratemonitoring:

applicationsandlimitations.SportsMed2003;33:517–38. [33] ExpertCommitteeontheDiagnosisandClassificationof DiabetesMellitus.Reportoftheexpertcommitteeonthe diagnosisandclassificationofdiabetesmellitus.Diabetes Care2000;23:S4–19.

[34] TsuiEY,GaoXJ,ZinmanB.Bioelectricalimpedance analysis(BIA)usingbipolarfootelectrodesinthe assessmentofbodycompositionintype2diabetes mellitus.DiabetesMed1998;15:125–8.

[35] KleinS,AllisonDB,HeymsfieldSB,KelleyDE,LeibelRL, NonasC,etal.Waistcircumferenceandcardiometabolic risk:aconsensusstatementfromShapingAmerica’s Health:AssociationforWeightManagementandObesity Prevention;NAASO,theObesitySociety;theAmerican SocietyforNutrition;andtheAmericanDiabetes Association.DiabetesCare2007;30:1647–52.

[36] BantleJP,Wylie-RosettJ,AlbrightAL,ApovianCM,Clark NG,FranzMJ,etal.Nutritionrecommendationsand interventionsfordiabetes.Apositionstatementof theAmericanDiabetesAssociation.DiabetesCare 2008;31:S61–78.

[37] CaiozzoVJ,DavisJA,EllisJF,AzusJL,VandagriffR,Prietto CA,etal.Acomparisonofgasexchangeindicesusedto

detecttheanaerobicthreshold.JApplPhysiol1982;53: 1184–9.

[38] Herna´ndezMTE,RubioTM,RuizFO,RieraHS,GilRS, Go´mezJC.Resultsofahome-basedtrainingprogramfor patientswithCOPD.Chest2000;118:106–14.

[39] ZinmanB,RudermanN,CampaigneBN,DevlinJT, SchneiderSH.Physicalactivity/exerciseanddiabetes mellitus.DiabetesCare2003;26:S73–7.

[40] KilpatrickES.HaemoglobinA1cinthediagnosis andmonitoringofdiabetesmellitus.JClinPathol 2008;61:977–82.

[41] MandersRJF,VanDijkJ-WM,VanLoonLJC.Low-intensity exercisereducestheprevalenceofhyperglycemiaintype2 diabetes.MedSciSportsExerc2010;42:219–25.

[42] PouliotMC,Despre´sJP,LemieuxS,MoorjaniS,BouchardC, TremblayA,etal.Waistcircumferenceandabdominal sagittaldiameter:bestsimpleanthropometricindexesof abdominalvisceraladiposetissueaccumulationand relatedcardiovascularriskinmenandwomen.AmJ Cardiol1994;73:460–8.

[43] SoneH,TanakaS,IimuroS,OidaK,YamasakiY,Ishibashi S,etal.Waistcircumferenceasacardiovascularand metabolicriskinJapanesepatientswithtype2diabetes. Obesity2008;17:585–92.

[44] BlahaMJ,GebretsadikT,ShintaniA,ElasyTA.Waist circumference,notthemetabolicsyndrome,predicts glucosedeteriorationintype2diabetes.Obesity 2008;16:869–74.

[45] AmericanDiabetesAssociation(ADA).Standards ofmedicalcareindiabetes–2010.DiabetesCare 2010;33:S11–61.

[46] Ugur-AltunaB,AltunbA,TatlibE,TugrulA.Factorsrelated toexercisecapacityinasymptomaticmiddle-agedtype2 diabeticpatients.DiabetesResClinPract2005;67:130–6. [47] WeiM,GibbonsLW,KampertJB,NichamanMZE,BlairSN.

Lowcardiorespiratoryfitnessandphysicalinactivityas predictorsofmortalityinmenwithtype2diabetes.Ann InternMed2000;132:605–11.

[48] LaroseJ,SigalRJ,Boule´ NG,WellsGA,Prud’hommeD, FortierMS,etal.Effectofexercisetrainingonphysical fitnessintype2diabetesmellitus.MedSciSportsExerc 2010;42:1439–47.

[49] ParvataneniK,PloegL,OlneySJ,BrouwerB.Kinematic, kineticandmetabolicparametersoftreadmillversus overgroundwalkinginhealthyolderadults.ClinBiomech 2009;24:95–100.